Structural Determinants for Rubidium Binding Affinity in the Selectivity Filter of Potassium Channels

Abstract

Two competing models for potassium permeation has been proposed based on high-resolution crystallographic data, electrophysiological studies of highly K+-selective channels or mostly on computational studies. The two models are named according the way the ions interact within the channel's selectivity filter (SF). The soft knock-on model proposes the existence of two iso-energetic ion bound configurations, known as the 1-3 and 2-4 ion bound configurations. In this model, a water molecule and a K+-ion cross the cell membrane per cycle of transport and the alternate existence of the two ion bound configurations, underlies the ion selective high transport rate of potassium channels.