Cooper Connor J, Zheng Kaiyuan, Rush Katherine W, Johs Alexander, Sanders Brian C, Pavlopoulos Georgios A, Kyrpides Nikos C, Podar Mircea, Ovchinnikov Sergey, Ragsdale Stephen W, Parks Jerry M
Graduate School of Genome Science and Technology, University of Tennessee, F225 Walters Life Science, Knoxville, TN, 37996, USA.
Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, 37831-6038, USA.
Commun Biol. 2020 Jun 19;3(1):320. doi: 10.1038/s42003-020-1047-5.
Bacteria and archaea possessing the hgcAB gene pair methylate inorganic mercury (Hg) to form highly toxic methylmercury. HgcA consists of a corrinoid binding domain and a transmembrane domain, and HgcB is a dicluster ferredoxin. However, their detailed structure and function have not been thoroughly characterized. We modeled the HgcAB complex by combining metagenome sequence data mining, coevolution analysis, and Rosetta structure calculations. In addition, we overexpressed HgcA and HgcB in Escherichia coli, confirmed spectroscopically that they bind cobalamin and [4Fe-4S] clusters, respectively, and incorporated these cofactors into the structural model. Surprisingly, the two domains of HgcA do not interact with each other, but HgcB forms extensive contacts with both domains. The model suggests that conserved cysteines in HgcB are involved in shuttling Hg, methylmercury, or both. These findings refine our understanding of the mechanism of Hg methylation and expand the known repertoire of corrinoid methyltransferases in nature.
拥有hgcAB基因对的细菌和古菌会将无机汞（Hg）甲基化，形成剧毒的甲基汞。HgcA由一个类咕啉结合结构域和一个跨膜结构域组成，HgcB是一个双簇铁氧化还原蛋白。然而，它们的详细结构和功能尚未得到充分表征。我们通过整合宏基因组序列数据挖掘、共进化分析和罗塞塔结构计算，对HgcAB复合物进行了建模。此外，我们在大肠杆菌中过表达了HgcA和HgcB，通过光谱学证实它们分别结合钴胺素和[4Fe-4S]簇，并将这些辅因子纳入结构模型。令人惊讶的是，HgcA的两个结构域彼此不相互作用，但HgcB与这两个结构域都形成了广泛的接触。该模型表明，HgcB中保守的半胱氨酸参与汞、甲基汞或两者的穿梭运输。这些发现深化了我们对汞甲基化机制的理解，并扩展了自然界中已知的类咕啉甲基转移酶种类。
