Mallonee D H, Adams J L, Hylemon P B
Department of Microbiology and Immunology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298-0678.
J Bacteriol. 1992 Apr;174(7):2065-71. doi: 10.1128/jb.174.7.2065-2071.1992.
The baiB gene from Eubacterium sp. strain VPI 12708 was previously cloned, sequenced, and shown to be part of a large bile acid-inducible operon encoding polypeptides believed to be involved in bile acid 7 alpha-dehydroxylation. In the present study, the baiB gene was subcloned and expressed in Escherichia coli and shown to encode a bile acid-coenzyme A (CoA) ligase. This ligase required a C-24 bile acid with a free carboxyl group, ATP, Mg2+, and CoA for synthesis of the final bile acid-CoA conjugate. Product analysis by reverse-phase high-performance liquid chromatography revealed final reaction products that comigrated with cholyl-CoA and AMP. A putative bile acid-AMP intermediate was detected when CoA was omitted from the reaction mixture. The bile acid-CoA ligase has amino acid sequence similarity to several other polypeptides involved in the ATP-dependent linking of AMP or CoA to cyclic carboxylated compounds. The bile acid-CoA ligation is believed to be the initial step in the bile acid 7 alpha-dehydroxylation pathway in Eubacterium sp. strain VPI 12708.
来自真杆菌属菌株VPI 12708的baiB基因先前已被克隆、测序，并被证明是一个大型胆汁酸诱导型操纵子的一部分，该操纵子编码的多肽被认为参与胆汁酸7α-脱羟基作用。在本研究中，baiB基因被亚克隆并在大肠杆菌中表达，结果表明它编码一种胆汁酸辅酶A（CoA）连接酶。这种连接酶合成最终的胆汁酸-CoA结合物需要一个具有游离羧基的C-24胆汁酸、ATP、Mg2+和CoA。通过反相高效液相色谱进行的产物分析显示，最终反应产物与胆酰辅酶A和AMP同时迁移。当反应混合物中省略CoA时，检测到一种假定的胆汁酸-AMP中间体。该胆汁酸-CoA连接酶与其他几种参与将AMP或CoA与环状羧化化合物进行ATP依赖性连接的多肽具有氨基酸序列相似性。胆汁酸-CoA连接被认为是真杆菌属菌株VPI 12708中胆汁酸7α-脱羟基途径的起始步骤。
