MedWorm.com provides a medical RSS filtering service. Over 6000 RSS medical sources are combined and output via different filters. This feed contains the latest items from the 'BJ Plant' source. Mon, 06 Feb 2012 13:31:36 +0100 http://www.medworm.com/index.php?rid=5603667&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111792 In this study, we performed yeast two-hybrid screening to identify partner MAPKs for OsMKK6, a rice MAPK kinase, and revealed specific interactions of OsMKK6 with OsMPK3 and OsMPK6. OsMPK3 and OsMPK6 each co-immunoprecipitated OsMKK6, and both were directly phosphorylated by OsMKK6 in vitro. A MBP kinase assay of the immunoprecipitation complex indicated that OsMPK3 and OsMPK6 were activated in response to a moderately low temperature (12°C) but a severely low temperature (4°C) in rice seedlings. A constitutively active form of OsMKK6, OsMKK6DD, showed elevated phosphorylation activity against OsMPK3 and OsMPK6 in vitro. OsMPK3, but not OsMPK6, was constitutively activated in transgenic plants overexpressing OsMKK6DD, indicating that OsMPK3 is an in vivo target of OsMKK6. Enh... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5603667 Mon, 16 Jan 2012 05:00:00 +0100 5603667 http://www.medworm.com/index.php?rid=5568545&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111308 Tyrosyl-DNA phosphodiesterase 1 (TDP1), a member of the phospholipase D (PLD) superfamily, catalyzes the hydrolysis of a phosphodiester bond between a tyrosine residue and the 3′-phosphate of DNA. We previously identified and characterized the AtTDP gene in Arabidopsis thaliana, an orthologue of yeast and human TDP1 genes (Lee et al (2010) Plant Physiology 154; 1460-1469). Sequence alignment of TDP1 orthologues revealed that AtTDP has both a conserved C-terminal TDP domain and, uniquely, an N-terminal SMAD/forkhead-associated (FHA) domain. To help understand the function of this novel enzyme, we analyzed the substrate saturation kinetics of full­length AtTDP versus a truncated AtTDP mutant lacking the N–terminal FHA domain. The recombinant AtTDP protein hydrolyzed a singl... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5568545 Tue, 03 Jan 2012 05:00:00 +0100 5568545 http://www.medworm.com/index.php?rid=5512095&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111796 Plastoquinone-9 (PQ-9) has a central role in the energy transformation processes in cyanobacteria by mediating electron transfer in both, the photosynthetic as well as the respiratory electron transport chain. The present study provides evidence that the PQ-9 biosynthetic pathway in cyanobacteria substantially differs from that in plants. We identified 4-hydroxybenzoate as being the aromatic precursor for PQ-9 in Synechocystis sp. PCC6803 and report here on the role of the membrane-bound 4-hydroxybenzoate solanesyltransferase, Slr0926, in PQ-9 biosynthesis and on the properties of the enzyme. The catalytic activity of Slr0926 was demonstrated by in vivo labelling experiments in Synechocystis sp., complementation studies in an E. coli mutant with a defect in ubiquinone biosynthesis as well ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5512095 Wed, 14 Dec 2011 05:00:00 +0100 5512095 http://www.medworm.com/index.php?rid=5492382&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111311 Iron is an essential micronutrient that acts as a cofactor in a wide variety of pivotal metabolic processes, such as electron transport chain of respiration, photosynthesis, and redox reactions, in plants. However, its overload exceeding the cellular capacity of iron binding and storage is potentially toxic to plant cells by causing oxidative stress and cell death. Consequently, plants have developed versatile mechanisms to maintain iron homeostasis. Organismal iron content is tightly regulated at the steps of uptake, translocation, and compartmentalization. Whereas iron uptake is fairly well understood at the cellular and organismal levels, intracellular and intercellular transport is only poorly understood. Here, we show that a multidrug and toxic compound extrusion (MATE) transporter, d... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5492382 Thu, 08 Dec 2011 05:00:00 +0100 5492382 http://www.medworm.com/index.php?rid=5473458&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111443 The genes for 2-carboxy-D-arabinitol 1-phosphate phosphatase (CA1P phosphatase) from French bean, wheat, Arabidopsis and tobacco were identified and cloned. The deduced protein sequence included an N-terminal motif identical to the phosphogycerate mutase (PGM) active site sequence [LIVM]-x-R-H-G-[EQ]-x-x-[WN]. The corresponding gene from wheat coded for an enzyme with the properties published for CA1P phosphatase. The expressed protein lacked PGM activity but rapidly dephosphorylated 2,3-diphosphoglycerate to 3-phosphoglycerate. DTT activation and GSSG inactivation of this enzyme was pH sensitive, the greatest difference being apparent at pH 8. The presence of the expressed protein during in vitro measurement of Rubisco carboxylase activity prevented a progressive decline in Rubisco turnov... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5473458 Fri, 02 Dec 2011 05:00:00 +0100 5473458 http://www.medworm.com/index.php?rid=5464994&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111378 This study establishes the capacity of this Cys-Gpx to reduce peroxynitrite with a catalytic efficiency of 106 M-1 s-1. In PtGpx5, Glu79, which replaces the Gln usually found in Gpx catalytic tetrad, is likely involved in substrate selectivity. Although the redox midpoint potential of the Cys44-Cys92 disulfide and the pKa of Cys44 are not modified in the E79Q variant, it exhibited significantly improved kinetic parameters (Kperoxide and kcat) with tert-butyl hydroperoxide. The characterization of the monomeric Y151R variant demonstrated that PtGpx5 is not an obligate homodimer. Also, we show that the conserved Phe90 is important for Trx recognition and that Trx-mediated recycling of PtGpx5 occurs via the formation of a transient disulfide between the Trx catalytic cysteine and the Gpx5 res... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5464994 Tue, 29 Nov 2011 05:00:00 +0100 5464994 http://www.medworm.com/index.php?rid=5396488&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111498 The uptake of potassium ions (K+) accompanied by an acidification of the apoplasm is a prerequisite for stomatal opening. The acidification (around 2-2.5 pH units) is perceived by voltage gated inward potassium channels (Kin) that then can open their pores with lower energy cost. The sensory units for extracellular pH in stomatal Kin channels are proposed to be histidines exposed to the apoplasm. However, in the Arabidopsis thaliana stomatal Kin channel KAT1, mutations in the unique histidine (H267) exposed to the solvent, do not affect the pH dependency. We demonstrate here that H267 of the KAT1 channel cannot sense pH changes since the neighboring residue F266 shifts its pKa to undetectable values through a cation-pi interaction. Instead, we show that residue E240 placed in the ex... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5396488 Thu, 10 Nov 2011 05:00:00 +0100 5396488 http://www.medworm.com/index.php?rid=5330242&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111170 The molybdenum cofactor sulfurase ABA3 from Arabidopsis thaliana catalyzes the sulfuration of the molybdenum cofactor of aldehyde oxidase and xanthine oxidoreductase, which represents the final activation step of these enzymes. ABA3 consists of an N-terminal NifS-like domain that exhibits L-cysteine desulfurase activity, and a C-terminal domain that binds sulfurated molybdenum cofactor. The strictly conserved cysteine430 in the NifS-like domain binds a persulfide intermediate, which is abstracted from the substrate L-cysteine and finally needs to be transferred to the molybdenum cofactor of aldehyde oxidase and xanthine oxidoreductase. In addition to cysteine430, another eight cysteine residues are located in the NifS-like domain, with two of them being highly conserved among molybdenum co... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5330242 Mon, 17 Oct 2011 04:00:00 +0100 5330242 http://www.medworm.com/index.php?rid=5301651&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111199 In this study, a fusion gene containing the VP from Pleurotus eryngii was subjected to six rounds of directed evolution, achieving a level of secretion in Saccharomyces cerevisiae (21 mg/L) as yet unseen for any ligninolytic peroxidase. The evolved variant for expression harboured 4 mutations and increased its total VP activity 129-fold. The signal leader processing by the STE13 protease at the Golgi compartment changed as consequence of over-expression, retaining the additional N-terminal sequence EAEA that enhanced secretion. The engineered N-terminal truncated variant displayed similar biochemical properties as the non-truncated counterpart in terms of kinetics, stability and spectroscopic features. Additional cycles of evolution raised the T50 8ºC and significantly increased the... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5301651 Fri, 07 Oct 2011 04:00:00 +0100 5301651 http://www.medworm.com/index.php?rid=5155306&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20110776 We describe here a novel class of PTEN proteins in plants, termed PTEN2, which comprises the AtPTEN2a and AtPTEN2b proteins in Arabidopsis. Both display low in vitro tyrosine phosphatase activity. In addition, AtPTEN2a actively dephosphorylates in vitro the 3’phosphate group of PI3P, PI(3,4)P2, and PI(3,5)P2. In contrast to the animal PTENs, the PI(3,4,5)P3 is a poor substrate. Site-directed mutagenesis of AtPTEN2a and molecular modeling of protein-phosphoinositide interactions indicated that substitutions at the PTEN2 core catalytic site of the K267 and G268 residues found in animals, and which are critical for animal PTEN activity, by the M267 and A268 residues found in the eudicot PTEN2 are responsible for changes in substrate specificity. Remarkably, the AtPTEN2a protein also di... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5155306 Tue, 23 Aug 2011 23:00:00 +0100 5155306 http://www.medworm.com/index.php?rid=5155307&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20111112 Binding of specific microbial epitopes (microbe-associated molecular patterns, MAMPs) to pattern recognition receptors (PRRs) and subsequent receptor kinase activation are key steps in plant innate immunity. One of the earliest detectable events after MAMP perception is a rapid and transient rise in cytosolic calcium (Ca2+) levels. In plants, knowledge about the signaling events leading to Ca2+ influx and on the molecular identity of the channels involved is scarce. We used a transgenic Arabidopsis thaliana line stably expressing the luminescent aequorin Ca2+ biosensor to monitor pharmacological interference with Ca2+ signatures following treatment with the bacterial peptide MAMPs flg22 and elf18 and the fungal carbohydrate MAMP chitin. Using a comprehensive set... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5155307 Wed, 17 Aug 2011 23:00:00 +0100 5155307 http://www.medworm.com/index.php?rid=5137674&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20110939 L-Ascorbate catabolism involves reversible oxidation to dehydroascorbic acid (DHA), then irreversible oxidation or hydrolysis. The precursor–product relationships and the identity of several major DHA breakdown products remained unclear. In the presence of added H2O2, DHA underwent little hydrolysis to 2,3-diketogulonate (DKG). Instead it yielded oxalyl-threonate (OxT2-), cyclic-oxalyl-threonate (cOxT-) and free oxalate (~6:1:1), essentially simultaneously, suggesting that all three product classes independently arose from one reactive intermediate, proposed to be cyclic-2,3-O-oxalyl-L-threonolactone. Only with plant apoplastic esterases present were the esters significant precursors of free oxalate. Without added H2O2, DHA was slowly hydrolysed to DKG. Downstream of DKG was a singl... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5137674 Tue, 16 Aug 2011 23:00:00 +0100 5137674 http://www.medworm.com/index.php?rid=5048046&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20110536 PII proteins belong to a family of highly conserved signal transduction proteins widely spread in bacteria, archaea and plants. They respond to the central metabolites ATP, ADP and 2-oxoglutarate (2-OG) and control enzymes, transcription factors and transport proteins involved in nitrogen metabolism. Here we studied the effect of ADP on in vitro PII signalling properties from the cyanobacterium Synechococcus elongatus, a model for oxygenic phototrophic organisms. Different ADP/ATP ratios strongly affected the properties of PII signalling. Increasing ADP antagonized the binding of 2-oxoglutarate and directly affected the interactions of PII with its target proteins. The resulting PII signalling properties indicate that in mixtures of ADP and ATP, PII trimers are occupied with mixtures of ad... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5048046 Wed, 20 Jul 2011 23:00:00 +0100 5048046 http://www.medworm.com/index.php?rid=5017640&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20110845 Stomatal guard cells play a key role in gas exchange for photosynthesis and in minimizing transpirational water loss from plants by opening and closing the stomatal pore. The bulk of the osmotic content driving stomatal movements depends on ionic fluxes across both the plasma membrane and tonoplast, the metabolism of organic acids, primarily malate (Mal), its accumulation and loss. Anion channels at the plasma membrane are thought to comprise a major pathway for Mal efflux during stomatal closure, implicating their key role in linking solute flux with metabolism. Nonetheless, little is known of the regulation of anion channel current (ICl) by cytosolic malate or its immediate metabolite oxaloacetate (OAA). We have examined the impact of Mal, OAA, and of the monocarboxylic acid anion acetat... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5017640 Sun, 10 Jul 2011 23:00:00 +0100 5017640 http://www.medworm.com/index.php?rid=5006156&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20110814 Phycoerythrobilin (PEB) is one of the major open-chain tetrapyrrole molecules found in cyanobacterial light-harvesting phycobiliproteins. In these organisms, two enzymes of the ferredoxin-dependent bilin reductase family work in tandem to reduce biliverdin IXa to PEB. In contrast, a single cyanophage-encoded enzyme of the same family has been identified to catalyze the identical reaction. Using UV-Vis and EPR spectroscopy we investigated the two individual cyanobacterial enzymes PebA and PebB showing that the two subsequent reactions catalyzed by the phage enzyme PebS are clearly dissected in the cyanobacterial versions. While a highly conserved aspartate residue is critical for both reductions, a second conserved aspartate is only involved in the A-ring reduction of the tetrapyrrole in Pe... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5006156 Mon, 04 Jul 2011 23:00:00 +0100 5006156 http://www.medworm.com/index.php?rid=4891404&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101884 The plant-specific phi class of glutathione transferases (GSTFs) are often highly stress-inducible and expressed in a tissue-specific manner, suggestive of them having important protective roles. To date, these functions remain largely unknown, although activities associated with the binding and transport of reactive metabolites have been proposed. Using a sensitive and selective binding screen, we have probed the Arabidopsis thaliana GSTFs for natural product ligands from bacteria and plants. Uniquely, when over-expressed in bacteria, family members GSTF2 and GSTF3 bound a series of heterocyclic compounds including lumichrome, harmane, norharmane and indole-3-aldehyde. When screened against total metabolite extracts from A. thaliana, GSTF2 also selectively bound the indole-derived phytoal... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4891404 Tue, 31 May 2011 23:00:00 +0100 4891404 http://www.medworm.com/index.php?rid=5006157&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20110025 APR2 is the dominant adenosine 5'-phosphosulfate reductase in the model plant Arabidopsis thaliana, and converts activated sulfate to sulfite, a key reaction in the sulfate reduction pathway. To determine if APR2 has a role in selenium tolerance and metabolism, a mutant Arabidopsis line (apr2-1) was studied. apr2-1 plants had decreased selenate tolerance and photosynthetic efficiency. Sulfur metabolism was perturbed in apr2-1 plants grown on selenate, as observed by an increase in total sulfur and sulfate, and a two-fold decrease in glutathione concentration. The altered sulfur metabolism in apr2-1 grown on selenate did not reflect typical sulfate starvation, as cysteine and methionine levels were increased. Knockout of APR2 also increased the accumulation of total selenium and selenate. H... BJ Plant journals http://www.medworm.com/rss/comments.php?id=5006157 Mon, 16 May 2011 23:00:00 +0100 5006157 http://www.medworm.com/index.php?rid=4839443&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20110025 APR2 is the dominant adenosine 5'-phosphosulfate reductase in the model plant Arabidopsis thaliana, and converts activated sulfate to sulfite, a key reaction in the sulfate reduction pathway. To determine if APR2 has a role in selenium tolerance and metabolism, a mutant Arabidopsis line (apr2-1) was studied. apr2-1 plants had decreased selenate tolerance and photosynthetic efficiency. Sulfur metabolism was perturbed in apr2-1 plants grown on selenate, as observed by an increase in total sulfur and sulfate, and a two-fold decrease in glutathione concentration. The altered sulfur metabolism in apr2-1 grown on selenate did not reflect typical sulfate starvation, as cysteine and methionine levels were increased. Knockout of APR2 also increased the accumulation of total selenium and selenate. H... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4839443 Mon, 16 May 2011 23:00:00 +0100 4839443 http://www.medworm.com/index.php?rid=4811819&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101764 ACETATE NON-UTILIZING 1 (ACN1) is a short-chain acyl-CoA synthetase, which activates acetate to acetyl-CoA in peroxisomes of Arabidopsis. Pulse-chase [2-13C]acetate feeding of the mutant acn1-2 revealed that acetate accumulation and assimilation were no different to that of wild-type, Col-7. However, the lack of acn1-2 led to a decrease of nearly 50% in 13C-labelling of glutamine, a major carbon sink in seedlings, and large decreases in primary metabolite levels. In contrast, acetyl-CoA levels were higher in acn1-2 compared to Col-7. The disappearance of eicosenoic acid was slightly delayed in acn1-2 indicating only a small effect on the rate of lipid breakdown. A comparison of transcript levels in acn1-2 and col-7 showed that induced genes included a number of metabolic genes and also a l... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4811819 Tue, 10 May 2011 23:00:00 +0100 4811819 http://www.medworm.com/index.php?rid=4692388&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20110180 We determined characteristic repeat distances of the photosynthetic membranes in living cyanobacterial and eukaryotic algal cells and in intact thylakoid membranes isolated from higher plants with time-resolved small-angle neutron scattering. This non-invasive technique reveals light-induced reversible reorganizations in the seconds to minutes time scale, which appear to be associated with functional changes in vivo. (Source: BJ Plant) BJ Plant journals http://www.medworm.com/rss/comments.php?id=4692388 Thu, 07 Apr 2011 23:00:00 +0100 4692388 http://www.medworm.com/index.php?rid=4621384&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20110299 The desire for improved methods of biomass conversion to fuels and feedstocks has re-awakened interest in the enzymology of plant cell wall degradation. The complex polysaccharide xyloglucan is abundant in plant matter, where it may account for up to 20% of the total primary cell wall carbohydrates. Despite this, few studies have focussed on xyloglucan saccharification, which requires a consortium of enzymes including endo-xyloglucanases, α-xylosidases, β‑galactosidases and α-l-fucosidases, among others. Here, we present the characterisation of Xyl31A, a key α-xylosidase in xyloglucan utilisation by the model Gram-negative soil saprophyte Cellvibrio japonicus. CjXyl31A exhibits high regiospecificity for the hydrolysis xylogluco-oligosaccharides, with a pa... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4621384 Tue, 22 Mar 2011 00:00:00 +0100 4621384 http://www.medworm.com/index.php?rid=4488659&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101429 The evolution of natural products biosynthetic pathways can be envisioned to occur via a number of mechanisms. Here we provide evidence that latent plasticity plays a role in such metabolic evolution. In particular, rice (Oryza sativa) produces both ent- and syn- copalyl diphosphate (CPP), which are substrates for downstream diterpene synthases. Here we report that several members of this enzymatic family exhibit dual reactivity with some pairing of ent-, syn-, or normal CPP stereochemistry. Evident plasticity was observed, as a previously reported ent-sandaracopimaradiene synthase also converts syn-CPP to syn-labda-8(17),12E,14-triene, which can be found in planta. Notably, normal CPP is not naturally found in rice. Thus, the presence of diterpene synthases that react with this non-native... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4488659 Wed, 16 Feb 2011 00:00:00 +0100 4488659 http://www.medworm.com/index.php?rid=4481877&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101941 The phytohormone gibberellin and the DELLA proteins act together to control key aspects of plant development. Gibberellin induces degradation of DELLA proteins by recruitment of an F-box protein, using a molecular switch: a gibberellin-bound nuclear receptor interacts with the N-terminal domain of DELLA proteins, and this event primes the DELLA C-terminal domain for interaction with the F-box protein. However, the mechanism of signalling between the N- and C-terminal domains of DELLA proteins is unresolved. We used in vivo and in vitro approaches to characterise two- and three-partite interactions of the DELLA protein RGL1 of Arabidopsis thaliana with the gibberellin receptor GID1A and the F-box protein SLY1. Deuterium exchange mass spectroscopy unequivocally showed that the RGL1 entire N-... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4481877 Tue, 15 Feb 2011 00:00:00 +0100 4481877 http://www.medworm.com/index.php?rid=4423506&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101610 GSTZs (zeta class glutathione transferases) are multifunctional enzymes that belong to a highly conserved subfamily of soluble GSTs found in species ranging from fungi and plants to animals. GSTZs are known to function as MAAIs (maleylacetoacetate isomerases), which play a role in tyrosine catabolism by catalyzing the isomerization of MAA (maleylacetoacetate) to FAA (fumarylacetoacetate). As tyrosine metabolism in plants differs from animals, the significance of GSTZ/MAAI is unclear. In rice (Oryza sativa L.), a major QTL for seedling cold tolerance has been fine mapped to a region containing the genes OsGSTZ1 and OsGSTZ2. Sequencing of tolerant (ssp. japonica cv. M-202) and sensitive (ssp. indica cv. IR50) cultivars revealed two SNP (single nucleotide polymorphisms) in OsGSTZ2 that result... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4423506 Tue, 01 Feb 2011 00:00:00 +0100 4423506 http://www.medworm.com/index.php?rid=4370201&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101613 In this study, we investigate the oligomerisation behaviour of this unusual protease by yeast two-hybrid analysis in vivo and with recombinant protein in vitro. We show that DEG7 forms trimeric complexes, but in contrast to other known Deg/HtrA proteases it shows a new principle of oligomerisation, where trimerisation is based on the interactions between degenerated protease domains. We propose that during evolution a duplicated active protease domain degenerated and specialised on protein-protein interaction and complex formation. (Source: BJ Plant) BJ Plant journals http://www.medworm.com/rss/comments.php?id=4370201 Wed, 19 Jan 2011 00:00:00 +0100 4370201 http://www.medworm.com/index.php?rid=4360086&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101019 The TCP domain is a DNA binding domain present in plant transcription factors that modulate different processes. We show here that Arabidopsis class I TCP proteins are able to interact with a dyad-symmetric sequence composed of two GTGGG half-sites. TCP20 establishes symmetric interactions with the 5’ half of each strand, while TCP11 interacts mainly with the 3’ half. SELEX experiments with TCP15 and TCP20 indicated that these proteins have similar, though not identical, DNA binding preferences and are able to interact with non-palindromic binding sites of the type GTGGGNCCNN. TCP11 shows a different DNA binding specificity, with a preference for the sequence GTGGGCCNNN. The distinct DNA binding properties of TCP11 are due to the presence of threonine at position 15 of the TC... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4360086 Mon, 17 Jan 2011 00:00:00 +0100 4360086 http://www.medworm.com/index.php?rid=4336917&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101035 Protein phosphatase one (PP1) is among the most conserved enzymes known, with one or more isoforms present in sequenced eukaryotic genomes. PP1 dephosphorylates specific serine/ threonine phosphoproteins as defined by associated regulatory or targeting subunits. We performed a PP1 binding screen to find putative PP1 interactors in Arabidopsis thaliana and uncovered a homolog of the ancient PP1 interactor, inhibitor-2 (I-2). Bioinformatic analysis revealed remarkable conservation of three regions of plant I-2 that play key roles in binding and regulating PP1 function. The sequence-related properties of plant I-2 were compared across eukaryotes and reveal the absence of I-2 in some species and where key motifs likely emerged during the evolution of this ancient regulator. Biochemical charact... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4336917 Tue, 11 Jan 2011 00:00:00 +0100 4336917 http://www.medworm.com/index.php?rid=4132307&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101642 Phycoerythrobilin (PEB) is a pink-colored open-chain tetrapyrrole molecule found in the cyanobacterial light-harvesting phycobilisome. Within the phycobilisome, PEB is covalently bound via thioether bonds to conserved cysteine residues of the phycobiliprotein subunits. In cyanobacteria, biosynthesis of PEB proceeds via two subsequent two-electron reductions catalyzed by the ferredoxin-dependent bilin reductases (FDBR) PebA and PebB starting from the open-chain tetrapyrrole biliverdin IXalpha. Recently, a new member of the FDBR family was identified in the genome of a marine cyanophage. In contrast to the cyanobacterial enzymes, PEB-synthase (PebS) from cyanophage combines both two-electron reductions for PEB synthesis. Here we show that PebS acts via a substrate radical mechanism and that ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4132307 Thu, 04 Nov 2010 00:00:00 +0100 4132307 http://www.medworm.com/index.php?rid=4072826&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20101361 PEPC [PEP (phosphoenolpyruvate) carboxylase] is a tightly controlled anaplerotic enzyme situated at a pivotal branch point of plant carbohydrate -metabolism. Two distinct oligomeric PEPC classes were discovered in developing castor oil seeds (COS). Class-1 PEPC is a typical homotetramer of 107-kDa plant-type PEPC (PTPC) subunits, whereas the novel 910-kDa Class-2 PEPC hetero-octamer arises from a tight interaction between Class-1 PEPC and 118-kDa bacterial-type PEPC (BTPC) subunits. Mass spectrometric analysis of immunopurified COS BTPC indicated that it is subject to in vivo Pro-directed phosphorylation at S425. Here, immunoblots probed with phosphorylation site-specific antibodies demonstrated that S425 phosphorylation is promoted during COS development, becoming maximal at stage IX (mat... BJ Plant journals http://www.medworm.com/rss/comments.php?id=4072826 Thu, 14 Oct 2010 23:00:00 +0100 4072826 http://www.medworm.com/index.php?rid=3857619&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20100597 Kaurene oxidase (KO) is a multifunctional cytochrome P450 catalyzing three sequential oxidations in gibberellin phytohormone biosynthesis. These serve to transform the C4a methyl of the ent-kaurene olefin intermediate into the carboxylic acid moiety of ent-kauren-19-oic acid. To investigate the unknown catalytic mechanism and properties of KO, we have engineered the corresponding CYP701A3 from Arabidopsis thaliana (AtKO) for functional recombinant expression in E. coli, involving use of a fully codon-optimized construct, along with additional N-terminal deletion and modification. This recombinant AtKO (rAtKO) was used to carry out 18O2 labeling studies with ent-kaurene, and the intermediates ent-kaurenol and ent-kaurenal, to investigate the multifunctional reaction sequence; revealing cata... BJ Plant journals http://www.medworm.com/rss/comments.php?id=3857619 Tue, 10 Aug 2010 23:00:00 +0100 3857619 http://www.medworm.com/index.php?rid=3647851&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20100497 The Arabidopsis thaliana genome contains two genes encoding NAD-malic enzymes (NAD-ME1, At4G13560 and NAD-ME2, At4G00570). The encoded proteins are localized to mitochondria and assemble as homo- and heterodimers in vitro and in vivo. In this work, the kinetic mechanisms of NAD-ME1 and -2 homodimers and the heterodimer (NAD-MEH) were studied as an approach to understand the contribution of these enzymes to the plant physiology. Product inhibition and substrate analogue analyses indicated that NAD-ME2 follows a sequential ordered Bi-Ter mechanism, being NAD the leading substrate followed by L-malate. On the other hand, NAD-ME1 and NAD-MEH can bind both substrates randomly. However, NAD-ME1 shows a preferred route that involves the addition of NAD in the first place. As a consequence of the ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=3647851 Tue, 08 Jun 2010 23:00:00 +0100 3647851 http://www.medworm.com/index.php?rid=3624742&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20100566 Serine hydroxymethyltransferase (SHMT, EC 2.1.2.1) catalyses reversible hydroxymethyl-group transfer from serine to tetrahydrofolate (H4PteGlun), yielding glycine and 5,10-methylenetetrahydrofolate. In plastids, SHMTs are thought to catalytically direct the hydroxymethyl moiety of serine into the metabolic network of H4PteGlun-bound one-carbon units. Genes encoding putative plastid SHMTs were found in genomes of various plant species. SHMT activity was detected in chloroplasts in pea (Pisum sativum) and barley (Hordeum vulgare), suggesting that plastid SHMTs exist in all flowering plants. The Arabidopsis thaliana genome encodes one putative plastid SHMT (AtSHMT3). Its cDNA was cloned by reverse transcription-PCR and the encoded recombinant protein was produced in Escherichia coli. Evidence... BJ Plant journals http://www.medworm.com/rss/comments.php?id=3624742 Wed, 02 Jun 2010 23:00:00 +0100 3624742 http://www.medworm.com/index.php?rid=3533124&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20100291 An extracellular form of the Ca2+-dependent protein-cross-linking enzyme transglutaminase (TGase) was demonstrated to be involved in the apical growth of Malus domestica pollen tube. Apple pollen transglutaminase and its substrates were co-localized within aggregates on the pollen tube surface, as determined by indirect immuno-fluorescence staining and the in situ cross-linking of fluorescently labeled substrates. Transglutaminase-specific inhibitors and an anti-TGase monoclonal antibody blocked pollen tube growth, whereas incorporation of a recombinant fluorescent mammalian TGase substrate (histidine-tagged green fluorescent protein: His6-Xpr-GFP) into the growing tube wall enhanced tube length and germination, consistent with a role of TGase as modulator of cell wall building and ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=3533124 Tue, 04 May 2010 23:00:00 +0100 3533124 http://www.medworm.com/index.php?rid=3475189&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20100492 Several studies focused on elucidating the mechanism of nitric oxide (NO) signalling in plant cells highlighted that its biological effects are partly mediated by protein kinases. Identity of these kinases and details of how NO modulates their activities, however, remain poorly investigated. Here, we have attempted to clarify the mechanisms underlying NO action in regulation of Nicotiana tabacum osmotic stress-activated protein kinase (NtOSAK), a member of the SNF1-related protein kinase 2 family. We found that in tobacco BY-2 cells exposed to salt stress, NtOSAK is rapidly activated partly through a NO-dependent process. This activation, as well as the one observed following treatment of BY-2 cells with the NO donor DEA/NO, involved the phosphorylation of two residues located in the kinas... BJ Plant journals http://www.medworm.com/rss/comments.php?id=3475189 Thu, 15 Apr 2010 23:00:00 +0100 3475189 http://www.medworm.com/index.php?rid=3377654&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20091777 In this report the allosteric contributions of the different large subunits were compared by expressing each one in E. coli, in conjunction with S and individually, and characterizing the resulting enzyme activity. Our results indicate different kinetic characteristics of the tomato L1/S and L3/S heterotetramers. Surprisingly, the recombinant L3 protein was also active when expressed alone and size exclusion and immunoblotting showed that it functioned as a monomer. Subunit interaction modeling pointed to two amino acids potentially affecting subunit interactions. However, directed mutations did not impact on subunit tetramerization. These results indicate a hitherto unknown active role for the large subunit in the synthesis of ADP-Glc. (Source: BJ Plant) BJ Plant journals http://www.medworm.com/rss/comments.php?id=3377654 Wed, 17 Mar 2010 00:00:00 +0100 3377654 http://www.medworm.com/index.php?rid=3301491&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20091878 The endoplasmic reticulum (ER) has long been considered the plant cell compartment within which protein disulfide bond formation occurs. Members of the ER-located protein disulfide isomerase (PDI) family are responsible for oxidising, reducing and isomerising disulfide bonds, as well as functioning as chaperones to newly synthesised proteins. Here we demonstrate that an abundant 7S lectin of the castor oil seed protein storage vacuole, Ricinus communis agglutinin 1 (RCA), is folded in the ER as disulfide bonded A-B dimers in both vegetative cells of tobacco leaf and in castor oil seed endosperm, but that these assemble into (A-B)2 disulfide-bonded tetramers only after Golgi-mediated delivery to the storage vacuoles in the producing endosperm tissue. These observations reveal an alternative... BJ Plant journals http://www.medworm.com/rss/comments.php?id=3301491 Wed, 24 Feb 2010 00:00:00 +0100 3301491 http://www.medworm.com/index.php?rid=3275324&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20091762 Changes in membrane fluidity are the earliest cellular events that occur in plant cells upon exposure to cold. This subsequently triggers physiological processes, such as calcium influx and reorganization of actin cytoskeletons, and induces expression of cold-responsive genes. The plasma membrane-anchored NAC transcription factor NTL6 is of particular interest. Cold triggers proteolytic activation of the dormant NTL6 protein, which in turn elicits pathogen resistance responses by inducing a small group of cold-inducible Pathogenesis-Related (PR) genes in Arabidopsis. Here, we show that proteolytic processing of NTL6 is regulated by cold-induced remodeling of membrane fluidity. NTL6 processing was stimulated rapidly by cold. The protein stability of NTL6 was also enhanced by cold. The effec... BJ Plant journals http://www.medworm.com/rss/comments.php?id=3275324 Tue, 16 Feb 2010 00:00:00 +0100 3275324 http://www.medworm.com/index.php?rid=3258184&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20100015 In this study, protein degradation is found to occur in purified soybean seed ferritin (SSF) (consisting of H-1 and H-2 subunits) during storage, consistent with previous results that such degradation also occurs during seedling germination. In contrast, no degradation is observed with animal ferritin under identical conditions, suggesting that SSF auto-degradation might be due to the extension peptide (EP) on the exterior surface of protein, a specific domain found only in phytoferritin. Indeed, EP-deleted SSF becomes stable, confirming the above mentioned idea. Further support comes from a protease activity assay showing that EP-1 (corresponding to the EP of the H-1 subunit) exhibits significant serine protease-like activity, while the activity of EP-2 (corresponding to the EP of the H-2... BJ Plant journals http://www.medworm.com/rss/comments.php?id=3258184 Wed, 10 Feb 2010 00:00:00 +0100 3258184 http://www.medworm.com/index.php?rid=3066373&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20091234 In conclusion, our results demonstrate that biochemical and functional specificity is associated with both DBDs and TRDs in NAC TFs. (Source: BJ Plant) BJ Plant journals http://www.medworm.com/rss/comments.php?id=3066373 Tue, 08 Dec 2009 00:00:00 +0100 3066373 http://www.medworm.com/index.php?rid=2942972&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20091096 In Aspergillus nidulans psi factor producing oxygenases (Ppos) are required for the production of so-called psi factors (precocious sexual inducer) - compounds that control balance between the sexual and asexual life cycle of the fungus. The genome of A. nidulans harbours three different ppo genes: ppoA, ppoB and ppoC. For all three enzymes two different heme containing domains are predicted: a fatty acid heme peroxidase/dioxygenase domain for the N-terminal region and a P450 heme thiolate domain for the C-terminal region. While PpoA was shown to use both heme domains for its bifunctional catalytic activity (linoleic acid 8-dioxygenation and 8-hydroperoxide isomerisation), we found that PpoC apparently only harbours a functional heme peroxidase/dioxygenase domain. Consequently, we observed... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2942972 Fri, 30 Oct 2009 00:00:00 +0100 2942972 http://www.medworm.com/index.php?rid=2838568&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20091221 In this study, we have demonstrated that the carboxyl-terminus region of KAT1 acts as a phosphorylation target for the Arabidopsis calcium-independent, ABA-activated protein kinase SnRK2.6. This was confirmed by LC-MS/MS analysis, which showed that KAT1 Thr306 and Thr308 residues were modified by phosphorylation. The role of these specific residues was examined by single point mutation and measurement of KAT1 channel activities in Xenopus oocyte and yeast systems. Modification of Thr308 had minimal effect on KAT1 activity. On the other hand, modification of Thr306 reduced K+ transport uptake activity of KAT1 in both systems, indicating that Thr306 is responsible for the functional regulation of KAT1. This data suggests that negative regulation of KAT1 activity required for stomatal ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2838568 Sun, 27 Sep 2009 23:00:00 +0100 2838568 http://www.medworm.com/index.php?rid=2814146&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20091102 Genetic studies have identified the membrane protein Ethylene Insensitive 2 (EIN2) as a central component of ethylene signalling in Arabidopsis. In addition, EIN2 might take part in multiple hormone signalling pathways and in responses to pathogens as demonstrated by recent genetic and biochemical studies. Here we show, by an integrated approach of in vivo and in vitro fluorescence techniques, that EIN2 is localised at the ER membrane where it shows specific interaction with the ethylene receptor protein ETR1. (Source: BJ Plant) BJ Plant journals http://www.medworm.com/rss/comments.php?id=2814146 Sun, 20 Sep 2009 23:00:00 +0100 2814146 http://www.medworm.com/index.php?rid=2795919&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20091025 UDP-sugars serve as substrates in the synthesis of cell wall polysaccharides and are themselves generated through sequential interconversion reactions from UDP-glucose (UDP-Glc) as the starting substrate in the cytosol and the Golgi apparatus. For this study, a soluble enzyme with UDP-xylose (UDP-Xyl) 4-epimerase activity was purified about 300-fold from pea (Pisum sativum L.) sprouts by conventional chromatography. The N-terminal amino acid sequence of the enzyme revealed that it is encoded by a predicted UDP-Glc 4-epimerase gene, PsUGE1, and distinct from UDP-Xyl 4-epimerase localized in the Golgi apparatus. Recombinant PsUGE1 (rPsUGE1) expressed in Escherichia coli exhibited both UDP-Xyl 4-epimerase and UDP-Glc 4-epimerase activities with apparent Km values of 0.31, 0.29, 0.16, and 0.15... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2795919 Mon, 14 Sep 2009 23:00:00 +0100 2795919 http://www.medworm.com/index.php?rid=2756941&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20090620 L-Phenylalanine ammonia-lyase (PAL), the first enzyme of phenylpropanoid biosynthesis, is often encoded by multigene families in plants. A PCR-based approach was used to isolate cDNA clones corresponding to the four PAL genes of tobacco (Nicotiana tabacum). By careful comparison of cDNA and genomic clones, a new PAL gene (PAL4) was defined. PCR-amplification of PAL sequences from cDNA led to the generation of chimeric clones between PAL1 and PAL4, and incorrect annotation of PAL4 ESTs as PAL1 in the EST database has given rise to a randomly shuffled tentative consensus sequence. The PAL2 previously described in the literature was shown, by domain swapping experiments with PAL1, to possess a single nucleotide substitution leading to an inactive enzyme. The altered amino acid resulting from ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2756941 Tue, 01 Sep 2009 23:00:00 +0100 2756941 http://www.medworm.com/index.php?rid=2733526&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20090785 Lipid droplets (LDs) are cellular organelles which can be found in nearly all eukaryotic cells. Despite their importance in cell biology as highlighted by their implication in many devastating diseases, the mechanism underlying LD biogenesis remains largely unknown. Here we report that conditions of endoplasmic reticulum (ER) stress stimulate LD formation in Saccharomyces cerevisiae. We found that LDs accumulated in yeast mutants with compromised protein glycosylation or ER-associated protein degradation. Moreover, Tunicamycin and Brefeldin A, agents which induce ER stress were found to stimulate LD formation. In contrast the restoration of protein glycosylation reduced LD accumulation. Interestingly, enhanced neutral lipids synthesis and LD formation under conditions of ER stress was not ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2733526 Tue, 25 Aug 2009 23:00:00 +0100 2733526 http://www.medworm.com/index.php?rid=2719189&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20091023 In this report on GCP1-type proteins from eukaryotic organisms we demonstrate that GCP1 is a mitochondrial protein in Homo sapiens (called here GCP1/OSGEPL1) and Arabidopsis thaliana that is located/anchored to the inner mitochondrial membrane. Analysis of mRNA and protein levels revealed that the expression of GCP1/OSGEPL1 in A. thaliana and H. sapiens is tissue- and organ-specific and depends on developmental stage, suggesting a more specialized function for this protein. We show that homozygous A. thaliana GCP1 T-DNA insertion lines are embryo-lethal. Embryos in homozygous seeds are arrested at the globular stage and fail to undergo the transition to heart stage. Based on this data we propose that the mitochondrial GCP1 is essential for embryo development in plants. (Source: BJ Plant) BJ Plant journals http://www.medworm.com/rss/comments.php?id=2719189 Thu, 20 Aug 2009 23:00:00 +0100 2719189 http://www.medworm.com/index.php?rid=2625204&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20090581 Plant nitrite reductase (NiR) and sulfite reductase (SiR) have common features in structure and function. Both enzymes are generally distinguished in terms of substrate specificity for nitrite and sulfite. The Cyanidioschyzon merolae genome encodes two SiR homologs (CmSiRA and CmSiRB), but no NiR homolog. The facts that most known SiRs have a low nitrite-reducing activity and that CmSiRB is mapped between the genes for nitrate transporter and nitrate reductase implied that CmSiRB could have a potential function as a nitrite-reducing enzyme. To verify this hypothesis, we produced a recombinant form of CmSiRB and characterized its enzymatic properties. The enzyme was found to have a significant nitrite reduction activity, while sulfite reduction activity was extremely low. As the affinity of... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2625204 Mon, 20 Jul 2009 23:00:00 +0100 2625204 http://www.medworm.com/index.php?rid=2503398&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20090655 Natural Resistance Associated Macrophage Protein (NRAMP) homologues are evolutionarily conserved divalent metal transporters. In Arabidopsis, AtNRAMP3 and AtNRAMP4 play a key role in iron nutrition of the germinating plantlet by remobilizing vacuolar Fe stores. Here we describe the molecular and physiological characterization of AtNRAMP6. AtNRAMP6 is predominantly expressed in the dry seed embryo and to a lesser extent in aerial parts. Its promoter activity is found diffusely distributed in cotyledons and hypocotyls as well as in the vascular tissue region of leaf and flower. We show that AtNRAMP6 transcript coexists with a partially spliced isoform in all tested shoot cell types. When expressed in yeast, AtNRAMP6, but not its misspliced derivative, increased sensitivity to cadmium without... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2503398 Sun, 21 Jun 2009 23:00:00 +0100 2503398 http://www.medworm.com/index.php?rid=2396665&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20082020 In this study, a cotton kinesin GhKCH2, which contains a calponin homology (CH) domain at the N-terminus, was analyzed in vitro and in vivo to understand its interaction with the two cytoskeletal elements. A specific antibody to GhKCH2 was prepared and used for immunolabeling experiments. Some GhKCH2 spots appeared along a few microtubules and microfilaments in developing cotton fibers. His-tagged N-terminus of GhKCH2 (GhKCH2-N) could coprecipitate with microfilaments and strongly bind to actin filaments at a ratio of monomeric actin:GhKCH2-N = 1:0.6. The full length GhKCH2 recombinant protein was shown to bind to and cross-link microtubules and microfilaments in vitro. GFP fusion protein GFP-GhKCH2 transiently overexpressed in Arabidopsis protoplasts decorated both microtubules and microf... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2396665 Wed, 06 May 2009 04:00:00 +0100 2396665 http://www.medworm.com/index.php?rid=2184798&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20082117 We report here the first isolation of DRMs from purified plasma membranes of a tree species, the hybrid aspen Populus tremula x tremuloides, and their biochemical characterization. Plasma membranes were solubilised with Triton X-100 and the resulting DRMs were isolated by flotation in sucrose gradients. The DRMs were enriched in sterols, sphingolipids and glycosylphosphatidylinositol-anchored proteins and thus exhibited similar properties as DRMs from other species. However, they contained key carbohydrate synthases involved in cell wall polysaccharide biosynthesis, namely callose ((1→3)-β-D-glucan) and cellulose synthases. The association of these enzymes with DRMs was demonstrated using specific glucan synthase assays and antibodies, as well as biochemical and chemical appr... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2184798 Fri, 13 Feb 2009 05:00:00 +0100 2184798 http://www.medworm.com/index.php?rid=2170247&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20082315 A β-type carbonic anhydrase, PtCA1, of the marine diatom Phaeodactylum tricornutum was previously shown to occur in the chloroplast as clumped particles on the girdle lamellae. A series of deletions was carried out on the PtCA1 gene, ptca1, at regions encode N- or C-terminal domains of the mature PtCA1. These deletion constructs were fused with the enhanced-green-fluorescent-protein gene, egfp, introduced, and expressed in the cells of P. tricornutum. All three types of N-terminal deletions, ∆52-63, ∆64-75, and ∆76-87 relative to the initiation methionine showed little interference with the particle formation of the PtCA1::GFP fusion. Similarly, one of three types of C-terminal deletions, ∆253-262 was silent. However, the remaining two C-terminal deletion... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2170247 Mon, 09 Feb 2009 05:00:00 +0100 2170247 http://www.medworm.com/index.php?rid=2161324&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20080619 Pseudoalteromonas carageenovora κ-carrageenase is a glycoside hydrolase involved in the bioconversion of carrageenans. Carrageenans are sulphated galactans that are densely packed in red algal cell walls. Previous crystallographic investigations revealed that the active site of κ-carrageenase has a tunnel-shaped topology, suggesting a processive mode of action for this enzyme. To biochemically characterise the enzymatic depolymerisation of κ-carrageenan, soluble and solid substrates (in both gel and powder forms) were incubated with P. carageenovora κ-carrageenase. The average molecular weight of soluble carrageenan decreased rapidly and all possible degradation products were observed, suggesting random degradation of κ-carrageenan. In contrast, as expect... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2161324 Thu, 05 Feb 2009 05:00:00 +0100 2161324 http://www.medworm.com/index.php?rid=2062983&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20082195 Proteins that bind telomeric DNA modulate the structure of chromosome ends and control telomere function and maintenance. It has been shown that Arabidopsis thaliana AtTRB proteins from the single-myb-histone (SMH) family selectively bind double-stranded telomeric DNA and interact with the telomeric protein AtPOT1b, which is involved in telomere capping. Here we performed the first quantitative DNA binding study of this plant-specific family of proteins. Interactions of full-length proteins AtTRB1 and AtTRB3 with telomeric DNA were analyzed by electrophoretic mobility-shift assay, fluorescence anisotropy and surface plasmon resonance to reveal their binding stoichiometry and kinetics. Kinetic analyses at different salt conditions enabled us to estimate the electrostatic component of bindin... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2062983 Mon, 22 Dec 2008 05:00:00 +0100 2062983 http://www.medworm.com/index.php?rid=2056670&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20082004 CP12 is a small chloroplastic protein involved in the Calvin cycle that was shown to bind copper, a metal ion involved in modulation of its transition from reduced to oxidized state. In order to describe CP12 copper binding properties, copper-IMAC experiments and site-directed mutagenesis based on computational modeling, were coupled to top-down mass spectrometry (ESI-MS and MSMS). Copper-IMAC experiments allowed the primary characterization of mutation effects upon copper binding. Top-down MSMS experiments carried out under non-denaturing conditions on wild-type and mutant CP12/Cu2+ complexes then allowed fragment ions specifically liganding the copper ion to be determined. Comparison of MSMS datasets defined three regions involved in metal ion binding: residues D16 to D23, D38 to K50 and... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2056670 Mon, 22 Dec 2008 05:00:00 +0100 2056670 http://www.medworm.com/index.php?rid=2019049&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20081943 Arabidopsis thaliana COP10 is a ubiquitin-conjugating enzyme (E2) variant (UEV) which is required for repression of seedling photomorphogenesis in darkness. COP10 forms a complex (the CDD complex) with DET1 and DDB1a in vivo and can enhance the activity of ubiquitin-conjugating enzyme (E2) in vitro. To investigate whether COP10 might act as a general regulator of ubiquitin-conjugating enzymes, we tested the specificity of COP10 E2 enhancement activity across E2 families of Arabidopsis. We found that COP10 is capable of enhancing members from four E2 subgroups significantly, while having a milder effect on another. Surprisingly, we found that close canonical E2 homologs of COP10, such as UbcH5a, are also capable of enhancing E2s. Furthermore, we detected direct interactions between COP10 an... BJ Plant journals http://www.medworm.com/rss/comments.php?id=2019049 Fri, 05 Dec 2008 05:00:00 +0100 2019049 http://www.medworm.com/index.php?rid=1948373&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20081488 Mycobacterium brisbanense strain JK1, a bacterium capable of degrading the herbicide diuron, was isolated from herbicide exposed soil. A gene/enzyme system with diuron-hydrolase activity was isolated from this strain and named phenylurea hydrolase B (puhB/PuhB) because of its close similarity to the previously characterised phenylurea hydrolase A (puhA/PuhA). Both phenylurea hydrolases (PUHs) were heterologously expressed, purified and characterised. The PUHs were found to oligomerise as hexamers in solution, with each monomer containing a mononuclear Zn2+ active site. Sequence analysis shows that these enzymes belong to the metal-dependent amidohydrolase superfamily, although they contain a hitherto unreported Asn-x-His metal-binding motif and appear to form a novel sub-group within this ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1948373 Tue, 11 Nov 2008 05:00:00 +0100 1948373 http://www.medworm.com/index.php?rid=1931260&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20081256 Arabinoxylan arabinofuranohydrolases (AXH) are α-L-arabinofuranosidases that specifically hydrolyze the glycosidic bond between arabinofuranosyl substituents and xylopyranosyl backbone residues from arabinoxylan. Bacillus subtilis was recently shown to produce an AXH that cleaves arabinose units from O-2- or O-3-monosubstituted xylose residues: BsAXH-m2,3. Crystallographic analysis reveals a two domain structure for this enzyme: a catalytic domain displaying a 5-bladed β-propeller fold characteristic to glycoside hydrolase family (GH) 43 and a carbohydrate binding module (CBM) with a β-sandwich fold belonging to CBM family 6. Binding of substrate to BsAXH-m2,3 is largely based on hydrophobic stacking interactions which probably allow the positional flexibility needed t... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1931260 Tue, 04 Nov 2008 05:00:00 +0100 1931260 http://www.medworm.com/index.php?rid=1903285&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20081814 Internal compartmentalisation of metals is an important metal tolerance mechanism in many organisms. In plants and fungi, sequestration into the vacuole is a major detoxification mechanism for metals. Cation transport into the vacuole can be mediated by cation/H+ exchanger (CAX) transporters. The Arabidopsis thaliana AtCAX2 transporter was previously shown to transport Ca2+, Cd2+ and Mn2+. To assess the conservation of functional and regulatory characteristics of CAX2-like transporters in higher plants, we have characterized AtCAX2 orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2). Substrate specificity and regulatory activity was assessed using a yeast heterologous expression assay. Each CAX could transport Ca2+ and Mn2+ into the yeast vacuole but they each had di... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1903285 Fri, 24 Oct 2008 04:00:00 +0100 1903285 http://www.medworm.com/index.php?rid=1881277&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20081465 When a plant cell is challenged by a well-defined stimulus, complex signal transduction pathways are activated to promote the modulation of specific sets of genes and in fine to develop adaptive responses. In this context, protein phosphorylation plays a fundamental role through the activation of multiple protein kinase families. While the involvement of protein kinases at the plasma membrane and cytosolic levels are now well documented, their nuclear counterparts are still poorly investigated. In the field of plant defense reactions, no known study has yet reported the activation of a nuclear protein kinase and / or its nuclear activity in plant cells, although some protein kinases, e.g. MAPK, are known to be translocated into the nucleus. In the present report we investigated the ability... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1881277 Thu, 16 Oct 2008 04:00:00 +0100 1881277 http://www.medworm.com/index.php?rid=1776519&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20081151 In an effort to probe the structure and function of a predicted mitochondrial glyoxalase 2 (GLX2-1) from Arabidopsis thaliana, GLX2-1 was cloned, over-expressed, purified, and characterized using metal analyses, kinetics, and UV-Vis, EPR, and 1H NMR spectroscopies. The purified enzyme was purple and contained substoichiometric amounts of iron and zinc; however, metal binding studies reveal that GLX2-1 can bind nearly 2 equivalents of either iron or zinc and that the most stable analog of GLX2-1 is the iron-containing form. UV-Vis spectra of the purified enzyme suggest the presence of Fe(II) in the protein, but the Fe(II) can be oxidized over time or by the addition of metal ions to the protein. EPR spectra reveal the presence of an antiferromagnetically-coupled Fe(III)Fe(II) center and the... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1776519 Tue, 09 Sep 2008 04:00:00 +0100 1776519 http://www.medworm.com/index.php?rid=1740448&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20081146 In this study, we have examined in detail the only viable knockout mutant to date of one of these subunits in Arabidopsis thaliana, ClpR1. Loss of ClpR1 caused a slow-growth phenotype, with chlorotic leaves during early development that later partially recovered upon maturity. Analysis of the Clp proteolytic core in the clpR1 mutant (clpR1-1) revealed ca. 10% of the wild type levels remaining, likely due to a relative increase in the closely related ClpR3 protein and its partial substitution of ClpR1 in the core complex. A proteomic approach using an in organello proteolytic assay revealed 19 new potential substrates for the chloroplast Clp protease. Many of these substrates were constitutive enzymes involved in different metabolic pathways including photosynthetic carbon fixation, nitroge... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1740448 Fri, 29 Aug 2008 04:00:00 +0100 1740448 http://www.medworm.com/index.php?rid=1724392&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20081306 Plants exposed to hyperosmotic stress undergo changes in membrane dynamics and lipid composition to maintain cellular integrity and avoid membrane leakage. Various plant species respond to hyperosmotic stress with transient increases in phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2), however, the physiological role of such increases is unresolved. Here, the spatio-temporal dynamics of stress-induced changes in phosphoinositides (PIs) were analyzed in subcellular fractions of Arabidopsis leaves to delineate possible physiological roles. Unlabeled lipids were separated by thin-layer-chromatography and quantified according to gas-chromatographic detection of associated fatty acids. The plasma membrane represents the outermost barrier between the symplast of plant cells and its apoplast... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1724392 Fri, 22 Aug 2008 04:00:00 +0100 1724392 http://www.medworm.com/index.php?rid=1640559&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20080275 Water channel proteins (aquaporins) of the Plasma membrane Intrinsic Protein(PIP) subfamily provide means for fine and quick adjustments of the plant water status. A molecular model for gating of PIPs by cytosolic protons (H+) and divalent cations was derived from the atomic structure of spinach SoPIP2;1 in an open- and a closed-pore conformation. Here, we produced in Pichia pastoris the Arabidopsis AtPIP2;1 homolog, either wild-type (WT) or with mutations at residues supposedly involved in gating. Stopped-flow spectrophotometric measurements showed that, upon reconstitution in proteoliposomes, all forms function as water channels. First functional evidence for a direct gating of PIPs by divalent cations was obtained. In particular, cadmium and manganese were identified, in addition to cal... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1640559 Mon, 21 Jul 2008 04:00:00 +0100 1640559 http://www.medworm.com/index.php?rid=1635973&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20080568 Recent studies with the high-tillering mutants in Oryza sativa, the more axillary growth (max) mutants in Arabidopsis thaliana and the ramosus (rms) mutants in Pisum sativum have indicated the presence of a novel plant hormone that inhibits branching in an auxin-dependent manner. The synthesis of this inhibitor is initiated by the two carotenoid cleaving oxygenases (CCDs) OsCCD7/OsCCD8b, MAX3/MAX4 and RMS5/1 in rice, Arabidopsis and pea, respectively. MAX3 and MAX4 are thought to catalyze the successive cleavage of a carotenoid substrate yielding an apocarotenoid that, possibly after further modification, inhibits the outgrowth of axillary buds. To elucidate the substrate specificity of OsCCD8b, MAX4 and RMS1, we investigated their activities in vitro using naturally accumulated carotenoid... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1635973 Fri, 18 Jul 2008 04:00:00 +0100 1635973 http://www.medworm.com/index.php?rid=1599718&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20071555 Light signal transduction in plants involves an intricate series of pathways which is finely regulated by interactions between specific signaling proteins, as well as by protein modifications such as phosphorylation and ubiquitination. The identification of novel phytochrome-interacting proteins and the precise signaling mechanisms that they mediate is still ongoing. In our current study, we show that the newly identified putative phytochrome-associated protein, PAPP2C (phytochrome-associated protein phosphatase type 2C), interacts in the nucleus with phytochrome A (phyA) and B (phyB), both in vitro and in vivo. Moreover, the phosphatase activity of PAPP2C and its association with phytochromes were found to be enhanced by red light, indicating that it plays a role in mediating phytochrome ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1599718 Fri, 20 Jun 2008 04:00:00 +0100 1599718 http://www.medworm.com/index.php?rid=1599719&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20080668 The photosynthetic CO2-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) has long been a target for engineering kinetic improvements. Towards this goal we used a Rubisco dependent Escherichia coli (RDE) selection system to evolve Synechococcus PCC6301 Form I Rubisco under different selection pressures. In the fastest growing colonies the Rubisco large (L) subunit substitutions Ile-174-Val, Gln-212-Leu, Met-262-Thr, Phe-345-Leu or Phe-345-Ile were repeatedly selected and shown to increase functional Rubisco expression 4 to 7-fold in the RDE and 5 to 17-fold when expressed in XL1-Blue E. coli. Introducing the Phe-345-Ile L-subunit substitution into Synechococcus PCC7002 Rubisco improved its functional expression 11-fold in XL1-Blue cells but could not elicit functional ... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1599719 Mon, 19 May 2008 04:00:00 +0100 1599719 http://www.medworm.com/index.php?rid=1599720&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20080287 Hydrogen peroxide (H2O2) is a relatively long-lived reactive oxygen species that signals between cells and organisms. H2O2 signaling in plants is essential for response to stress, defense against pathogens, and the regulation of programmed cell death. Although H2O2 diffusion across membranes is often considered as a passive property of lipid bilayers, native membranes represent significant barriers for hydrogen peroxide. We addressed the question of whether channels might facilitate H2O2 transport across plasma membranes. The expression of several plant plasma membrane aquaporins in yeast, including PIP2;1 from Arabidopsis, enhanced the toxicity of H2O2 and increased the fluorescence of dye-loaded yeast when exposed to H2O2. The sensitivity of aquaporin-expressing yeast to hydrogen peroxid... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1599720 Thu, 08 May 2008 04:00:00 +0100 1599720 http://www.medworm.com/index.php?rid=1599721&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20080693 The protein NaGSL1 (Nicotiana alata glucan synthase-like 1) is implicated in the synthesis of callose, the 1,3-β-glucan that is the major polysaccharide in the walls of N. alata pollen tubes. Here we examine the production, intracellular location and post-translational processing of NaGSL1, and relate each of these to the regulation of pollen-tube callose synthase (CalS). The 220-kDa NaGSL1 polypeptide is produced after pollen-tube germination and accumulates during pollen-tube growth, as does CalS. A combination of membrane fractionation and immuno-electron microscopy revealed that NaGSL1 was present predominantly in ER and Golgi membranes in younger pollen tubes when CalS was mostly in an inactive (latent) form. In later stages of pollen-tube growth when CalS was present in both l... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1599721 Wed, 07 May 2008 04:00:00 +0100 1599721 http://www.medworm.com/index.php?rid=1599722&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20071641 The crystal structure of Arabidopsis thaliana peptide deformylase (AtPDF1B; EC 3.5.1.88), a plant specific deformylase, has been determined at a resolution of 2.4 Å. The overall fold of AtPDF1B is similar to other peptide deformylases that have been reported. Evidence from the crystal structure and gel filtration chromatography indicates that AtPDF1B exists as a symmetric dimer. PDF1B is essential in plants and has preferred substrate specificity towards the photosystem II D1 polypeptide. Comparative analysis of AtPDF1B, AtPDF1A, and the type 1B deformylase from Escherichia coli, identifies a number of differences in substrate binding subsites that might account for variations in sequence preference. A model of the N-terminal five amino acids from the D1 polypeptide bound in the act... BJ Plant journals http://www.medworm.com/rss/comments.php?id=1599722 Wed, 16 Apr 2008 04:00:00 +0100 1599722 http://www.medworm.com/index.php?rid=1599723&cid=s_37619_60_f&fid=37619&url=http%3A%2F%2Fwww.biochemj.org%2Fbj%2Fimps%2Frefer.htm%3FMSID%3DBJ20071568 In conclusion, both typical and atypical Arabidopsis U-box proteins were active E3s. The overlap in the E3/E2 selectivity suggests that in vivo specificity is not determined only by the E3/E2 interactions but also by other parameters, e.g. co-existence or interactions with additional domains. The biochemical functions of AtPUB49 suggest that the protein can be involved in folding or degradation of protein substrates. Similar functions can also be retained within a protein complex with separate chaperone and U-box proteins. (Source: BJ Plant) BJ Plant journals http://www.medworm.com/rss/comments.php?id=1599723 Mon, 07 Apr 2008 04:00:00 +0100 1599723