Crystal structure of the potassium-importing KdpFABC membrane complex.
Crystal structure of the potassium-importing KdpFABC membrane complex.
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DOI：
10.1038/nature22970
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发表时间：
2017-06-29
期刊：
影响因子：
64.8
通讯作者：
Stokes DL
中科院分区：
文献类型：
--
作者：
Huang CS;Pedersen BP;Stokes DL
细胞钾输入系统在生命各个领域的渗透调节、pH动态平衡和膜电位中起着重要的作用。在细菌中，KDP操纵子编码一个四个亚单位的钾泵，在钾有限的条件下维持细胞内的动态平衡以及细胞的形状和膨胀。这个膜复合体被称为KdpFABC，它有一个通道样亚单位(KdpA)属于钾转运体超家族，另一个泵样亚单位(KdpB)属于P型ATPase超家族。虽然关于这两个超家族成员的结构和功能信息很多，但KdpA的上行钾转运和KdpB对ATP的水解机制仍然知之甚少。本文报道了完整的大肠杆菌KdpFABC与KdpA选择性滤膜内的钾离子以及KdpB跨膜区中正离子位置的水分子形成的完整的KdpFABC络合物的2.9？X-射线结构。该结构还揭示了两个结构元素，它们似乎调节了这两个亚单位之间的耦合。具体地说，在这些钾和水之间有一条蛋白质嵌入的隧道，控制KdpA的细胞质门的螺旋连接到KdpB的磷酸化结构域。基于这些观察，我们提出了一种史无前例的机制，重新定位蛋白质通道结构以通过生物膜进行主动运输。
Cellular potassium import systems play a fundamental role in osmoregulation, pH homeostasis and membrane potential in all domains of life. In bacteria, the kdp operon encodes a four subunit potassium pump that maintains intracellular homeostasis as well as cell shape and turgor under conditions where potassium is limiting. This membrane complex, called KdpFABC, has one channel-like subunit (KdpA) belonging to the Superfamily of Potassium Transporters and another pump-like subunit (KdpB) belonging to the Superfamily of P-type ATPases. Although there is considerable structural and functional information about members from both superfamilies, the mechanism by which uphill potassium transport through KdpA is coupled with ATP hydrolysis by KdpB remains poorly understood. Here we report the 2.9 Å X-ray structure of the complete Escherichia coli KdpFABC complex with a potassium ion within the selectivity filter of KdpA as well as a water molecule at a canonical cation site in the transmembrane domain of KdpB. The structure also reveals two structural elements that appear to mediate the coupling between these two subunits. Specifically, a protein-embedded tunnel runs between these potassium and water sites and a helix controlling the cytoplasmic gate of KdpA is linked to the phosphorylation domain of KdpB. Based on these observations, we propose an unprecedented mechanism that repurposes protein channel architecture for active transport across biomembranes.