Glutathione-S-transferase from the arsenic hyperaccumulator fern Pteris vittata can confer increased arsenate resistance in Escherichia coli

Abstract

Although arsenic is generally a toxic compound, there are a number of ferns in the genus Pteris that can tolerate large concentrations of this metalloid. In order to probe the mechanisms of arsenic hyperaccumulation, we expressed a Pteris vittata cDNA library in an Escherichia coli {Delta}arsC (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 the P. vittata GSTs in E. coli was abrogated by a gshA mutation, which blocks the synthesis of glutathione, and by a gor mutation, which inactivates glutathione reductase. Direct measurements of the speciation of arsenic in culture media of the E. coli strains expressing the P. vittata GSTs indicated that these proteins facilitate the reduction of arsenate. Our observations suggest that the detoxification of arsenate by the P. vittata GSTs involves reduction of As(V) to As(III) by glutathione or a related sulfhydro compound.\n\nFundingThe 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.