Ogawa Haruo, Shinoda Takehiro, Cornelius Flemming, Toyoshima Chikashi
Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
Proc Natl Acad Sci U S A. 2009 Aug 18;106(33):13742-7. doi: 10.1073/pnas.0907054106. Epub 2009 Aug 3.
The sodium-potassium pump (Na(+),K(+)-ATPase) is responsible for establishing Na(+) and K(+) concentration gradients across the plasma membrane and therefore plays an essential role in, for instance, generating action potentials. Cardiac glycosides, prescribed for congestive heart failure for more than 2 centuries, are efficient inhibitors of this ATPase. Here we describe a crystal structure of Na(+),K(+)-ATPase with bound ouabain, a representative cardiac glycoside, at 2.8 A resolution in a state analogous to E2.2K(+).Pi. Ouabain is deeply inserted into the transmembrane domain with the lactone ring very close to the bound K(+), in marked contrast to previous models. Due to antagonism between ouabain and K(+), the structure represents a low-affinity ouabain-bound state. Yet, most of the mutagenesis data obtained with the high-affinity state are readily explained by the present crystal structure, indicating that the binding site for ouabain is essentially the same. According to a homology model for the high affinity state, it is a closure of the binding cavity that confers a high affinity.
钠钾泵（Na⁺，K⁺-ATP酶）负责在质膜上建立Na⁺和K⁺浓度梯度，因此在诸如产生动作电位等过程中发挥着至关重要的作用。两个多世纪以来一直用于治疗充血性心力衰竭的强心苷是这种ATP酶的有效抑制剂。在此，我们描述了与代表性强心苷哇巴因结合的Na⁺，K⁺-ATP酶的晶体结构，其分辨率为2.8 Å，处于类似于E2·2K⁺·Pi的状态。与之前的模型形成鲜明对比的是，哇巴因深深插入跨膜结构域，内酯环非常靠近结合的K⁺。由于哇巴因和K⁺之间的拮抗作用，该结构代表了一种低亲和力的哇巴因结合状态。然而，目前的晶体结构很容易解释大多数在高亲和力状态下获得的诱变数据，这表明哇巴因的结合位点基本相同。根据高亲和力状态的同源模型，结合腔的闭合赋予了高亲和力。
