Chen J, Sharma S, Quiocho F A, Davidson A L
Howard Hughes Medical Institute, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Proc Natl Acad Sci U S A. 2001 Feb 13;98(4):1525-30. doi: 10.1073/pnas.98.4.1525. Epub 2001 Feb 6.
High-affinity uptake into bacterial cells is mediated by a large class of periplasmic binding protein-dependent transport systems, members of the ATP-binding cassette superfamily. In the maltose transport system of Escherichia coli, the periplasmic maltose-binding protein binds its substrate maltose with high affinity and, in addition, stimulates the ATPase activity of the membrane-associated transporter when maltose is present. Vanadate inhibits maltose transport by trapping ADP in one of the two nucleotide-binding sites of the membrane transporter immediately after ATP hydrolysis, consistent with its ability to mimic the transition state of the gamma-phosphate of ATP during hydrolysis. Here we report that the maltose-binding protein becomes tightly associated with the membrane transporter in the presence of vanadate and simultaneously loses its high affinity for maltose. These results suggest a general model explaining how ATP hydrolysis is coupled to substrate transport in which a binding protein stimulates the ATPase activity of its cognate transporter by stabilizing the transition state.
细菌细胞中的高亲和力摄取是由一大类周质结合蛋白依赖性转运系统介导的，这些系统属于ATP结合盒超家族成员。在大肠杆菌的麦芽糖转运系统中，周质麦芽糖结合蛋白以高亲和力结合其底物麦芽糖，此外，当存在麦芽糖时，它会刺激膜相关转运蛋白的ATP酶活性。钒酸盐通过在ATP水解后立即将ADP捕获在膜转运蛋白的两个核苷酸结合位点之一中来抑制麦芽糖转运，这与其在水解过程中模拟ATPγ-磷酸过渡态的能力一致。我们在此报告，在钒酸盐存在下，麦芽糖结合蛋白与膜转运蛋白紧密结合，同时失去其对麦芽糖的高亲和力。这些结果提示了一个解释ATP水解如何与底物转运偶联的通用模型，其中结合蛋白通过稳定过渡态来刺激其同源转运蛋白的ATP酶活性。
