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X-ray structure of a Hg2+ complex of mercuric reductase (MerA) and quantum mechanical/molecular mechanical study of Hg2+ transfer between the C-terminal and buried catalytic site cysteine pairs.
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.
Afiliação
  • Lian P; The State Key Laboratory of Microbial Metabolism and College of Life Sciences and Biotechnology, Shanghai Jiao Tong University , Shanghai 200240, China.
Biochemistry ; 53(46): 7211-22, 2014 Nov 25.
Article em En | MEDLINE | ID: mdl-25343681
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.
Assuntos

Texto completo: 1 Base de dados: MEDLINE Assunto principal: Oxirredutases / Pseudomonas aeruginosa / Proteínas de Bactérias / Mercúrio Idioma: En Revista: Biochemistry Ano de publicação: 2014 Tipo de documento: Article País de afiliação: China

Texto completo: 1 Base de dados: MEDLINE Assunto principal: Oxirredutases / Pseudomonas aeruginosa / Proteínas de Bactérias / Mercúrio Idioma: En Revista: Biochemistry Ano de publicação: 2014 Tipo de documento: Article País de afiliação: China