X-ray Absorption Spectroscopy Reveals an Organometallic Ni-C Bond in the CO-Treated Form of Acetyl-CoA Synthase.
X-ray Absorption Spectroscopy Reveals an Organometallic Ni-C Bond in the CO-Treated Form of Acetyl-CoA Synthase.
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DOI：
10.1021/acs.biochem.6b00983
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发表时间：
2017-03-07
期刊：
影响因子：
2.9
通讯作者：
Sarangi R
中科院分区：
文献类型：
--
作者：
Can M;Giles LJ;Ragsdale SW;Sarangi R
乙酰辅酶A合成酶（acetyl-CoA synthase，ACS）是Wood-Ljungdahl厌氧CO2固定途径中的关键酶，其作用机制涉及一系列与蛋白质结合的有机金属（Ni-CO，methyl-Ni，acetyl-Ni）中间体。在这里，我们报告的第一个直接的结构证据的建议金属碳键。我们描述了高活性的金属充满酶和近定量生成的动力学主管羰基化中间体的制备。这一进展使得镍和铁的K边X射线吸收光谱和扩展的X射线吸收精细结构实验沿着与密度泛函理论计算相结合。数据表明，CO结合到近端的Ni的六金属中心的活性位点，并经历了戏剧性的结构和电子扰动，形成这种有机金属Ni-CO中间体。这种直接鉴定的镍-碳键的催化活性的CO结合形式的A簇的ACS提供了明确的实验结构证据，支持提出的有机金属机制的厌氧乙酰辅酶A合成。
Acetyl-CoA synthase (ACS) is a key enzyme in the Wood–Ljungdahl pathway of anaerobic CO2 fixation, which has long been proposed to operate by a novel mechanism involving a series of protein-bound organometallic (Ni–CO, methyl–Ni, and acetyl–Ni) intermediates. Here we report the first direct structural evidence of the proposed metal–carbon bond. We describe the preparation of the highly active metal-replete enzyme and near-quantitative generation of the kinetically competent carbonylated intermediate. This advance has allowed a combination of Ni and Fe K-edge X-ray absorption spectroscopy and extended X-ray absorption fine structure experiments along with density functional theory calculations. The data reveal that CO binds to the proximal Ni of the six-metal metallocenter at the active site and undergoes dramatic structural and electronic perturbation in forming this organometallic Ni–CO intermediate. This direct identification of a Ni–carbon bond in the catalytically competent CO-bound form of the A cluster of ACS provides definitive experimental structural evidence supporting the proposed organometallic mechanism of anaerobic acetyl-CoA synthesis.
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