title: Is ATP binding responsible for initiating drug translocation by the multidrug transporter ABCG2?
abstract: ABCG2 confers resistance to cancer cells by mediating the ATP-dependent outward efflux of chemotherapeutic compounds. Recent studies have indicated that the protein contains a number of interconnected drug binding sites. The present investigation examines the coupling of drug binding to ATP hydrolysis. Initial drug binding to the protein requires a high-affinity interaction with the drug binding site, followed by transition and reorientation to the low-affinity state to enable dissociation at the extracellular face. [3H]Daunomycin binding to the ABCG2 R482G isoform was examined in the nucleotide-bound and post-hydrolytic conformations. Binding of [3H]daunomycin was displaced by ATP analogues, indicating transition to a low-affinity conformation prior to hydrolysis. The low-affinity state was observed to be retained immediately post-hydrolysis. Therefore, the dissociation of phosphate and/or ADP is likely to be responsible for resetting of the transporter. The data indicate that, like ABCB1 and ABCC1, the 'power stroke' for translocation in ABCG2 R482G is the binding of nucleotide.
authors.affiliation: Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, University of Oxford, UK.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: McDevitt
authors.forename: Emily
authors.initials: E
authors.lastname: Crowley
authors.forename: Gemma
authors.initials: G
authors.lastname: Hobbs
authors.forename: Kate J
authors.initials: KJ
authors.lastname: Starr
authors.forename: Ian D
authors.initials: ID
authors.lastname: Kerr
authors.forename: Richard
authors.initials: R
authors.lastname: Callaghan
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism* / Q000493:pharmacokinetics; D002460:Cell Line; D003630:Daunorubicin / Q000378:metabolism* / Q000493:pharmacokinetics; D009036:Moths; D009363:Neoplasm Proteins / Q000502:physiology*; D011485:Protein Binding; D011869:Radioligand Assay; D014316:Tritium
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D009363:Neoplasm Proteins; D014316:Tritium; D000255:Adenosine Triphosphate; D003630:Daunorubicin