Mercury (Hg) is a heavy metal that exhibits high biological toxicity. Monomethylmercury and dimethylmercury are neurotoxins and a significant environmental concern as they bioaccumulate and biomagnify within the aquatic food web. Microbial Hg methylation involves two proteins, HgcA and HgcB. Here, we show that HgcA and HgcB can be heterologously coexpressed, and the HgcAB complex can be purified. We demonstrated that HgcA is a membrane-associated cobalamin-dependent methyltransferase and HgcB is a ferredoxin-like protein containing two [4Fe-4S] clusters. Further, spectroscopic and kinetic results demonstrate that S-adenosyl-L-methionine (SAM) donates the methyl group to Hg in a two-step reaction involving a methylcob(III)alamin intermediate including Co-thiolate ligation from a conserved Cys residue. Our findings uncover a biological role for SAM in microbial Hg methylation.

中文翻译：

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S-腺苷-L-蛋氨酸是膜相关 HgcAB 复合物甲基化汞的意外甲基供体


汞 （Hg） 是一种具有高生物毒性的重金属。一甲基汞和二甲基汞是神经毒素，在水生食物网中生物积累和生物放大，因此对环境构成重大影响。微生物 Hg 甲基化涉及两种蛋白质，HgcA 和 HgcB。在这里，我们表明 HgcA 和 HgcB 可以异源共表达，并且 HgcAB 复合物可以被纯化。我们证明 HgcA 是一种膜相关的钴胺依赖性甲基转移酶，HgcB 是一种包含两个 [4Fe-4S] 簇的铁氧还蛋白样蛋白。此外，光谱和动力学结果表明，S-腺苷-L-蛋氨酸 （SAM） 在涉及甲基 cob（III）alamin 中间体的两步反应中将甲基提供给 Hg，包括来自保守 Cys 残基的共硫代化连接。我们的研究结果揭示了 SAM 在微生物 Hg 甲基化中的生物学作用。