Nat Struct Mol Biol. 2010 Aug;17(8):1019-23.

Sheng Ye*, Yang Li, Youxing Jiang*

Abstract

K⁺channels are highly selective for K⁺ over Na⁺. Here we present several crystal structures of the MthK K⁺ channel pore at up to 1.45-Å resolution. The MthK selectivity filter maintains a conductive conformation even in the absence of K⁺, allowing the channel to conduct Na⁺. The high-resolution structures, along with single-channel recordings, allow for an accurate analysis of how K⁺ competes with Na+ in a conductive selectivity filter. At high K⁺concentrations, two Kv ions equivalently occupy the four sites in the selectivity filter, whereas at low K⁺/high Na⁺ concentrations, a single K⁺ ion remains bound in the selectivity filter, preferably at site 1 or site 3. This single K⁺ binding at low concentration effectively blocks the permeation of Na⁺, providing a structural basis for the anomalous mole-fraction effect, a key property of multi-ion pores.

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