New reactions in the crotonase superfamily:: Structure of methylmalonyl CoA decarboxylase from Escherichia coli
New reactions in the crotonase superfamily:: Structure of methylmalonyl CoA decarboxylase from Escherichia coli
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DOI：
10.1021/bi9928896
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发表时间：
2000-04-25
期刊：
影响因子：
2.9
通讯作者：
Holden, HM
中科院分区：
文献类型：
--
作者：
Benning, MM;Haller, T;Holden, HM
甲基丙二酸单酰 CoA 脱羧酶 (MMCD) 是由大肠杆菌基因组编码的巴豆酸酶超家族的新定义成员，已通过 X 射线晶体学分析解析出其未配体形式的分辨率为 1.85 埃，以及与惰性硫醚类似物的福拉复合物的分辨率为 2.7 埃。 甲基丙二酰辅酶A。与巴豆酸酶超家族的其他两个结构特征成员（巴豆酸酶和二烯酰辅酶 A 异构酶）一样，MMCD 是六聚体（三聚体的二聚体），每个多肽链由两个结构基序组成。较大的 N 端结构域包含活性位点，而较小的 C 端基序是 ct 螺旋，主要参与三聚化。然而，与巴豆酶超家族的其他成员不同，C 端基序折叠回 N 端结构域，使得每个活性位点完全包含在单个亚基内。甲基丙二酰辅酶 A 的硫醚类似物的羧酸根与 Gly 110 的肽 NH 基团和 His 66 的咪唑环形成氢键。从模型研究来看，Tyr 140 位于活性位点内，通过定向甲基丙二酰辅酶 A 的羧酸根使其与硫酯平面正交，参与脱羧反应。 羰基。令人惊讶的是，虽然MMCD的活性位点含有Glu 113，与巴豆酸酶活性位点中的一般酸/碱Glu 144同源，但其羧酸侧链与Arg X6形成氢键，表明其不直接参与催化。在 MMCD 活性位点观察到的新推定功能组群强调了该超家族功能的多样性。
The molecular structure of methylmalonyl CoA decarboxylase (MMCD), a newly defined member of the crotonase superfamily encoded by the Escherichia coli genome, has been solved by X-ray crystallographic analyses to a resolution of 1.85 Angstrom for the unliganded form and to a resolution of 2.7 Angstrom fora complex with an inert thioether analogue of methylmalonyl CoA. Like two other structurally characterized members of the crotonase superfamily (crotonase and dienoyl CoA isomerase), MMCD is a hexamer (dimer of trimers) with each polypeptide chain composed of two structural motifs. The larger N-terminal domain contains the active site while the smaller C-terminal motif is ct-helical and involved primarily in trimerization, Unlike the other members of the crotonase superfamily, however, the C-terminal motif is folded back onto the N-terminal domain such that each active site is wholly contained within a single subunit. The carboxylate group of the thioether analogue of methylmalonyl CoA is hydrogen bonded to the peptidic NH group of Gly 110 and the imidazole ring of His 66. From modeling studies, it appears that Tyr 140 is positioned within the active site to participate in the decarboxylation reaction by orienting the carboxylate group of methylmalonyl CoA so that it is orthogonal to the plane of the thioester carbonyl group. Surprisingly, while the active site of MMCD contains Glu 113, which is homologous to the general acid/base Glu 144 in the active site of crotonase, its carboxylate side chain is hydrogen bonded to Arg X6, suggesting that it is not directly involved in catalysis. The new constellation of putative functional groups observed in the active site of MMCD underscores the diversity of function in this superfamily.