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首页> 外文期刊>Journal of Molecular Biology >Elucidations of the catalytic cycle of NADH-cytochrome b5 reductase by X-ray crystallography: New insights into regulation of efficient electron transfer
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Elucidations of the catalytic cycle of NADH-cytochrome b5 reductase by X-ray crystallography: New insights into regulation of efficient electron transfer

机译：X射线晶体学阐明NADH-细胞色素b5还原酶的催化循环：调节有效电子转移的新见解

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摘要

NADH-Cytochrome b5 reductase (b5R), a flavoprotein consisting of NADH and flavin adenine dinucleotide (FAD) binding domains, catalyzes electron transfer from the two-electron carrier NADH to the one-electron carrier cytochrome b5 (Cb5). The crystal structures of both the fully reduced form and the oxidized form of porcine liver b5R were determined. In the reduced b5R structure determined at 1.68 ? resolution, the relative configuration of the two domains was slightly shifted in comparison with that of the oxidized form. This shift resulted in an increase in the solvent-accessible surface area of FAD and created a new hydrogen-bonding interaction between the N5 atom of the isoalloxazine ring of FAD and the hydroxyl oxygen atom of Thr66, which is considered to be a key residue in the release of a proton from the N5 atom. The isoalloxazine ring of FAD in the reduced form is flat as in the oxidized form and stacked together with the nicotinamide ring of NAD+. Determination of the oxidized b5R structure, including the hydrogen atoms, determined at 0.78 ? resolution revealed the details of a hydrogen-bonding network from the N5 atom of FAD to His49 via Thr66. Both of the reduced and oxidized b5R structures explain how backflow in this catalytic cycle is prevented and the transfer of electrons to one-electron acceptors such as Cb5 is accelerated. Furthermore, crystallographic analysis by the cryo-trapping method suggests that re-oxidation follows a two-step mechanism. These results provide structural insights into the catalytic cycle of b5R.
机译：NADH细胞色素b5还原酶（b5R）是由NADH和黄素腺嘌呤二核苷酸（FAD）结合域组成的黄素蛋白，催化电子从两电子载体NADH转移到单电子载体细胞色素b5（Cb5）。测定了猪肝b5R的完全还原形式和氧化形式的晶体结构。在还原的b5R结构中确定为1.68≤m。在分辨率上，与氧化形式相比，两个结构域的相对构型略有偏移。这种转变导致FAD的溶剂可及表面积增加，并在FAD的异别恶嗪环的N5原子与Thr66的羟基氧原子之间建立了新的氢键相互作用，Thr66的羟基残基被认为是其中的关键残基。 N5原子释放出质子还原形式的FAD的异恶嗪环与氧化态一样平坦，并与NAD +的烟酰胺环堆叠在一起。确定氧化的b5R结构（包括氢原子）为0.78？分辨率揭示了从FAD的N5原子通过Thr66到His49的氢键网络的细节。还原和氧化的b5R结构都解释了如何防止此催化循环中的回流以及如何加速电子向单电子受体（如Cb5）的转移。此外，通过冷阱法的晶体学分析表明，再氧化遵循两步机制。这些结果提供了对b5R催化循环的结构见解。

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