Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, Porto 4150-180, Portugal.
Nature. 2013 Apr 18;496(7445):323-8. doi: 10.1038/nature12055.
In bacteria, archaea, fungi and plants the Trk, Ktr and HKT ion transporters are key components of osmotic regulation, pH homeostasis and resistance to drought and high salinity. These ion transporters are functionally diverse: they can function as Na(+) or K(+) channels and possibly as cation/K(+) symporters. They are closely related to potassium channels both at the level of the membrane protein and at the level of the cytosolic regulatory domains. Here we describe the crystal structure of a Ktr K(+) transporter, the KtrAB complex from Bacillus subtilis. The structure shows the dimeric membrane protein KtrB assembled with a cytosolic octameric KtrA ring bound to ATP, an activating ligand. A comparison between the structure of KtrAB-ATP and the structures of the isolated full-length KtrA protein with ATP or ADP reveals a ligand-dependent conformational change in the octameric ring, raising new ideas about the mechanism of activation in these transporters.
在细菌、古菌、真菌和植物中，Trk、Ktr 和 HKT 离子转运蛋白是渗透调节、pH 稳态以及耐旱和高盐抗性的关键组成部分。这些离子转运蛋白功能多样：它们可以作为 Na(+)或 K(+)通道，也可能作为阳离子/K(+)协同转运蛋白。它们在膜蛋白和胞质调节域的水平上与钾通道密切相关。在这里，我们描述了来自枯草芽孢杆菌的 Ktr K(+)转运蛋白 KtrAB 复合物的晶体结构。该结构显示了二聚体膜蛋白 KtrB 与结合了 ATP（一种激活配体）的胞质八聚体 KtrA 环组装在一起。KtrAB-ATP 的结构与具有 ATP 或 ADP 的分离全长 KtrA 蛋白的结构之间的比较揭示了八聚体环中配体依赖性的构象变化，为这些转运蛋白的激活机制提出了新的思路。
