期刊
BIOCHEMISTRY
卷 53, 期 46, 页码 7211-7222出版社
AMER CHEMICAL SOC
DOI: 10.1021/bi500608u
关键词
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资金
- U.S. Department of Energy Office of Science [DE-FG03-01ER63087]
- Canada Research Chairs Program
- National Center for Research Resources, National Institute of Health [RR07707]
- Basic Energy Sciences, Office of Science, U.S. Department of Energy [W-31-109-Eng-38]
- U.S. Department of Energy (DOE) [DE-SC0004895]
- Shanghai Jiao Tong University
- Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231]
- National Institute of Computational Sciences [TG-MCA08X032]
- National High-Tech R&D Program (863 Program) [2012AA020307]
- National Basic Research Program of China (973 Program) [2012CB721000]
- Key Project of Shanghai Science and Technology Commission [11JC1406400]
- Ph.D. Programs Foundation of Ministry of Education of China [20120073110057]
- NATIONAL CENTER FOR RESEARCH RESOURCES [P41RR007707] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R24GM111072] Funding Source: NIH RePORTER
Mercuric reductase, MerA, is a key enzyme in bacterial mercury resistance. This homodimeric enzyme captures and reduces toxic Hg2+ to Hg-0, which is relatively unreactive and can exit the cell passively. Prior to reduction, the Hg2+ is transferred from a pair of cysteines (C558' and C559' using Tn501 numbering) at the C-terminus of one monomer to another pair of cysteines (C136 and C141) in the catalytic site of the other monomer. Here, we present the X-ray structure of the C-terminal Hg2+ complex of the C136A/C141A double mutant of the Tn501 MerA catalytic core and explore the molecular mechanism of this Hg transfer with quantum mechanical/molecular mechanical (QM/MM) calculations. The transfer is found to be nearly thermoneutral and to pass through a stable tricoordinated intermediate that is marginally less stable than the two end states. For the overall process, Hg2+ is always paired with at least two thiolates and thus is present at both the C-terminal and catalytic binding sites as a neutral complex. Prior to Hg2+ transfer, C141 is negatively charged. As Hg2+ is transferred into the catalytic site, a proton is transferred from C136 to C559' while C558' becomes negatively charged, resulting in the net transfer of a negative charge over a distance of similar to 7.5 angstrom. Thus, the transport of this soft divalent cation is made energetically feasible by pairing a competition between multiple Cys thiols and/or thiolates for Hg2+ with a competition between the Hg2+ and protons for the thiolates.
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