Department of Biology, Texas A&M University, College Station, TX 77843, USA.
Nat Commun. 2013;4:2746. doi: 10.1038/ncomms3746.
Potassium (K(+)) channels are selective for K(+) over Na(+) ions during their transport across membranes. We and others have previously shown that tetrameric K(+) channels are primarily occupied by K(+) ions in their selectivity filters under physiological conditions, demonstrating the channel's intrinsic equilibrium preference for K(+) ions. Based on this observation, we hypothesize that the preference for K(+) ions over Na(+) ions in the filter determines its selectivity during ion conduction. Here, we ask whether non-selective cation channels, which share an overall structure and similar individual ion-binding sites with K(+) channels, have an ion preference at equilibrium. The variants of the non-selective Bacillus cereus NaK cation channel we examine are all selective for K(+) over Na(+) ions at equilibrium. Thus, the detailed architecture of the K(+) channel selectivity filter, and not only its equilibrium ion preference, is fundamental to the generation of selectivity during ion conduction.
钾（K(+)）通道在跨膜运输过程中对 K(+) 离子具有选择性，而对 Na(+) 离子则没有。我们和其他人之前已经表明，在生理条件下，四聚体 K(+) 通道主要被其选择性过滤器中的 K(+) 离子占据，这证明了通道对 K(+) 离子的固有平衡偏好。基于这一观察结果，我们假设过滤器中对 K(+) 离子的偏好超过 Na(+) 离子决定了其在离子传导过程中的选择性。在这里，我们想知道是否具有与 K(+) 通道总体结构和类似的单个离子结合位点的非选择性阳离子通道在平衡时具有离子偏好。我们研究的非选择性苏云金芽孢杆菌 NaK 阳离子通道的变体在平衡时均对 K(+) 离子具有选择性，而对 Na(+) 离子则没有。因此，K(+) 通道选择性过滤器的详细结构，而不仅仅是其平衡离子偏好，是在离子传导过程中产生选择性的基础。
