Structure of ATP-bound human ATP:cobalamin adenosyltransferase
Structure of ATP-bound human ATP:cobalamin adenosyltransferase
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DOI：
10.1021/bi061396f
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发表时间：
2006-12-26
期刊：
影响因子：
2.9
通讯作者：
Hill, Christopher P.
中科院分区：
文献类型：
--
作者：
Schubert, Heidi L.;Hill, Christopher P.
编码人类ATP：钴胺腺苷转移酶(HATR)的基因突变会导致被称为甲基丙二酸尿症(MMA)的代谢紊乱。这种酶催化氰基钴胺(维生素B-12)转化为人体必需的辅因子腺苷钴胺的最后一步。在这里，我们提出了与HATR结合的ATP的2.5埃晶体结构，精炼到R值为25.2%。该酶形成一个紧密结合的三聚体，其中单体包括一个五螺旋束，活性部位位于亚基界面上。三聚体内的三个活性部位中只有两个含有结合的ATP底物，从而提供了同一晶体结构中脱氧核糖核酸和底物结合的活性部位的例子。比较空的和被占据的位置表明，酶的N-末端的20个残基在与ATP结合时变得有序，形成一个新的ATP结合部位和一个可能与钴胺结合的延伸裂隙。该结构解释了20个不变残基的作用；6个参与ATP结合，包括Arg190，它与剪切键两侧的ATP原子氢键。其中10个氢键是结构稳定所必需的，4个氢键处于与钴胺相互作用的位置。该结构还揭示了导致MMA的点突变是如何在这些功能上存在缺陷的。
Mutations in the gene encoding human ATP:cobalamin adenosyltransferase (hATR) can result in the metabolic disorder known as methylmalonic aciduria (MMA). This enzyme catalyzes the final step in the conversion of cyanocobalamin (vitamin B-12) to the essential human cofactor adenosylcobalamin. Here we present the 2.5 angstrom crystal structure of ATP bound to hATR refined to an R-free value of 25.2%. The enzyme forms a tightly associated trimer, where the monomer comprises a five-helix bundle and the active sites lie on the subunit interfaces. Only two of the three active sites within the trimer contain the bound ATP substrate, thereby providing examples of apo- and substrate-bound-active sites within the same crystal structure. Comparison of the empty and occupied sites indicates that twenty residues at the enzyme's N-terminus become ordered upon binding of ATP to form a novel ATP-binding site and an extended cleft that likely binds cobalamin. The structure explains the role of 20 invariant residues; six are involved in ATP binding, including Arg190, which hydrogen bonds to ATP atoms on both sides of the scissile bond. Ten of the hydrogen bonds are required for structural stability, and four are in positions to interact with cobalamin. The structure also reveals how the point mutations that cause MMA are deficient in these functions.