Clostridium scindens baiCD and baiH genes encode stereo-specific 7α/7β-hydroxy-3-oxo-Δ4-cholenoic acid oxidoreductases
Clostridium scindens baiCD and baiH genes encode stereo-specific 7α/7β-hydroxy-3-oxo-Δ4-cholenoic acid oxidoreductases
复制标题
DOI：
10.1016/j.bbalip.2007.10.008
复制
发表时间：
2008-01-01
影响因子：
4.8
通讯作者：
Hylemon, Phillip B.
中科院分区：
文献类型：
--
作者：
Kang, Dae-Joong;Ridlon, Jason M.;Hylemon, Phillip B.
由肠道细菌形成的次级胆汁酸被认为在人类胃肠道癌症中起重要作用。胆汁酸7 α/β-脱羟基作用是由几种肠道梭菌进行的，这些梭菌具有多基因胆汁酸诱导（bai）操纵子。已经克隆和表征了在该途径中编码酶的几个基因。然而，尚未将基因产物分配给胆酸（CA）、鹅去氧胆酸（CDCA）或熊去氧胆酸（UDCA）的3-氧代-δ（4）-胆烯酸中间体的产生。我们以前报道，baiH基因编码的NADH：黄素氧化还原酶（NADH：FOR），然而，这种蛋白质在胆汁酸7-脱羟基化的作用还不清楚。同源性搜索和二级结构比对表明，这种蛋白质类似于黄素蛋白，减少α/β-不饱和羰基化合物。baiH基因产物在大肠杆菌中表达，纯化并发现是立体特异性NAD（H）依赖性7 β-羟基-3-氧代-δ（4）-胆烯酸氧化还原酶。此外，baiH和baiCD基因产物之间的高序列相似性表明baiCD基因可能编码对CDCA和CA特异性的3-氧代-δ（4）-胆烯酸氧化还原酶。我们使用从过表达baiCD基因的大肠杆菌制备的细胞提取物测试了这一假设，并发现它编码立体特异性NAD（H）依赖性7 α-羟基-3-氧代-δ（4）-胆烯酸氧化还原酶。(c)2007 Elsevier B.V保留所有权利。
Secondary bile acids, formed by intestinal bacteria, are suggested to play a significant role in cancers of the gastrointestinal tract in humans. Bile acid 7 alpha/beta-dehydroxylation is carried out by a few species of intestinal clostridia which harbor a multi-gene bile acid inducible (bai) operon. Several genes encoding enzymes in this pathway have been cloned and characterized. However, no gene product(s) has yet been assigned to the production of 3-oxo-Delta(4) -cholenoic acid intermediates of cholic acid (CA), chenodeoxycholic acid (CDCA) or ursodeoxycholic acid (UDCA). We previously reported that the baiH gene encodes an NADH:flavin oxidoreductase (NADH:FOR); however, the role of this protein in bile acid 7-dehydroxylation is unclear. Homology searches and secondary structural alignments suggest this protein to be similar to flavoproteins which reduce alpha/beta-unsaturated carbonyl compounds. The baiH gene product was expressed in Escherichia coli, purified and discovered to be a stereo-specific NAD(H)-dependent 7 beta-hydroxy-3-oxo-Delta(4) -cholenoic acid oxidoreductase. Additionally, high sequence similarity between the baiH and baiCD gene products suggests the baiCD gene may encode a 3-oxo-Delta(4)-cholenoic acid oxidoreductase specific for CDCA and CA. We tested this hypothesis using cell extracts prepared from E coli overexpressing the baiCD gene and discovered that it encodes a stereo-specific NAD(H)-dependent 7 alpha-hydroxy-3-oxo-Delta(4)- cholenoic acid oxidoreductase. (c) 2007 Elsevier B.V All rights reserved.