Synthesis Of C5-dicarboxylic acids from C2-units involving crotonyl-CoA carboxylase/reductase:: The ethylmalonyl-CoA pathway
Synthesis Of C5-dicarboxylic acids from C2-units involving crotonyl-CoA carboxylase/reductase:: The ethylmalonyl-CoA pathway
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DOI：
10.1073/pnas.0702791104
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发表时间：
2007-06-19
影响因子：
11.1
通讯作者：
Alber, Birgit E.
中科院分区：
文献类型：
--
作者：
Erb, Tobias J.;Berg, Ivan A.;Alber, Birgit E.
50年前，Kornberg和Krebs建立了乙醛酸循环作为c -2单位合成细胞成分的途径。然而，从那时起，许多细菌被描述为不含异柠檬酸裂解酶，这是该途径的关键酶。这里，一个途径称为乙基丙二酰辅酶a途径操作在这样的生物体被描述。同位素标记的醋酸盐和碳酸氢盐转化为乙基丙二酰辅酶a的细胞提取物的醋酸盐生长，异柠檬酸裂解酶阴性球形红杆菌通过核磁共振光谱测定。Crotonyl-CoA羧化酶/还原酶催化Crotonyl-CoA + CO2 + NADPH ->乙基丙二醇- coa (-) + NADP（+）是乙基丙二醇- coa途径的关键酶。烯基硫酯的还原羧基化是一种独特的生物化学反应，在生物学上是前所未有的。该酶在大肠杆菌中异种产生并进行了鉴定。Crotonyl-CoA羧化酶/还原酶（或其基因）可以作为乙丙二酰辅酶a途径存在的标志，该途径不仅在乙酰辅酶a同化中起作用。在链霉菌中，它也可以为抗生素的生物合成提供前体（乙基丙二酰辅酶a）。对于甲基营养细菌，如甲基细菌，通过乙基丙二酰辅酶a途径的反应延长丝氨酸循环，导致异柠檬酸裂解酶不依赖C-1同化的简化方案。
Fifty years ago, Kornberg and Krebs established the glyoxylate cycle as the pathway for the synthesis of cell constituents from C-2-units. However, since then, many bacteria have been described that do not contain isocitrate lyase, the key enzyme of this pathway. Here, a pathway termed the ethylmalonyl-CoA pathway operating in such organisms is described. Isotopically labeled acetate and bicarbonate were transformed to ethylmalonyl-CoA by cell extracts of acetate-grown, isocitrate lyase-negative Rhodobacter sphaeroides as determined by NMR spectroscopy. Crotonyl-CoA carboxylase/reductase, catalyzing crotonyl-CoA + CO2 + NADPH -> ethylmalonyl-CoA(-) + NADP(+) was identified as the key enzyme of the ethylmalonyl-CoA pathway. The reductive carboxylation of an enoyl-thioester is a unique biochemical reaction, unprecedented in biology. The enzyme from R. sphaeroides was heterologously produced in Escherichia coli and characterized. Crotonyl-CoA carboxylase/reductase (or its gene) can be used as a marker for the presence of the ethymalonyl-CoA pathway, which functions not only in acetyl-CoA assimilation. In Streptomyces sp., it may also supply precursors (ethylmalonyl-CoA) for antibiotic biosynthesis. For methylotrophic bacteria such as Methylobacterium extorquens, extension of the serine cycle with reactions of the ethylmalonyl-CoA pathway leads to a simplified scheme for isocitrate lyase-independent C-1 assimilation.