Welbio and the Laboratory of Physiological Chemistry, Université Catholique de Louvain, 1200 Brussels, Belgium.
J Biol Chem. 2011 Dec 16;286(50):42992-3003. doi: 10.1074/jbc.M111.281527. Epub 2011 Oct 20.
A limited number of enzymes are known that play a role analogous to DNA proofreading by eliminating non-classical metabolites formed by side activities of enzymes of intermediary metabolism. Because few such "metabolite proofreading enzymes" are known, our purpose was to search for an enzyme able to degrade ethylmalonyl-CoA, a potentially toxic metabolite formed at a low rate from butyryl-CoA by acetyl-CoA carboxylase and propionyl-CoA carboxylase, two major enzymes of lipid metabolism. We show that mammalian tissues contain a previously unknown enzyme that decarboxylates ethylmalonyl-CoA and, at lower rates, methylmalonyl-CoA but that does not act on malonyl-CoA. Ethylmalonyl-CoA decarboxylase is particularly abundant in brown adipose tissue, liver, and kidney in mice, and is essentially cytosolic. Because Escherichia coli methylmalonyl-CoA decarboxylase belongs to the family of enoyl-CoA hydratase (ECH), we searched mammalian databases for proteins of uncharacterized function belonging to the ECH family. Combining this database search approach with sequencing data obtained on a partially purified enzyme preparation, we identified ethylmalonyl-CoA decarboxylase as ECHDC1. We confirmed this identification by showing that recombinant mouse ECHDC1 has a substantial ethylmalonyl-CoA decarboxylase activity and a lower methylmalonyl-CoA decarboxylase activity but no malonyl-CoA decarboxylase or enoyl-CoA hydratase activity. Furthermore, ECHDC1-specific siRNAs decreased the ethylmalonyl-CoA decarboxylase activity in human cells and increased the formation of ethylmalonate, most particularly in cells incubated with butyrate. These findings indicate that ethylmalonyl-CoA decarboxylase may correct a side activity of acetyl-CoA carboxylase and suggest that its mutation may be involved in the development of certain forms of ethylmalonic aciduria.
已知有少数酶在消除中间代谢酶的侧活性形成的非典型代谢物方面发挥类似于 DNA 校对的作用。由于已知的此类“代谢物校对酶”很少，我们的目的是寻找一种能够降解乙基丙二酰辅酶 A 的酶，乙基丙二酰辅酶 A 是由乙酰辅酶 A 羧化酶和丙二酰辅酶 A 羧化酶这两种脂质代谢的主要酶以低速率形成的潜在有毒代谢物。我们表明，哺乳动物组织中含有一种以前未知的酶，该酶可使乙基丙二酰辅酶 A 脱羧，并且以较低的速率使甲基丙二酰辅酶 A 脱羧，但不能使丙二酰辅酶 A 脱羧。乙基丙二酰辅酶 A 脱羧酶在小鼠的棕色脂肪组织、肝脏和肾脏中特别丰富，主要存在于细胞质中。由于大肠杆菌甲基丙二酰辅酶 A 脱羧酶属于烯酰辅酶 A 水合酶（ECH）家族，我们在哺乳动物数据库中搜索了属于 ECH 家族的未鉴定功能的蛋白质。将这种数据库搜索方法与部分纯化酶制剂获得的测序数据相结合，我们将乙基丙二酰辅酶 A 脱羧酶鉴定为 ECHDC1。我们通过证明重组小鼠 ECHDC1 具有相当大的乙基丙二酰辅酶 A 脱羧酶活性和较低的甲基丙二酰辅酶 A 脱羧酶活性，但没有丙二酰辅酶 A 脱羧酶或烯酰辅酶 A 水合酶活性来证实这一鉴定。此外，ECHDC1 特异性 siRNA 降低了人细胞中乙基丙二酰辅酶 A 脱羧酶的活性，并增加了乙基丙二酸的形成，尤其是在与丁酸盐孵育的细胞中。这些发现表明，乙基丙二酰辅酶 A 脱羧酶可能纠正乙酰辅酶 A 羧化酶的侧活性，并表明其突变可能与某些形式的乙基丙二酸尿症的发展有关。
