Broad substrate specificity of phosphotransbutyrylase from Listeria monocytogenes: A potential participant in an alternative pathway for provision of acyl CoA precursors for fatty acid biosynthesis.
Broad substrate specificity of phosphotransbutyrylase from Listeria monocytogenes: A potential participant in an alternative pathway for provision of acyl CoA precursors for fatty acid biosynthesis.
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DOI：
10.1016/j.bbalip.2016.06.003
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发表时间：
2016-09
期刊：
影响因子：
--
通讯作者：
Gatto C
中科院分区：
文献类型：
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作者：
Sirobhushanam S;Galva C;Sen S;Wilkinson BJ;Gatto C
单核细胞增生李斯特菌是严重食源性疾病李斯特菌病的致病菌，其膜上富含支链脂肪酸（BCFAs）。BCFA通常是由支链氨基酸通过支链α-酮酸脱氢酶（Bkd）的活性合成的，该途径的破坏导致膜中BCFA含量的降低。短支链羧酸（BCCAs）作为培养基添加，导致BCCAs在单核增生乳杆菌bkd突变体MOR401的膜中掺入。高浓度的补品也会对具有完整bkd的野生型生物体的膜产生类似的变化。这些羧酸显然是脂肪酸的前体，一定有另一种途径导致它们的辅酶a硫酯衍生物的形成。候选酶是磷酸转丁基化酶（Ptb）和丁酸激酶（Buk），它们是bkd操纵子的前两个基因的产物。来自单核增生乳杆菌的Ptb表现出广泛的底物特异性，对支链底物有强烈的偏好，对乙酰辅酶a和己醇辅酶a缺乏活性，对链长有严格的偏好（C3-C5）。Ptb催化作用涉及三元络合物的形成。此外，Ptb可以利用非天然的支链底物，如2-乙基丁基辅酶a，尽管效率较低，但与该酶可能参与将羧酸添加剂转化为BCFA生物合成的辅酶a引物相一致。
Listeria monocytogenes, the causative organism of the serious food-borne disease listeriosis, has a membrane abundant in branched-chain fatty acids (BCFAs). BCFAs are normally biosynthesized from branched-chain amino acids via the activity of branched chain α-keto acid dehydrogenase (Bkd), and disruption of this pathway results in reduced BCFA content in the membrane. Short branched-chain carboxylic acids (BCCAs) added as media supplements result in incorporation of BCFAs arising from the supplemented BCCAs in the membrane of L. monocytogenes bkd mutant MOR401. High concentrations of the supplements also effect similar changes in the membrane of the wild type organism with intact bkd. Such carboxylic acids clearly act as fatty acid precursors, and there must be an alternative pathway resulting in the formation of their CoA thioester derivatives. Candidates for this are the enzymes phosphotransbutyrylase (Ptb) and butyrate kinase (Buk), the products of the first two genes of the bkd operon. Ptb from L. monocytogenes exhibited broad substrate specificity, a strong preference for branched-chain substrates, a lack of activity with acetyl CoA and hexanoyl CoA, and strict chain length preference (C3–C5). Ptb catalysis involved ternary complex formation. Additionally, Ptb could utilize unnatural branched-chain substrates such as 2-ethylbutyryl CoA, albeit with lower efficiency, consistent with a potential involvement of this enzyme in the conversion of the carboxylic acid additives into CoA primers for BCFA biosynthesis.