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首页> 外文期刊>Journal of Molecular Biology >Structural basis for electron and methyl-group transfer in a methyltransferase system operating in the reductive acetyl-CoA pathway.
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Structural basis for electron and methyl-group transfer in a methyltransferase system operating in the reductive acetyl-CoA pathway.

机译：在还原性乙酰辅酶A途径中运行的甲基转移酶系统中电子和甲基转移的结构基础。

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Several anaerobic acetogenic, methanogenic, hydrogenogenic, and sulfate-reducing microorganisms are able to use the reductive acetyl-CoA (Wood-Ljungdahl) pathway to convert CO into biomass. The reductive acetyl-CoA pathway consists of two branches connected by the Co/Fe-containing corrinoid iron-sulfur protein (CoFeSP), which transfers a methyl group from a methyltransferase (MeTr)/methyltetrahydrofolate (CH-H folate) complex to the reduced Ni-Ni-[4Fe-4S] cluster (cluster A) of acetyl-CoA synthase. We investigated the CoFeSP and MeTr couple of the hydrogenogenic bacterium Carboxydothermus hydrogenoformans and show that the two proteins are able to catalyze the methyl-group transfer reaction from CH-H folate to the Co(I) center of CoFeSP. We determined the crystal structures of both proteins. The structure of CoFeSP includes the previously unresolved N-terminal domain of the large subunit of CoFeSP, revealing a unique four-helix-bundle-like architecture in which a [4Fe-4S] cluster is shielded by hydrophobic amino acids. It further reveals that the corrinoid and the [4Fe-4S] cluster binding domains are mobile, which is mandatory for the postulated electron transfer between them. Furthermore, we solved the crystal structures of apo-MeTr, CH-H-folate-bound MeTr, and H-folate-bound MeTr, revealing a substrate-induced closure of the CH-H folate binding cavity of MeTr. We observed three different conformations of Asn200 depending on the substrate bound in the active site, demonstrating its conformational modulation by hydrogen-bonding interactions with the substrate. The observed flexibility could be essential to stabilize the transition state during methyl-group transfer. The conformational space and role of Asn200 are likely conserved in homologous cobalamin-dependent MeTrs such as methionine synthase.
机译：数种厌氧产乙酸，产甲烷，产氢和硫酸盐还原微生物能够利用还原性乙酰辅酶A（Wood-Ljungdahl）途径将CO转化为生物质。还原性乙酰辅酶A途径由两个分支组成，这些分支由含钴/铁的类铁质铁硫蛋白（CoFeSP）连接，该分支将甲基从甲基转移酶（MeTr）/甲基四氢叶酸（CH-H叶酸）络合物转移到还原的乙酰辅酶A合酶的Ni-Ni- [4Fe-4S]簇（簇A）。我们调查了产氢细菌Carboxydothermus hydrooformans的CoFeSP和MeTr对，并表明这两种蛋白质能够催化从CH-H叶酸到CoFeSP的Co（I）中心的甲基转移反应。我们确定了两种蛋白质的晶体结构。 CoFeSP的结构包括CoFeSP大亚基的先前未解析的N末端结构域，揭示了独特的四螺旋束状结构，其中[4Fe-4S]簇被疏水氨基酸屏蔽。它进一步揭示了类固醇和[4Fe-4S]簇结合域是可移动的，这对于它们之间假定的电子转移是必不可少的。此外，我们解决了载脂蛋白-MeTr，CH-H-叶酸结合的MeTr和H-叶酸结合的MeTr的晶体结构，揭示了基质诱导的MeTr CH-H叶酸结合腔的封闭。我们观察到Asn200的三种不同构象，取决于结合在活性位点上的底物，证明了其通过与底物的氢键相互作用来构象调节。观察到的柔韧性对于稳定甲基转移过程中的过渡态可能至关重要。 Asn200的构象空间和作用很可能在依赖钴胺素的MeTrs（例如蛋氨酸合酶）中保守。

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