Conformational equilibrium shift underlies altered K(+) channel gating as revealed by NMR

The potassium ion (K(+)) channel plays a fundamental role in controlling K(+) permeation across the cell membrane and regulating cellular excitabilities. Mutations in the transmembrane pore reportedly affect the gating transitions of K(+) channels, and are associated with the onset of neural disorders. However, due to the lack of structural and dynamic insights into the functions of K(+) channels, the structural mechanism by which these mutations cause K(+) channel dysfunctions remains elusive. Here, we used nuclear magnetic resonance spectroscopy to investigate the structural mechanism underlying the decreased K(+)-permeation caused by disease-related mutations, using the prokaryotic K(+) channel KcsA. We demonstrated that the conformational equilibrium in the transmembrane region is shifted toward the non-conductive state with the closed intracellular K(+)-gate in the disease-related mutant. We also demonstrated that this equilibrium shift is attributable to the additional steric contacts in the open-conductive structure, which are evoked by the increased side-chain bulkiness of the residues lining the transmembrane helix. Our results suggest that the alteration in the conformational equilibrium of the intracellular K(+)-gate is one of the fundamental mechanisms underlying the dysfunctions of K(+) channels caused by disease-related mutations.