Structural insight on the mechanism of an electron-bifurcating [FeFe] hydrogenase.
Structural insight on the mechanism of an electron-bifurcating [FeFe] hydrogenase.
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DOI：
10.7554/elife.79361
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发表时间：
2022-08-26
期刊：
影响因子：
7.7
通讯作者：
Birrell, James A.
中科院分区：
文献类型：
--
作者：
Furlan, Chris;Chongdar, Nipa;Gupta, Pooja;Lubitz, Wolfgang;Ogata, Hideaki;Blaza, James N.;Birrell, James A.
电子分叉是自然界中基本的能量守恒机制，其中来自中间电势电子供体的两个电子被分裂，使得一个沿着高电势路径发送到高电势受体，另一个沿着低电势路径发送到低电势受体。该过程允许放能反应驱动的放能反应，是一种替代的，较少认识到，能量耦合到众所周知的化学渗透原理的机制。来自海栖热袍菌（Thermotoga maritima）的电子分叉[FeFe]氢化酶（HydABC）需要NADH和铁氧还蛋白两者来还原质子以产生氢。尽管过去几年进行了大量的研究，但HydABC中电子分岔的机制仍然是个谜。结构信息可以为更好地理解光谱和功能信息提供基础。在这里，我们提出了一个2.3纳米的电子冷冻显微镜结构的HydABC。该结构显示了由两个独立的“半”组成的杂十二聚体，每个半“由通过[4Fe-4S]簇连接的两个强相互作用的HydABC异源三聚体组成。中心电子转移途径连接NADH氧化和质子还原的活性位点。我们确定了一个灵活的铁硫簇域的两种构象：一个“闭桥”和一个“开桥”的构象，其中的Zn 2+网站可以作为一个“铰链”允许域运动。基于这些结构的启示，我们提出了一个可能的机制，电子分叉在HydABC的黄素monopolytide作为电子分叉中心和作为NAD+还原/NADH氧化位点的双重作用。
Electron bifurcation is a fundamental energy conservation mechanism in nature in which two electrons from an intermediate-potential electron donor are split so that one is sent along a high-potential pathway to a high-potential acceptor and the other is sent along a low-potential pathway to a low-potential acceptor. This process allows endergonic reactions to be driven by exergonic ones and is an alternative, less recognized, mechanism of energy coupling to the well-known chemiosmotic principle. The electron-bifurcating [FeFe] hydrogenase from Thermotoga maritima (HydABC) requires both NADH and ferredoxin to reduce protons generating hydrogen. The mechanism of electron bifurcation in HydABC remains enigmatic in spite of intense research efforts over the last few years. Structural information may provide the basis for a better understanding of spectroscopic and functional information. Here, we present a 2.3 Å electron cryo-microscopy structure of HydABC. The structure shows a heterododecamer composed of two independent ‘halves’ each made of two strongly interacting HydABC heterotrimers connected via a [4Fe–4S] cluster. A central electron transfer pathway connects the active sites for NADH oxidation and for proton reduction. We identified two conformations of a flexible iron–sulfur cluster domain: a ‘closed bridge’ and an ‘open bridge’ conformation, where a Zn2+ site may act as a ‘hinge’ allowing domain movement. Based on these structural revelations, we propose a possible mechanism of electron bifurcation in HydABC where the flavin mononucleotide serves a dual role as both the electron bifurcation center and as the NAD+ reduction/NADH oxidation site.