Anaerobic Metabolism of Indoleacetate
Anaerobic Metabolism of Indoleacetate
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DOI：
10.1128/jb.00250-12
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发表时间：
2012-06-01
影响因子：
3.2
通讯作者：
Fuchs, Georg
中科院分区：
文献类型：
--
作者：
Ebenau-Jehle, Christa;Thomas, Markus;Fuchs, Georg
研究了吲哚乙酸（吲哚-3-乙酸[IAA]）在产酶β-变形杆菌Azoarcus evansii中的厌氧代谢。该菌株能完全氧化IAA，生长周期为10 h。转化IAA的酶活性存在于IAA生长的细胞的可溶性细胞部分中，但在2-氨基苯甲酸盐或苯甲酸盐生长的细胞中下调10倍。IAA的转化不需要分子氧，但需要电子受体如NAD（+）或人工染料。第一个被鉴定的产物是2-氧代-IAA的烯醇和酮形式。后来，观察到了极性产物，但尚不能确定。第一步可能包括N-杂环吡咯环厌氧羟基化为烯醇形式的2-氧代-IAA，其由含钼辅因子的脱氢酶催化。这一步骤之后可能是水解开环的酮形式，这是催化的乙内酰脲酶样酶。IAA和苯甲酸盐生长的细胞的蛋白质组的比较确定IAA诱导的蛋白质。由于A. evansii与基因组已知的EbN 1菌株的杂交，我们鉴定了一组编码IAA诱导蛋白的14个基因，这些蛋白参与IAA代谢的早期步骤。这些基因包括黄嘌呤氧化酶/醛脱氢酶家族的钼辅因子依赖性脱氢酶、乙内酰脲酶、辅酶A（CoA）连接酶、CoA转移酶、辅酶B-12依赖性脱氢酶、酰基-CoA脱氢酶、烯酰-CoA水合酶和3-羟酰基-CoA脱氢酶的融合蛋白、β-酮硫解酶、和用于ABC转运的周质底物结合蛋白以及GntR家族的转录调节因子。五种预测的酶形成或作用于CoA硫酯，表明在IAA的初始氧化和可能的开环后不久，CoA硫酯形成，碳骨架重排，随后是另一种CoA硫酯的CoA依赖性硫解释放。我们提出了一个厌氧IAA代谢途径，最终导致2-氨基苯甲酰辅酶A或苯甲酰辅酶A的计划。
The anaerobic metabolism of indoleacetate (indole-3-acetic acid [IAA]) in the denitrifying betaproteobacterium Azoarcus evansii was studied. The strain oxidized IAA completely and grew with a generation time of 10 h. Enzyme activities that transformed IAA were present in the soluble cell fraction of IAA-grown cells but were 10-fold downregulated in cells grown on 2-aminobenzoate or benzoate. The transformation of IAA did not require molecular oxygen but required electron acceptors like NAD(+) or artificial dyes. The first products identified were the enol and keto forms of 2-oxo-IAA. Later, polar products were observed, which could not yet be identified. The first steps likely consist of the anaerobic hydroxylation of the N-heterocyclic pyrrole ring to the enol form of 2-oxo-IAA, which is catalyzed by a molybdenum cofactor-containing dehydrogenase. This step is probably followed by the hydrolytic ring opening of the keto form, which is catalyzed by a hydantoinase-like enzyme. A comparison of the proteome of IAA- and benzoate-grown cells identified IAA-induced proteins. Owing to the high similarity of A. evansii with Strain EbN1, whose genome is known, we identified a cluster of 14 genes that code for IAA-induced proteins involved in the early steps of IAA metabolism. These genes include a molybdenum cofactor-dependent dehydrogenase of the xanthine oxidase/aldehyde dehydrogenase family, a hydantoinase, a coenzyme A (CoA) ligase, a CoA transferase, a coenzyme B-12-dependent mutase, an acyl-CoA dehydrogenase, a fusion protein of an enoyl-CoA hydratase and a 3-hydroxyacyl-CoA dehydrogenase, a beta-ketothiolase, and a periplasmic substrate binding protein for ABC transport as well as a transcriptional regulator of the GntR family. Five predicted enzymes form or act on CoA thioesters, indicating that soon after the initial oxidation of IAA and possibly ring opening, CoA thioesters are formed, and the carbon skeleton is rearranged, followed by a CoA-dependent thiolytic release of another CoA thioester. We propose a scheme of an anaerobic IAA metabolic pathway that ultimately leads to 2-aminobenzoyl-CoA or benzoyl-CoA.