Walmsley A R, Zhou T, Borges-Walmsley M I, Rosen B P
Division of Infection and Immunity, the Institute of Biomedical and Life Sciences, Robertson Building, The University of Glasgow, Glasgow G11 6NU, Scotland, United Kingdom.
J Biol Chem. 2001 Mar 2;276(9):6378-91. doi: 10.1074/jbc.M008105200. Epub 2000 Nov 28.
ArsA is the catalytic subunit of the arsenical pump, coupling ATP hydrolysis to the efflux of arsenicals through the ArsB membrane protein. It is a paradigm for understanding the structure-function of the nucleotide binding domains (NBD) of medically important efflux pumps, such as P-glycoprotein, because it has two sequence-related, interacting NBD, for which the structure is known. On the basis of a rigorous analysis of the pre-steady-state kinetics of nucleotide binding and hydrolysis, we propose a model in which ArsA alternates between two mutually exclusive conformations as follows: the ArsA(1) conformation in which the A1 site is closed but the A2 site open; and the ArsA(2) conformation, in which the A1 and A2 sites are open and closed, respectively. Antimonite elicits its effects by sequestering ArsA in the ArsA(1) conformation, which catalyzes rapid ATP hydrolysis at the A2 site to drive ArsA between conformations that have high (nucleotide-bound ArsA) and low affinity (nucleotide-free ArsA) for Sb(III). ArsA potentially utilizes this process to sequester Sb(III) from the medium and eject it into the channel of ArsB.
ArsA是砷泵的催化亚基，它将ATP水解与砷通过ArsB膜蛋白的外排相偶联。它是理解医学上重要的外排泵（如P-糖蛋白）核苷酸结合结构域（NBD）结构与功能的范例，因为它有两个序列相关且相互作用的NBD，其结构是已知的。基于对核苷酸结合和水解的预稳态动力学的严格分析，我们提出了一个模型，其中ArsA在两种互斥构象之间交替如下：ArsA(1)构象，其中A1位点关闭但A2位点开放；以及ArsA(2)构象，其中A1和A2位点分别开放和关闭。亚锑酸盐通过将ArsA隔离在ArsA(1)构象中来发挥其作用，该构象催化A2位点的快速ATP水解，以驱动ArsA在对Sb(III)具有高亲和力（核苷酸结合的ArsA）和低亲和力（无核苷酸的ArsA）的构象之间转换。ArsA可能利用这个过程从培养基中隔离Sb(III)并将其排入ArsB的通道。
