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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Structures of the N-terminal modules imply large domain motions during catalysis by methionine synthase
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Structures of the N-terminal modules imply large domain motions during catalysis by methionine synthase

机译：N末端模块的结构暗示蛋氨酸合酶催化过程中的大域运动。

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摘要

B-12-dependent methionine synthase (MetH) is a large modular enzyme that utilizes the cobalamin cofactor as a methyl donor or acceptor in three separate reactions. Each methyl transfer occurs at a different substrate-binding domain and requires a different arrangement of modules. In the catalytic cycle, the cobalamin-binding domain carries methylcobalamin to the homocysteine (Hcy) domain to form methionine and returns cob(I)alamin to the folate (Fol) domain for remethylation by methyltetra hydrofo late (CH3-H(4)folate). Here, we describe crystal structures of a fragment of MetH from Thermotoga maritima comprising the domains that bind Hcy and CH3-H(4)folate. These substrate-binding domains are (betaalpha)(8) barrels packed tightly against one another with their barrel axes perpendicular. The properties of the domain interface suggest that the two barrels remain associated during catalysis. The Hcy and CH3-H(4)folate substrates are bound at the C termini of their respective barrels in orientations that position them for reaction with cobalamin, but the two active sites are separated by approximate to50 Angstrom. To complete the catalytic cycle, the cobalamin-binding domain must travel back and forth between these distant active sites. [References: 46]
机译：B-12依赖的蛋氨酸合酶（MetH）是一种大型模块化酶，在三个独立的反应中利用钴胺素辅助因子作为甲基供体或受体。每次甲基转移发生在不同的底物结合域，并且需要不同的模块排列。在催化循环中，钴胺素结合结构域将甲基钴胺素携带至同型半胱氨酸（Hcy）域以形成蛋氨酸，并使钴（I）丙氨酸返回叶酸（Fol）域，以通过甲基四氢呋喃后期（CH3-H（4）folate）重新甲基化）。在这里，我们描述了来自滨海嗜热菌的MetH片段的晶体结构，包括结合Hcy和CH3-H（4）叶酸的域。这些底物结合域是彼此垂直排列的桶形β-（8）桶。域界面的性质表明，两个桶在催化过程中保持缔合。 Hcy和CH3-H（4）叶酸底物以其定位与钴胺素反应的方向在其相应桶的C末端结合，但两个活性位点相距约50埃。为了完成催化循环，钴胺素结合域必须在这些遥远的活性位点之间来回移动。 [参考：46]

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