Biosynthesis of the Myxobacterial Antibiotic Corallopyronin A

Corallopyronin A is a myxobacterial compound with potent antibacterial activity. Feeding experiments with labelled precursors resulted in the deduction of all biosynthetic building blocks for corallopyronin A and revealed an unusual feature of this metabolite: its biosynthesis from two chains, one solely PKS‐derived and the other NRPS/PKS‐derived. The starter molecule is believed to be carbonic acid or its monomethyl ester. The putative corallopyronin A biosynthetic gene cluster is a trans‐AT‐type mixed PKS/NRPS gene cluster, containing a β‐branching cassette. Striking features of this gene cluster are a NRPS‐like adenylation domain that is part of a PKS‐type module and is believed to be responsible for glycine incorporation, as well as split modules with individual domains occurring on different genes. It is suggested that CorB is a trans‐acting ketosynthase and it is proposed that it catalyses the Claisen condensation responsible for the interconnection of the two chains. Additionally, the stereochemistry of corallopyronin A was deduced by a combination of a modified Mosher's method and ozonolysis with subsequent chiral GC analyses.     

Synthetic Chain Terminators Off‐Load Intermediates from a Type I Polyketide Synthase

Modular biocatalysis is responsible for the generation of countless bioactive products and its mining remains a major focus for drug discovery purposes. One of the enduring hurdles is the isolation of biosynthetic intermediates in a readily‐analysed form. We prepared a series of nonhydrolysable pantetheine and N‐acetyl cysteamine mimics of the natural (methyl)malonyl extender units recruited for polyketide formation. Using these analogues as competitive substrates, we were able to trap and off‐load diketide and triketide species directly from an in vitro reconstituted type I polyketide synthase, the 6‐deoxyerythronolide B synthase 3 (DEBS3). The putative intermediates, which were extracted in organic solvent and characterised by LC‐HR‐ESI‐MS, are the first of their kind and prove that small‐molecule chain terminators can be used as convenient probes of the biosynthetic process.     

利用椰子水生物合成CMC改性细菌纤维素

以椰子水为培养基,于培养基中添加羧甲基纤维素(CMC)后培养木醋杆菌可制备羧甲基纤维素改性细菌纤维素(CMC-BC)。当添加6g/LCMC时,CMC-BC产量达到最大(10.41g/L),是纯BC产量(4.73g/L)的2.2倍。采用FTIR表征了产物结构;通过SEM、XRD、TGA研究了产物性能;并测试了产物的特性黏度与含水率。结果显示,利用椰子水所制备的CMC-BC缩短了培养时间(3d)。适量添加CMC〔ρ(CMC)=2～18g/L〕时,CMC-BC的聚合度增大,且具有较好热稳定性及较高含水率。CMC-BC还表现出较好的溶解性能。     

Understanding different regulatory mechanisms of proteinaceous and non-proteinaceous amino acid formation in tea (Camellia sinensis) provides new insights into the safe and effective alteration of tea flavor and function

Abstract

Amino acids are the main contributors to tea (Camellia sinensis) flavor and function. Tea leaves contain not only proteinaceous amino acids but also specialized non-proteinaceous amino acids such as L-theanine and γ-aminobutyric acid (GABA). Here, we review different regulatory mechanisms of proteinaceous and non-proteinaceous amino acid formation in tea. The key findings were: (1) High accumulations of proteinaceous amino acids mainly result from protein degradation, which occurs in each tea stage, including preharvest, postharvest, manufacturing, and deep processing; (2) L-Theanine is the most represented non-proteinaceous amino acid that contributes to tea taste and function. Its accumulation is influenced more by the variety than by exogenous factors; and (3) GABA is the second most represented non-proteinaceous amino acid that contributes to tea function. Its formation, and resulting accumulation, are responses to stress. The combination of anoxic stress and mechanical damage are essential for a high GABA accumulation. An understanding of the biosynthesis, metabolism, and regulatory mechanisms of the proteinaceous and non-proteinaceous amino acids during the whole process from raw materials to tea products is necessary to safely and effectively alter tea flavor and function.     

前体物质对辅酶Q_(10)生物合成的影响

首次研究了以辅酶Q10 (CoQ10 )主要侧链供给前体物质———茄尼醇和醌环供给前体———羟基苯甲酸和辅酶Q0 对粟酒裂殖酵母(Schizosaccharomycespromb 2 1794 - 2 3) 生产CoQ10 产量的影响,并对前体的转化工艺进行了初步研究。确定了适宜于粟酒裂殖酵母生长及高转化前体生成CoQ10 的条件为:酵母在2 8℃下,2 2 0r/min于发酵培养基中培养18h后,加入0 5 g/L茄尼醇继续发酵培养18h ,进行前体转化反应。结果表明,单独添加茄尼醇能达到最大产量33 1mg/L ,比对照样品增加了91% ,任2种前体物质共同添加都要比单独添加茄尼醇时产量低。茄尼醇和CoQ0 共同添加时,单位细胞胞外辅酶CoQ10 的产量达到最高的1 35mg/g ,比对照样品增加了117%。     

纳米纤维的技术进展

本文简单介绍了纳米纤维的定义、特点和应用 ,主要讨论了纳米纤维的制备方法 ,包括传统纺丝方法(如 :静电纺丝法、复合纺丝法和分子喷丝板法 )的改进以及新兴的生物合成法和化学合成法     

促进剂对辅酶Q10生物合成的影响

目的研究不同的添加物对辅酶Q10发酵合成的影响。方法辅酶Q10用皂化法提取,高效液相法检测。结果添加与辅酶Q10的合成有关物质如对羟基苯甲酸、胡萝卜汁、西红柿汁及烟叶,均能提高辅酶Q10的产量,分别提高6.3%、9.0%、18.1%、12.1%。     

Studies on the Biosynthesis of the Stephacidin and Notoamide Natural Products: A Stereochemical and Genetic Conundrum

The stephacidin and notoamide natural products belong to a group of prenylated indole alkaloids containing a bicyclo[2.2.2]diazaoctane core. Biosynthetically, this bicyclic core is believed to be the product of an intermolecular Diels–Alder (IMDA) cycloaddition of an achiral azadiene. Since all of the natural products in this family have been isolated in enantiomerically pure form to date, it is believed that an elusive Diels–Alderase enzyme mediates the IMDA reaction. Adding further intrigue to this biosynthetic puzzle is the fact that several related Aspergillus fungi produce a number of metabolites with the opposite absolute configuration, implying that these fungi have evolved enantiomerically distinct Diels–Alderases. We have undertaken a program to identify every step in the biogenesis of the stephacidins and notoamides, and by combining the techniques of chemical synthesis and biochemical analysis we have been able to identify the two prenyltransferases involved in the early stages of the stephacidin and notoamide biosyntheses. This has allowed us to propose a modified biosynthesis for stephacidin A, and has brought us closer to our goal of finding evidence for, or against, the presence of a Diels–Alderase in this biosynthetic pathway.