title: Unisite and multisite catalysis in the ArsA ATPase.
abstract: The ars operon of plasmid R773 encodes an As(III)/Sb(III) extrusion pump. The catalytic subunit, the ArsA ATPase, has two homologous halves, A1 and A2, each with a consensus nucleotide-binding sequence. ATP hydrolysis is slow in the absence of metalloid and is accelerated by metalloid binding. ArsA M446W has a single tryptophan adjacent to the A2 nucleotide-binding site. Tryptophan fluorescence increased upon addition of ATP, ADP, or a nonhydrolyzable ATP analogue. Mg(2+) and Sb(III) produced rapid quenching of fluorescence with ADP, no quenching with a nonhydrolyzable analogue, and slow quenching with ATP. The results suggest that slow quenching with ATP reflects hydrolysis of ATP to ADP in the A2 nucleotide-binding site. In an A2 nucleotide-binding site mutant, nucleotides had no effect. In contrast, in an A1 nucleotide-binding mutant, nucleotides still increased fluorescence, but there was no quenching with Mg(2+) and Sb(III). This suggests that the A2 site hydrolyzes ATP only when Sb(III) or As(III) is present and when the A1 nucleotide-binding domain is functional. These results support previous hypotheses in which only the A1 nucleotide-binding domain hydrolyzes ATP in the absence of activator (unisite catalysis), and both the A1 and A2 sites hydrolyze ATP when activated (multisite catalysis).
authors.affiliation: Department of Biochemistry and Molecular Biology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
authors.forename: Tongqing
authors.initials: T
authors.lastname: Zhou
authors.forename: Jian
authors.initials: J
authors.lastname: Shen
authors.forename: Ye
authors.initials: Y
authors.lastname: Liu
authors.forename: Barry P
authors.initials: BP
authors.lastname: Rosen
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D053501:Arsenite Transporting ATPases; D002384:Catalysis; D005453:Fluorescence; D006868:Hydrolysis; D016623:Ion Pumps / Q000737:chemistry* / Q000378:metabolism; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D016623:Ion Pumps; D009097:Multienzyme Complexes; D000255:Adenosine Triphosphate; D053501:Arsenite Transporting ATPases