Albright Ronald A, Ibar José-Luís Vazquez, Kim Chae Un, Gruner Sol M, Morais-Cabral João Henrique
Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT 06520, USA.
Cell. 2006 Sep 22;126(6):1147-59. doi: 10.1016/j.cell.2006.08.028.
The KtrAB ion transporter is a complex of the KtrB membrane protein and KtrA, an RCK domain. RCK domains regulate eukaryotic and prokaryotic membrane proteins involved in K(+) transport. Conflicting functional models have proposed two different oligomeric arrangements for RCK domains, tetramer versus octamer. Our results for the KtrAB RCK domain clearly show an octamer in solution and in the crystal. We determined the structure of this protein in three different octameric ring conformations that resemble the RCK-domain octamer observed in the MthK potassium channel but show striking differences in size and symmetry. We present experimental evidence for the association between one RCK octameric ring and two KtrB membrane proteins. These results provide insights into the quaternary organization of the KtrAB transporter and its mechanism of activation and show that the RCK-domain octameric ring model is generally applicable to other ion-transport systems.
KtrAB离子转运体是由KtrB膜蛋白和KtrA（一个RCK结构域）组成的复合物。RCK结构域调控参与钾离子转运的真核和原核膜蛋白。相互矛盾的功能模型针对RCK结构域提出了两种不同的寡聚体排列方式，即四聚体与八聚体。我们对KtrAB RCK结构域的研究结果清楚地表明，在溶液和晶体中它均为八聚体。我们确定了该蛋白在三种不同八聚体环构象中的结构，这些构象类似于在MthK钾通道中观察到的RCK结构域八聚体，但在大小和对称性上存在显著差异。我们提供了一个RCK八聚体环与两个KtrB膜蛋白之间关联的实验证据。这些结果为KtrAB转运体的四级结构组织及其激活机制提供了见解，并表明RCK结构域八聚体环模型通常适用于其他离子转运系统。
