Novel insights into K+ selectivity from high-resolution structures of an open K+ channel pore.
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-A 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 K+ 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.
Ye
Sheng
S
Life Sciences Institute, Zhejiang University, Zhejiang, China. sye@zju.edu.cn
Li
Yang
Y
Jiang
Youxing
Y
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D015640:Ion Channel Gating / Q000187:drug effects; D007477:Ions; D017014:Methanobacterium / Q000737:chemistry*; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D055672:Static Electricity; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; D007477:Ions; D015221:Potassium Channels; D011188:Potassium