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Journal of Bacteriology, December 2003, p. 6780-6789, Vol. 185, No. 23
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.23.6780-6789.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

An Arsenate Reductase from Synechocystis sp. Strain PCC 6803 Exhibits a Novel Combination of Catalytic Characteristics

Renhui Li,1 January D. Haile,2 and Peter J. Kennelly1*

Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061,1 Departments of Biology and Chemistry, Emory and Henry College, Emory, Virginia 243272

Received 29 May 2003/ Accepted 1 September 2003

The deduced protein product of open reading frame slr0946 from Synechocystis sp. strain PCC 6803, SynArsC, contains the conserved sequence features of the enzyme superfamily that includes the low-molecular-weight protein-tyrosine phosphatases and the Staphylococcus aureus pI258 ArsC arsenate reductase. The recombinant protein product of slr0946, rSynArsC, exhibited vigorous arsenate reductase activity (Vmax = 3.1 µmol/min · mg), as well as weak phosphatase activity toward p-nitrophenyl phosphate (Vmax = 0.08 µmol/min · mg) indicative of its phosphohydrolytic ancestry. pI258 ArsC from S. aureus is the prototype of one of three distinct families of detoxifying arsenate reductases. The prototypes of the others are Acr2p from Saccharomyces cerevisiae and R773 ArsC from Escherichia coli. All three have converged upon catalytic mechanisms involving an arsenocysteine intermediate. While SynArsC is homologous to pI258 ArsC, its catalytic mechanism exhibited a unique combination of features. rSynArsC employed glutathione and glutaredoxin as the source of reducing equivalents, like Acr2p and R773 ArsC, rather than thioredoxin, as does the S. aureus enzyme. As postulated for Acr2p and R773 ArsC, rSynArsC formed a covalent complex with glutathione in an arsenate-dependent manner. rSynArsC contains three essential cysteine residues like pI258 ArsC, whereas the yeast and E. coli enzymes require only one cysteine for catalysis. As in the S. aureus enzyme, these "extra" cysteines apparently shuttle a disulfide bond to the enzyme's surface to render it accessible for reduction. SynArsC and pI258 ArsC thus appear to represent alternative branches in the evolution of their shared phosphohydrolytic ancestor into an agent of arsenic detoxification.

* Corresponding author. Mailing address: Department of Biochemistry 0308, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. Phone: (540) 231-4317. Fax: (540) 231-9070. E-mail: pjkennel{at}vt. edu.

Journal of Bacteriology, December 2003, p. 6780-6789, Vol. 185, No. 23
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.23.6780-6789.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Lopez-Maury, L., Sanchez-Riego, A. M., Reyes, J. C., Florencio, F. J. (2009). The Glutathione/Glutaredoxin System Is Essential for Arsenate Reduction in Synechocystis sp. Strain PCC 6803. J. Bacteriol. 191: 3534-3543 [Abstract] [Full Text]  
  • Li, R., Potters, M. B., Shi, L., Kennelly, P. J. (2005). The Protein Phosphatases of Synechocystis sp. Strain PCC 6803: Open Reading Frames sll1033 and sll1387 Encode Enzymes That Exhibit both Protein-Serine and Protein-Tyrosine Phosphatase Activity In Vitro. J. Bacteriol. 187: 5877-5884 [Abstract] [Full Text]  
  • Silver, S., Phung, L. T. (2005). Genes and Enzymes Involved in Bacterial Oxidation and Reduction of Inorganic Arsenic. Appl. Environ. Microbiol. 71: 599-608 [Full Text]  


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