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A constricted opening in Kir channels does not impede potassium conduction.

Nature communications (2020-06-17)
Katrina A Black, Sitong He, Ruitao Jin, David M Miller, Jani R Bolla, Oliver B Clarke, Paul Johnson, Monique Windley, Christopher J Burns, Adam P Hill, Derek Laver, Carol V Robinson, Brian J Smith, Jacqueline M Gulbis
ABSTRACT

The canonical mechanistic model explaining potassium channel gating is of a conformational change that alternately dilates and constricts a collar-like intracellular entrance to the pore. It is based on the premise that K+ ions maintain a complete hydration shell while passing between the transmembrane cavity and cytosol, which must be accommodated. To put the canonical model to the test, we locked the conformation of a Kir K+ channel to prevent widening of the narrow collar. Unexpectedly, conduction was unimpaired in the locked channels. In parallel, we employed all-atom molecular dynamics to simulate K+ ions moving along the conduction pathway between the lower cavity and cytosol. During simulations, the constriction did not significantly widen. Instead, transient loss of some water molecules facilitated K+ permeation through the collar. The low free energy barrier to partial dehydration in the absence of conformational change indicates Kir channels are not gated by the canonical mechanism.

MATERIALS
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Sigma-Aldrich
Dibromobimane, BioReagent, suitable for fluorescence, ≥95.0% (CHN)

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