Molecular characterization of an anion pump. The arsA gene product is an arsenite(antimonate)-stimulated ATPase

Abstract

The products of the arsenical resistance operon of resistance plasmid R733 form an efflux system for arsenicals. Detoxification results from active efflux of the oxyanions, preventing their concentration from reaching toxic levels. The largest polypeptide encoded by the ars operon was purified. From N-terminal sequencing the purified protein, termed the ArsA protein, was shown to correspond to the product of the arsA gene. The purified protein was demonstrated to bind ATP by two methods. First, a photoadduct of the protein with [alpha-32P]ATP was formed by irradiation at 254 nm. Second, the purified protein bound a fluorescent ATP analogue, 2',3'-o-(2,4,6)trinitrophenyl ATP, with a half-maximal affinity of 2 microM. By both assays competition was observed with ATP or ADP, but not with AMP, GTP, CTP, or UTP. In both nucleotide binding assays, Mg2+ was required, but neither arsenite nor antimonate had any affect. In contrast, the ArsA protein exhibited an ATPase activity which was dependent on the presence of arsenite or antimonate. The results suggest that the ArsA protein is the catalytic subunit of an oxyanion-translocating ATPase.