Crystal structure of beta-ketoacyl-acyl carrier protein synthase II from E.coli reveals the molecular architecture of condensing enzymes.

In the biosynthesis of fatty acids, the beta-ketoacyl-acyl carrier protein (ACP) synthases catalyze chain elongation by the addition of two-carbon units derived from malonyl-ACP to an acyl group bound to either ACP or CoA. The crystal structure of beta-ketoacyl synthase II from Escherichia coli has been determined with the multiple isomorphous replacement method and refined at 2.4 A resolution. The subunit consists of two mixed five-stranded beta-sheets surrounded by alpha-helices. The two sheets are packed against each other in such a way that the fold can be described as consisting of five layers, alpha-beta-alpha-beta-alpha. The enzyme is a homodimer, and the subunits are related by a crystallographic 2-fold axis. The two active sites are located near the dimer interface but are approximately 25 A apart. The proposed nucleophile in the reaction, Cys163, is located at the bottom of a mainly hydrophobic pocket which is also lined with several conserved polar residues. In spite of very low overall sequence homology, the structure of beta-ketoacyl synthase is similar to that of thiolase, an enzyme involved in the beta-oxidation pathway, indicating that both enzymes might have a common ancestor.     

SMAD4 contributes to chondrocyte and osteocyte development

Different cellular and molecular mechanisms contribute to chondrocyte and osteocyte development. Although vital roles of the mothers against decapentaplegic homolog 4 (also called ‘SMAD4’) have been discussed in different cancers and stem cell‐related studies, there are a few reviews summarizing the roles of this protein in the skeletal development and bone homeostasis. In order to fill this gap, we discuss the critical roles of SMAD4 in the skeletal development. To this end, we review the different signalling pathways and also how SMAD4 defines stem cell features. We also elaborate how the epigenetic factors—ie DNA methylation, histone modifications and noncoding RNAs—make a contribution to the chondrocyte and osteocyte development. To better grasp the important roles of SMAD4 in the cartilage and bone development, we also review the genotype‐phenotype correlation in animal models. This review helps us to understand the importance of the SMAD4 in the chondrocyte and bone development and the potential applications for therapeutic goals.     

The distribution of caprylate, caprate and laurate in lipids from developing and mature seeds of transgenic Brassica napus L.

The composition and positional distribution of lipids in developing and mature transgenic Brassica napus seeds accumulating up to 7 mol% of caprylate (8:0), 29 mol% caprate (10:0) or 63 mol% of laurate (12:0) were examined. The accumulation of 8:0 and 10:0 resulted from over-expression of the medium-chain-specific thioesterase (Ch FatB2) alone or together with the respective chain-length-specific condensing enzyme (Ch KASIV). Seeds containing high levels of 12:0 were obtained from plants expressing bay thioesterase (BTE) alone or crossed with a line over-expressing the coconut lysophosphatidic acid acyltransferase (LPAAT), an enzyme responsible for the increase in acylation of 12:0 at the sn-2 position. In all instances, 10:0 and 12:0 fatty acids were present in substantial amounts in phosphatidylcholine during seed development with a drastic decrease of 80–90% in mature seeds. At all stages of seed development however, 8:0 was barely detectable in this membrane lipid. Altogether, these results indicate that these transgenic seeds exclude and/or remove the medium-chain fatty acids from their membrane and that this mechanism(s) is more effective with the shorter-chain fatty acids. Furthermore, seeds of 8:0- and 10:0-producing lines had only negligible levels of these fatty acids present in the sn-2 position of the triacylglycerols. In contrast, all 12:0-producing seeds had a substantial amount of this fatty acid in the sn-2 position of the triacylglycerols, suggesting that the endogenous LPAAT is able to acylate 12:0 if no other acyl-CoA species are available. Received: 11 February 2000 / Accepted: 2 May 2000     

伊朗Karaj地区双孢蘑菇上的螨类调查（英文）

2004年春季至2006年夏季期间,调查了伊朗Karaj地区双孢蘑菇上的螨类,发现了3目9科17种食菌性、捕食性和腐食性螨类,包括：光滑巨螯螨Macrocheles glaber (Müller),粪巨螯螨Macrocheles merdarius (Berlese),近褐巨螯螨Macrocheles subbadius(Berlese),甲虫寄螨Parasitus coleoptratorum （Linnaeus）,粪堆寄螨Parasitus fimetorum （Berlese）,乳突寄螨Parasitus mammillatus (Berlese),Sancassania rodionovi Zachvatkin,腐食酪螨Tyrophagus putrescentiae (Schrank),Uroobovella fimicola (Berlese),Ameroseius fungicolus^* Masan,Pediculaster kneeboni^* Wicht,Pediculaster flechtmanni^* Wicht,Scutacarus longitarsus (Berlese),Dendrolaelaps multidentatus^* Masan,柴特北绥螨Arctoseius cetratus (Sellnick),Lasioseius sugawarai^* Ehara和Ameroseius plumigera Oudemans。其中有“*”号标记的6个种为伊朗新纪录种,12个种为在蘑菇上首次发现。     

The NADPH-protochlorophyllide oxidoreductase is the major protein constituent of prolamellar bodies in wheat (Triticum aestivum L.)

A fraction of highly purified prolamellar bodies was isolated from etioplasts of wheat (Triticum aestivum L. cv. Starke II, Weibull), as previously described by Ryberg and Sundqvist (1982, Physiol. Plant., 56, 125–132). Studies on the protein composition revealed that only one major polypeptide of an apparent molecular weight of 36000 is present in the fraction of prolamellar bodies. This polypeptide was identified as the NADPH-protochlorophyllide oxidoreductase. The highest specific activity of the enzyme in etiolated leaf tissue was confirmed to be in the fraction of prolamellar bodies.Abbreviations PChlide protochlorophyllide - PLB prolamellar body - PT prothylakoid     

GT-2: a transcription factor with twin autonomous DNA-binding domains of closely related but different target sequence specificity.

A triplet of adjacent, highly similar GT motifs in the phyA promoter of rice functions to support maximal expression of this gene. We have obtained a recombinant clone that encodes a full-length nuclear protein, designated GT-2, which binds specifically to these target sequences. This novel protein contains acidic, basic and proline- + glutamine-rich regions, as well as two autonomous DNA-binding domains, one NH2-terminal and the other COOH-terminal, that discriminate with high resolution between the three GT motifs. A duplicated sequence of 75 amino acids, present once in each DNA-binding domain, appears likely to mediate DNA target element recognition. Each copy of this duplicated protein sequence is predicted to form three amphipathic alpha-helices separated from each other by two short loops. The absence of sequence similarity to other known proteins suggests that this predicted structural unit, which we term the trihelix motif, might be representative of a new class of DNA-binding proteins.     

Chlorophyll synthesis in green leaves and isolated chloroplasts of barley (Hordeum vulgare)

The photoreduction of protochlorophyllide was studied in leaves and isolated chloroplasts of barley. Leaves of plants which had been preilluminated for varying lengths of time were incubated with [¹⁴C]-δ- aminolevulinic acid for 2 h in the dark. The subsequent photoreduction of [¹⁴C]-protochlorophyllide was analyzed by high performance liquid chromatography of pigments extracted from illuminated leaves and plastids. The plastids used in this study were isolated in the dark from leaves at the end of the 2 h labelling period. Three major results were obtained:

• 1

  The extent of protochlorophyllide reduction in vivo was rapidly reduced as a function of the preillumination period. In 24 h preilluminated plants only a small fraction of the radioactively labelled protochlorophyllide was reduced during the subsequent light period.
• 2

  The amount of NADPH-protochlorophyllide oxidoreductase (EC 1.6.99.-) present in plastids of fully-green plants was drastically reduced relative to levels in plastids of dark-grown plants as estimated by the methods of immunoblotting of plastid proteins and immunogold labelling of ultrathin sections of the leaf tissue.
• 3

  In etiolated plants light seemed to affect the reduction of protochlorophyllide directly through the excitation of protochlorophyllide. In fully green plants, however, light also affected chlorophyll formation indirectly by the supply of NADPH via photosynthetic electron transport.