DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: X-ray Structure of a Hg 2+ Complex of Mercuric Reductase (MerA) and Quantum Mechanical/Molecular Mechanical Study of Hg 2+ Transfer between the C-Terminal and Buried Catalytic Site Cysteine Pairs

Abstract

Here we report that mercuric reductase, MerA, is a key enzyme in bacterial mercury resistance. This homodimeric enzyme captures and reduces toxic Hg2+ to Hg0, 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 netmore » transfer of a negative charge over a distance of ~7.5 Å. 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.« less

Authors:
 [1];  [2];  [2];  [3];  [4];  [5];  [6];  [7];  [5];  [2];  [2]
  1. The State Key Laboratory of Microbial Metabolism and College of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China, Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996, United States, UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
  2. Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996, United States, UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
  3. Department of Biochemistry and #Departments of Medical Biophysics and Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada
  4. UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
  5. The State Key Laboratory of Microbial Metabolism and College of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
  6. Department of Biochemistry and #Departments of Medical Biophysics and Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada, The Campbell Family Institute for Cancer Research, University Health Network, Toronto, Ontario M5G 1L7, Canada
  7. Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94158, United States
Publication Date:
Research Org.:
Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES); Canada Research Chairs Program; National Basic Research Program of China
OSTI Identifier:
1164539
Alternate Identifier(s):
OSTI ID: 1165617; OSTI ID: 1265925
Grant/Contract Number:  
FG03-01ER63087; SC0004895; FG03- 01ER63087; RR07707; W-31-109-Eng-38; AC02-05CH11231; TGMCA08X032; 2012CB721000; 11JC1406400; 20120073110057; AC05-00OR22725
Resource Type:
Published Article
Journal Name:
Biochemistry
Additional Journal Information:
Journal Name: Biochemistry Journal Volume: 53 Journal Issue: 46; Journal ID: ISSN 0006-2960
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES

Citation Formats

Lian, Peng, Guo, Hao-Bo, Riccardi, Demian, Dong, Aiping, Parks, Jerry M., Xu, Qin, Pai, Emil F., Miller, Susan M., Wei, Dong-Qing, Smith, Jeremy C., and Guo, Hong. X-ray Structure of a Hg 2+ Complex of Mercuric Reductase (MerA) and Quantum Mechanical/Molecular Mechanical Study of Hg 2+ Transfer between the C-Terminal and Buried Catalytic Site Cysteine Pairs. United States: N. p., 2014. Web. doi:10.1021/bi500608u.
Lian, Peng, Guo, Hao-Bo, Riccardi, Demian, Dong, Aiping, Parks, Jerry M., Xu, Qin, Pai, Emil F., Miller, Susan M., Wei, Dong-Qing, Smith, Jeremy C., & Guo, Hong. X-ray Structure of a Hg 2+ Complex of Mercuric Reductase (MerA) and Quantum Mechanical/Molecular Mechanical Study of Hg 2+ Transfer between the C-Terminal and Buried Catalytic Site Cysteine Pairs. United States. https://doi.org/10.1021/bi500608u
Lian, Peng, Guo, Hao-Bo, Riccardi, Demian, Dong, Aiping, Parks, Jerry M., Xu, Qin, Pai, Emil F., Miller, Susan M., Wei, Dong-Qing, Smith, Jeremy C., and Guo, Hong. Thu . "X-ray Structure of a Hg 2+ Complex of Mercuric Reductase (MerA) and Quantum Mechanical/Molecular Mechanical Study of Hg 2+ Transfer between the C-Terminal and Buried Catalytic Site Cysteine Pairs". United States. https://doi.org/10.1021/bi500608u.
@article{osti_1164539,
title = {X-ray Structure of a Hg 2+ Complex of Mercuric Reductase (MerA) and Quantum Mechanical/Molecular Mechanical Study of Hg 2+ Transfer between the C-Terminal and Buried Catalytic Site Cysteine Pairs},
author = {Lian, Peng and Guo, Hao-Bo and Riccardi, Demian and Dong, Aiping and Parks, Jerry M. and Xu, Qin and Pai, Emil F. and Miller, Susan M. and Wei, Dong-Qing and Smith, Jeremy C. and Guo, Hong},
abstractNote = {Here we report that mercuric reductase, MerA, is a key enzyme in bacterial mercury resistance. This homodimeric enzyme captures and reduces toxic Hg2+ to Hg0, 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 ~7.5 Å. 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.},
doi = {10.1021/bi500608u},
journal = {Biochemistry},
number = 46,
volume = 53,
place = {United States},
year = {Thu Nov 13 00:00:00 EST 2014},
month = {Thu Nov 13 00:00:00 EST 2014}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1021/bi500608u

Citation Metrics:
Cited by: 36 works
Citation information provided by
Web of Science

Save / Share: