Asynchronous motion and transport of K+ in the KcsA selectivity filter

A recently proposed Markovian model of K+ ion transport through the selectivity filter of the KcsA bacterial channel is generalized. This generalization allows a specific estimate to be made of the current through the channel which is found to be consistent with experimentally determined values [11.0 (+/−) 0.1 pA]. A further aspect of the generalization presented here is the quantification of the difference of synchronous vs. asynchronous motion of the K+ ions and water molecules in the channel. Considering excluded volume effects only, the difference in mean passage time through the channel is in the range 50%-75%; on the basis of calculations reported here, we argue that this difference will be even more pronounced when K+/ K+ Coulombic repulsions and electrostatic attractive interactions between K+ ions and the carbonyl groups lining the channel are taken into account.