Glutathione-S-transferase from the arsenic hyperaccumulator fernPteris vittatacan confer increased arsenate resistance inEscherichia coli

Although arsenic is generally a toxic compound, there are a number of ferns in the genusPteristhat can tolerate large concentrations of this metalloid. In order to probe the mechanisms of arsenic hyperaccumulation, we expressed aPteris vittatacDNA library in anEscherichia coli ΔarsC(arsenate reductase) mutant. We obtained three independent clones that conferred increased arsenate resistance on this host. DNA sequence analysis indicated that these clones specify proteins that have a high sequence similarity to the phi class of glutathione-S-transferases (GSTs) of higher plants. Detoxification of arsenate by theP. vittataGSTs inE. coliwas abrogated by agshAmutation, which blocks the synthesis of glutathione, and by agormutation, which inactivates glutathione reductase. Direct measurements of the speciation of arsenic in culture media of theE. colistrains expressing theP. vittataGSTs indicated that these proteins facilitate the reduction of arsenate. Our observations suggest that the detoxification of arsenate by theP. vittataGSTs involves reduction of As(V) to As(III) by glutathione or a related sulfhydro compound.FundingThe authors acknowledge support from the Indiana 21st Century Research and technology Fund (912010479) to DES and LNC, from the U.S. Department of Energy (grant no. DE-FG02-03ER63622) to DES, and from BBSRC-DFID (grant no. BBF0041841GJN) to AAM. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. There are no financial, personal, or professional interests that could be construed to have influenced the paper.