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首页> 外文期刊>Journal of Molecular Biology >The Cobalamin-Independent Methionine Synthase Enzyme Captured in a Substrate-Induced Closed Conformation
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The Cobalamin-Independent Methionine Synthase Enzyme Captured in a Substrate-Induced Closed Conformation

机译：基质诱导的封闭构象中捕获的钴胺素非依赖性蛋氨酸合酶。

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The cobalamin-independent methionine synthase enzyme catalyzes a challenging reaction: the direct transfer of a methyl from 5-methyl-tetrahydrofolate-glutamate(3) to the L-homocysteine thiol. The enzyme has a dual (beta alpha)(8) TIM barrel structure that binds, activates and brings the reactants into reaction proximity by conformational movements. In the previously observed open structures, the substrates bind too far apart to react, but we have captured a ternary complex with both substrates bound in a closed form of the enzyme. The closing is described in terms of a hinge between the N-and C-terminal TIM barrels and a rearrangement of key loops within the C domain. The substrate specificity can now be rationalized and the structure reveals His707 as the acid that protonates the THF leaving group through a water molecule trapped in the closed active site. The substrates are correctly oriented for an in-line attack by L-homocysteine on the N-5-methyl. (C) 2015 Elsevier Ltd. All rights reserved.
机译：不依赖钴胺素的甲硫氨酸合酶催化一个具有挑战性的反应：甲基直接从5-甲基-四氢叶酸-谷氨酸（3）转移到L-高半胱氨酸硫醇。该酶具有双重（βalpha）（8）TIM桶状结构，可通过构象运动结合，激活反应物并使反应物进入反应附近。在先前观察到的开放结构中，底物结合得太远而无法反应，但是我们捕获了三元复合物，两个底物均以封闭形式的酶结合。根据N端和C端TIM枪管之间的铰链以及C域内键环的重新排列来描述闭合。现在可以合理化底物特异性，该结构揭示了His707，它是一种酸，该酸通过捕获在封闭的活性位点中的水分子使THF离开的基团质子化。底物的方向正确，可被L-高半胱氨酸在线攻击N-5-甲基。 （C）2015 Elsevier Ltd.保留所有权利。

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