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Journal of Bacteriology, June 2009, p. 3534-3543, Vol. 191, No. 11
0021-9193/09/$08.00+0     doi:10.1128/JB.01798-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Glutathione/Glutaredoxin System Is Essential for Arsenate Reduction in Synechocystis sp. Strain PCC 6803{triangledown} ,{dagger}

Luis López-Maury,{ddagger} Ana María Sánchez-Riego, José Carlos Reyes,§ and Francisco J. Florencio*

Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC—Universidad de Sevilla, Américo Vespucio 49, E-41092 Seville, Spain

Received 22 December 2008/ Accepted 13 March 2009

Arsenic resistance in Synechocystis sp. strain PCC 6803 is mediated by an operon of three genes in which arsC codes for an arsenate reductase with unique characteristics. Here we describe the identification of two additional and nearly identical genes coding for arsenate reductases in Synechocystis sp. strain PCC 6803, which we have designed arsI1 and arsI2, and the biochemical characterization of both ArsC (arsenate reductase) and ArsI. Functional analysis of single, double, and triple mutants shows that both ArsI enzymes are active arsenate reductases but that their roles in arsenate resistance are essential only in the absence of ArsC. Based on its biochemical properties, ArsC belongs to a family that, though related to thioredoxin-dependent arsenate reductases, uses the glutathione/glutaredoxin system for reduction, whereas ArsI belongs to the previously known glutaredoxin-dependent family. We have also analyzed the role in arsenate resistance of the three glutaredoxins present in Synechocystis sp. strain PCC 6803 both in vitro and in vivo. Only the dithiolic glutaredoxins, GrxA (glutaredoxin A) and GrxB (glutaredoxin B), are able to donate electrons to both types of reductases in vitro, while GrxC (glutaredoxin C), a monothiolic glutaredoxin, is unable to donate electrons to either type. Analysis of glutaredoxin mutant strains revealed that only those lacking the grxA gene have impaired arsenic resistance.

* Corresponding author. Mailing address: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla—CSIC, Av. Americo Vespucio 49, E 41092 Seville, Spain. Phone: 34 954489509. Fax: 34 954460065. E-mail: floren{at}us.es

{triangledown} Published ahead of print on 20 March 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Fission Yeast Functional Genomics, Cancer Research UK, Wellcome Trust Sanger Institute, Morgan Building, Hinxton, Cambridge CB10 1HH, United Kingdom.

§ Present address: Centro Andaluz de Biología Molecular y Medicina Regenerativa, Consejo Superior de Investigaciones Científicas, Av. Américo Vespucio s/n, 41092 Seville, Spain.

Journal of Bacteriology, June 2009, p. 3534-3543, Vol. 191, No. 11
0021-9193/09/$08.00+0     doi:10.1128/JB.01798-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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