McDevitt Christopher A, Crowley Emily, Hobbs Gemma, Starr Kate J, Kerr Ian D, Callaghan Richard
Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, University of Oxford, UK.
FEBS J. 2008 Sep;275(17):4354-62. doi: 10.1111/j.1742-4658.2008.06578.x. Epub 2008 Jul 24.
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.
ABCG2 通过介导化疗化合物的 ATP 依赖性外向流出赋予癌细胞耐药性。最近的研究表明，该蛋白包含多个相互连接的药物结合位点。本研究考察了药物结合与 ATP 水解的偶联。药物与蛋白的初始结合需要与药物结合位点进行高亲和力相互作用，随后转变并重新定向至低亲和力状态，以便在细胞外表面解离。在核苷酸结合构象和水解后构象中检测了 [3H]柔红霉素与 ABCG2 R482G 异构体的结合。ATP 类似物可取代 [3H]柔红霉素的结合，表明在水解之前转变为低亲和力构象。观察到在水解后立即保留低亲和力状态。因此，磷酸盐和/或 ADP 的解离可能负责转运体的重置。数据表明，与 ABCB1 和 ABCC1 一样，ABCG2 R482G 转运的“动力冲程”是核苷酸的结合。
