Bacterial variations on the methionine salvage pathway -: art. no. 9
Bacterial variations on the methionine salvage pathway -: art. no. 9
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DOI：
10.1186/1471-2180-4-9
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发表时间：
2004-03-04
期刊：
影响因子：
4.2
通讯作者：
Danchin, A
中科院分区：
文献类型：
--
作者：
Sekowska, A;Dénervaud, V;Danchin, A
背景：S-腺苷甲硫氨酸的硫甲基通常从甲硫腺苷中回收为甲硫氨酸。枯草芽孢杆菌中相应的途径已被阐明。然而，根据生物体的不同，甲硫腺苷会经历替代的降解途径。结果：这项工作使用计算机基因组分析提出了肺炎克雷伯菌、问号钩端螺旋体、腾康热厌氧杆菌和苛养木杆菌的蛋氨酸挽救途径。用枯草芽孢杆菌和铜绿假单胞菌突变体进行的实验证实了所提出的假设。催化反应的酶来自不同的来源。该途径中第一个普遍存在的酶 MtnA（甲基硫核糖-1-磷酸异构酶）属于与真核起始因子 2B α 相关的蛋白质家族。 mtnB 编码甲基硫核酮糖-1-磷酸脱水酶。随后发生两个反应，即烯醇酶反应和磷酸酶反应。虽然在枯草芽孢杆菌中，这是由两种不同的多肽完成的，但在此处分析的其他生物体中，烯醇化磷酸酶产生 1,2-二羟基-3-酮-5-甲基硫代戊烯。在双氧存在下，酸还原酮双加氧酶产生甲硫氨酸的直接前体酮甲基硫代丁酸。在某些条件下，这种酶会在枯草芽孢杆菌中产生一氧化碳，这为细菌中新的气体介质提供了一条途径。酮甲基硫代丁酸最终被转氨酶转氨，转氨酶通常作为广泛特异性酶存在（通常能够转氨芳香族氨基酸酮酸前体或组氨醇磷酸）。 结论：首次在铜绿假单胞菌中通过实验证明了功能性蛋氨酸补救途径。显然，蛋氨酸补救途径在细菌（和真核生物）中很常见，通过招募不同的多肽来执行所需的反应（翻译起始因子和RuBisCO的祖先，在一些厚壁菌门中作为烯醇化酶）。许多细菌高度依赖于氧气的存在，这表明生态位可能对该途径的存在和/或代谢步骤发挥重要作用，即使在系统发育相关的细菌中也是如此。需要进一步的工作来揭示当双氧稀缺或不存在时的相应步骤（这对于探索古生菌中该途径的存在非常重要）。在没有氧气的情况下茁壮成长的嗜热T. tengcongensis似乎拥有这条途径。这将是揭示厌氧环境中缺失反应的一个有趣的链接。
Background: The thiomethyl group of S-adenosylmethionine is often recycled as methionine from methylthioadenosine. The corresponding pathway has been unravelled in Bacillus subtilis. However methylthioadenosine is subjected to alternative degradative pathways depending on the organism.Results: This work uses genome in silico analysis to propose methionine salvage pathways for Klebsiella pneumoniae, Leptospira interrogans, Thermoanaerobacter tengcongensis and Xylella fastidiosa. Experiments performed with mutants of B. subtilis and Pseudomonas aeruginosa substantiate the hypotheses proposed. The enzymes that catalyze the reactions are recruited from a variety of origins. The first, ubiquitous, enzyme of the pathway, MtnA (methylthioribose-1-phosphate isomerase), belongs to a family of proteins related to eukaryotic intiation factor 2B alpha. mtnB codes for a methylthioribulose-1-phosphate dehydratase. Two reactions follow, that of an enolase and that of a phosphatase. While in B. subtilis this is performed by two distinct polypeptides, in the other organisms analyzed here an enolase-phosphatase yields 1,2-dihydroxy-3-keto-5-methylthiopentene. In the presence of dioxygen an aci-reductone dioxygenase yields the immediate precursor of methionine, ketomethylthiobutyrate. Under some conditions this enzyme produces carbon monoxide in B. subtilis, suggesting a route for a new gaseous mediator in bacteria. Ketomethylthiobutyrate is finally transaminated by an aminotransferase that exists usually as a broad specificity enzyme (often able to transaminate aromatic aminoacid keto-acid precursors or histidinol-phosphate).Conclusion: A functional methionine salvage pathway was experimentally demonstrated, for the first time, in P. aeruginosa. Apparently, methionine salvage pathways are frequent in Bacteria ( and in Eukarya), with recruitment of different polypeptides to perform the needed reactions (an ancestor of a translation initiation factor and RuBisCO, as an enolase, in some Firmicutes). Many are highly dependent on the presence of oxygen, suggesting that the ecological niche may play an important role for the existence and/or metabolic steps of the pathway, even in phylogenetically related bacteria. Further work is needed to uncover the corresponding steps when dioxygen is scarce or absent (this is important to explore the presence of the pathway in Archaea). The thermophile T. tengcongensis, that thrives in the absence of oxygen, appears to possess the pathway. It will be an interesting link to uncover the missing reactions in anaerobic environments.