Lu T, Ting A Y, Mainland J, Jan L Y, Schultz P G, Yang J
Department of Biological Sciences, 915 Fairchild Center, MC2462, Columbia University, New York, New York 10027, USA.
Nat Neurosci. 2001 Mar;4(3):239-46. doi: 10.1038/85080.
Potassium channels selectively conduct K+ ions across cell membranes, and use diverse mechanisms to control their gating. We studied ion permeation and gating of an inwardly rectifying K+ channel by individually changing the amide carbonyls of two conserved glycines lining the selectivity filter to ester carbonyls using nonsense suppression. Surprisingly, these backbone mutations do not significantly alter ion selectivity. However, they dramatically change the kinetics of single-channel gating and produce distinct subconductance levels. The mutation at the glycine closer to the inner mouth of the pore also abolishes high-affinity binding of Ba2+ to the channel, indicating the importance of this position in ion stabilization in the selectivity filter. Our results demonstrate that K+ ion selectivity can be retained even with significant reduction of electronegativity in the selectivity filter, and that conformational changes of the filter arising from interactions between permeant ions and the backbone carbonyls contribute directly to channel gating.
钾通道可选择性地使钾离子穿过细胞膜，并利用多种机制来控制其门控。我们通过无义抑制法将位于选择性过滤器内衬的两个保守甘氨酸的酰胺羰基逐个改变为酯羰基，研究了内向整流钾通道的离子通透和门控。令人惊讶的是，这些主链突变并未显著改变离子选择性。然而，它们极大地改变了单通道门控的动力学，并产生了不同的亚电导水平。靠近孔内口的甘氨酸处的突变也消除了钡离子与通道的高亲和力结合，表明该位置在选择性过滤器中离子稳定方面的重要性。我们的结果表明，即使选择性过滤器中的电负性显著降低，钾离子选择性仍可保留，并且由通透离子与主链羰基之间的相互作用引起的过滤器构象变化直接有助于通道门控。
