Abstract
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 HgII, methylmercury, or both. These findings refine our understanding of the mechanism of Hg methylation and expand the known repertoire of corrinoid methyltransferases in nature.
| Original language | English |
|---|---|
| Article number | 320 |
| Journal | Communications Biology |
| Volume | 3 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 1 2020 |
Funding
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, through the Mercury Scientific Focus Area Program at Oak Ridge National Laboratory (ORNL) and the Laboratory Directed Research and Development program at ORNL, which is managed by UT Battelle, LLC, for DOE under contract DE-AC05–00OR22725. C.J.C. was supported by a National Science Foundation Graduate Research Fellowship under Grant No. 2017219379. S.W.R. was supported by NIH NIGMS grant R01GM124174. SO was supported by NIH grant DP5OD026389. G.A.P. and N.C.K. were supported by the U.S. DOE Joint Genome Institute, a DOE Office of Science User Facility, under contract no. DE-AC02-05CH11231 and used resources of the National Energy Research Scientific Computing Center, which is supported by the DOE Office of Science under contract no. DE-AC02-05CH11231. G.A.P. was also supported by the Hellenic Foundation for Research and Innovation (H.F.R.I) under the “First Call for H.F.R.I Research Projects to support faculty members and researchers and the procurement of high-cost research equipment grant”, Grant ID: 1855-BOLOGNA. This research used resources at the Compute and Data Environment for Science (CADES) at ORNL. J.M.P. thanks J. Banfield for help with preliminary sequence searches.