代谢
乙醇胺可以被多种系统发育不同的细菌用作碳和氮的来源。乙醇胺-氨裂合酶是分解乙醇胺为乙醛和氨的酶,由串联基因eutBC编码。尽管对肠炎沙门氏菌鼠伤寒血清型对乙醇胺利用进行了广泛的研究,但对于EutBC的结构和催化机制、乙醇胺利用的进化起源,以及乙醇胺本身与乙醇胺-氨裂合酶辅因子腺苷钴胺素之间的调控联系,还有很多需要了解。我们通过对乙醇胺-氨裂合酶的序列、结构、基因组环境和系统发育的计算分析来回答这些问题,并评估了近期提出细菌食物中毒与二醇利用途径相关性的数据挖掘研究。我们发现EutBC的进化包括招募一个TIM桶结构域和一个Rossmann折叠结构域,并将它们分别与N末端的α-螺旋结构域融合,形成了EutB和EutC。这种融合之后,在厚壁菌门中招募并偶尔丢失辅助乙醇胺利用基因,并通过几次水平转移,尤其是从厚壁菌门干细胞到肠杆菌科,以及从α-变形菌门到放线菌门。我们鉴定了一个可能代表EutR结合位点的保守DNA基序,这个基序在几种肠杆菌科的乙醇胺和钴胺素操纵子中共享,这表明这些物种中存在一种将无酶蛋白和辅因子生物合成联系起来的机制。最后,我们发现食物中毒表型与代谢体的结构成分的联系比与乙醇胺利用基因或与其同源的丙二醇利用基因本身更为紧密。
Ethanolamine can be used as a source of carbon and nitrogen by phylogenetically diverse bacteria. Ethanolamine-ammonia lyase, the enzyme that breaks ethanolamine into acetaldehyde and ammonia, is encoded by the gene tandem eutBC. Despite extensive studies of ethanolamine utilization in Salmonella enterica serovar Typhimurium, much remains to be learned about EutBC structure and catalytic mechanism, about the evolutionary origin of ethanolamine utilization, and about regulatory links between the metabolism of ethanolamine itself and the ethanolamine-ammonia lyase cofactor adenosylcobalamin. We used computational analysis of sequences, structures, genome contexts, and phylogenies of ethanolamine-ammonia lyases to address these questions and to evaluate recent data-mining studies that have suggested an association between bacterial food poisoning and the diol utilization pathways. We found that EutBC evolution included recruitment of a TIM barrel and a Rossmann fold domain and their fusion to N-terminal alpha-helical domains to give EutB and EutC, respectively. This fusion was followed by recruitment and occasional loss of auxiliary ethanolamine utilization genes in Firmicutes and by several horizontal transfers, most notably from the firmicute stem to the Enterobacteriaceae and from Alphaproteobacteria to Actinobacteria. We identified a conserved DNA motif that likely represents the EutR-binding site and is shared by the ethanolamine and cobalamin operons in several enterobacterial species, suggesting a mechanism for coupling the biosyntheses of apoenzyme and cofactor in these species. Finally, we found that the food poisoning phenotype is associated with the structural components of metabolosome more strongly than with ethanolamine utilization genes or with paralogous propanediol utilization genes per se.
来源:Hazardous Substances Data Bank (HSDB)