title: Motifs Q and I are required for ATP hydrolysis but not for ATP binding in SWI2/SNF2 proteins.
abstract: Active DNA-dependent ATPase A Domain (ADAAD) is a SWI2/SNF2 protein that hydrolyzes ATP in the presence of stem-loop DNA that contains both double-stranded and single-stranded regions. ADAAD possesses the seven helicase motifs that are a characteristic feature of all the SWI2/SNF2 proteins present in yeast as well as mammalian cells. In addition, these proteins also possess the Q motif ~17 nucleotides upstream of motif I. Using site-directed mutagenesis, we have sought to define the role of motifs Q and I in ATP hydrolysis mediated by ADAAD. We show that in ADAAD both motifs Q and I are required for ATP catalysis but not for ATP binding. In addition, the conserved glutamine present in motif Q also dictates the catalytic rate. The ability of the conserved glutamine present in motif Q to dictate the catalytic rate has not been observed in helicases. Further, the SWI2/SNF2 proteins contain a conserved glutamine, one amino acid residue downstream of motif I. This conserved glutamine, Q244 in ADAAD, also directs the rate of catalysis but is not required either for hydrolysis or for ligand binding. Finally, we show that the adenine moiety of ATP is sufficient for interaction with SWI2/SNF2 proteins. The γ-phosphate of ATP is required for inducing the conformational change that leads to ATPase activity. Thus, the SWI2/SNF2 proteins despite sequence conservation with helicases appear to behave in a manner distinct from that of the helicases.
authors.affiliation: School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India.
authors.forename: Macmillan
authors.initials: M
authors.lastname: Nongkhlaw
authors.forename: Meghna
authors.initials: M
authors.lastname: Gupta
authors.forename: Sneha Sudha
authors.initials: SS
authors.lastname: Komath
authors.forename: Rohini
authors.initials: R
authors.lastname: Muthuswami
mesh_terms: D000225:Adenine / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D020816:Amino Acid Motifs; D000818:Animals; D002384:Catalysis; D002417:Cattle; D053487:DEAD-box RNA Helicases / Q000737:chemistry / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004265:DNA Helicases / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry; D048229:Sulfolobus solfataricus / Q000201:enzymology
chemical_list: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D004247:DNA; D004265:DNA Helicases; D053487:DEAD-box RNA Helicases; D008274:Magnesium; D000225:Adenine