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首页> 外文期刊>Journal of bacteriology >The Essential Function of Genes for a Hydratase and an Aldehyde Dehydrogenase for Growth of Pseudomonas sp. Strain Chol1 with the Steroid Compound Cholate Indicates an Aldolytic Reaction Step for Deacetylation of the Side Chain
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The Essential Function of Genes for a Hydratase and an Aldehyde Dehydrogenase for Growth of Pseudomonas sp. Strain Chol1 with the Steroid Compound Cholate Indicates an Aldolytic Reaction Step for Deacetylation of the Side Chain

机译：水合酶和醛脱氢酶的基因对于假单胞菌属sp的生长的基本功能。带有类固醇化合物胆酸盐的菌株Chol1表示侧链脱乙酰化的Aldolytic反应步骤

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In the bacterial degradation of steroid compounds, the enzymes initiating the breakdown of the steroid rings are well known, while the reactions for degrading steroid side chains attached to C-17 are largely unknown. A recent in vitro analysis with Pseudomonas sp. strain Chol1 has shown that the degradation of the C5 acyl side chain of the C24 steroid compound cholate involves the C22 intermediate 7α,12α-dihydroxy-3-oxopregna-1,4-diene-20S-carbaldehyde (DHOPDCA) with a terminal aldehyde group. In the present study, candidate genes with plausible functions in the formation and degradation of this aldehyde were identified. All deletion mutants were defective in growth with cholate but could transform it into dead-end metabolites. A mutant with a deletion of the shy gene, encoding a putative enoyl coenzyme A (CoA) hydratase, accumulated the C24 steroid (22E)-7α,12α-dihydroxy-3-oxochola-1,4,22-triene-24-oate (DHOCTO). Deletion of the sal gene, formerly annotated as the steroid ketothiolase gene skt, resulted in the accumulation of 7α,12α,22-trihydroxy-3-oxochola-1,4-diene-24-oate (THOCDO). In cell extracts of strain Chol1, THOCDO was converted into DHOPDCA in a coenzyme A- and ATP-dependent reaction. A sad deletion mutant accumulated DHOPDCA, and expression in Escherichia coli revealed that sad encodes an aldehyde dehydrogenase for oxidizing DHOPDCA to the corresponding acid 7α,12α-dihydroxy-3-oxopregna-1,4-diene-20-carboxylate (DHOPDC) with NAD+ as the electron acceptor. These results clearly show that the degradation of the acyl side chain of cholate proceeds via an aldolytic cleavage of an acetyl residue; they exclude a thiolytic cleavage for this reaction step. Based on these results and on sequence alignments with predicted aldolases from other bacteria, we conclude that the enzyme encoded by sal catalyzes this aldolytic cleavage.
机译：在类固醇化合物的细菌降解中，引发类固醇环分解的酶是众所周知的，而降解连接至C-17的类固醇侧链的反应是未知的。最近使用假单胞菌（Pseudomonas sp。）进行的体外分析。 Chol1菌株显示C 24 类固醇化合物胆酸盐的C 5 酰基侧链的降解涉及C 22 中间体7α，12α -带有末端醛基的-二羟基-3-氧代opregna-1，4-二烯-20 S -甲醛（DHOPDCA）。在本研究中，鉴定了在该醛的形成和降解中具有合理功能的候选基因。所有的缺失突变体在胆酸盐的生长上都是有缺陷的，但是可以将其转化为末端代谢产物。编码假定推定的烯酰辅酶A（CoA）水合酶的 shy 基因缺失的突变体，积累了C 24 类固醇（22 E ）-7α，12α-二羟基-3-氧杂ola-1,4,22-三烯-24-酸酯（DHOCTO）。先前被称为类固醇酮硫解酶基因 skt 的 sal 基因的缺失导致7α，12α，22-trihydroxy-3-oxochola-1,4-的积累二烯24酸酯（THOCDO）。在菌株Chol1的细胞提取物中，THOCDO在辅酶A和ATP依赖性反应中转化为DHOPDCA。一个 sad 缺失突变体积累了DHOPDCA，在大肠杆菌中的表达表明 sad 编码了一种醛脱氢酶，用于将DHOPDCA氧化为相应的酸7α，12α-dihydroxy-3-oxopregna-以NAD + 为电子受体的1,4-二烯-20-羧酸盐（DHOPDC）。这些结果清楚地表明，胆酸盐的酰基侧链的降解通过乙酰基残基的醛基裂解而进行。它们排除了该反应步骤中的硫解裂解。根据这些结果以及与其他细菌预测的醛缩酶的序列比对，我们得出结论， sal 编码的酶催化这种醛解酶切。

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