Identification of bypass reactions leading to the formation of one central steroid degradation intermediate in metabolism of different bile salts in Pseudomonas sp strain Chol1
Identification of bypass reactions leading to the formation of one central steroid degradation intermediate in metabolism of different bile salts in Pseudomonas sp strain Chol1
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DOI：
10.1111/1462-2920.13192
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发表时间：
2016-10-01
影响因子：
5.1
通讯作者：
Philipp, Bodo
中科院分区：
文献类型：
--
作者：
Holert, Johannes;Yuecel, Onur;Philipp, Bodo
胆汁盐胆酸盐、脱氧胆酸盐、鹅脱氧胆酸盐和石胆酸盐从脊椎动物释放到土壤和水中，在那里环境细菌降解这些广泛分布的类固醇化合物。研究了在模式生物假单胞菌属菌株Chol 1中降解这些三羟基化、二羟基化和单羟基化胆汁盐是否需要不同的酶。可用的和新的突变体的实验表明，C-5-羧基侧链连接到类固醇骨架的降解是由相同的一套酶催化。发现部分降解的胆汁盐（由H-甲基六氢茚酮丙酸酯（HIP）组成）的降解存在差异。对于在类固醇骨架的C7处缺乏羟基的脱氧胆酸盐和石胆酸盐，需要额外的酰基-辅酶A（CoA）脱氢酶用于连接至甲基六氢茚酮部分的C-3-羧基侧链的β-氧化。该侧链的b-氧化可以在体外测量。与胆酸盐和脱氧胆酸盐，还原脱羟基的HIP的C12-羟基基团是必需的。该反应步骤的候选基因的缺失揭示了迄今未知的类固醇脱氢酶和类固醇氧化还原酶负责该CoA依赖性反应。这些结果表明，所有胆汁盐通过旁路反应被引导至共同途径，其中3 '-羟基-HIP-CoA作为中心中间体。
The bile salts cholate, deoxycholate, chenodeoxycholate and lithocholate are released from vertebrates into soil and water where environmental bacteria degrade these widespread steroid compounds. It was investigated whether different enzymes are required for the degradation of these tri-, di- and monohydroxylated bile salts in the model organism Pseudomonas sp. strain Chol1. Experiments with available and novel mutants showed that the degradation of the C-5-carboxylic side chain attached to the steroid skeleton is catalysed by the same set of enzymes. A difference was found for the degradation of partially degraded bile salts consisting of H-methylhexahydroindanone-propanoates (HIPs). With deoxycholate and lithocholate, which lack a hydroxy group at C7 of the steroid skeleton, an additional acyl-coenzyme A (CoA) dehydrogenase was required for beta-oxidation of the C-3-carboxylic side chain attached to the methylhexahydroindanone moiety. The b-oxidation of this side chain could be measured in vitro. With cholate and deoxycholate, a reductive dehydroxylation of the C12-hydroxy group of HIP was required. Deletion of candidate genes for this reaction step revealed that a so-far unknown steroid dehydratase and a steroid oxidoreductase were responsible for this CoA-dependent reaction. These results showed that all bile salts are channelled into a common pathway via bypass reactions with 3'-hydroxy-HIP-CoA as central intermediate.