Energy calculations for potassium vs sodium selectivity on potassium channel: an ab initio study

Numerous theoretical and experimental studies have attempted to determine the mechanisms of bacterial potassium channel selectivity (KcsA). However, there are still different aspects that remain uncovered. In this paper, we have built a model based on a selective filter (SF) for the KcsA, taking into account its structure and calculating the system interaction energy (cation-water-SF-fragment), using both sodium and potassium as cations. The results tell us which aspects could be responsible for the higher selectivity of the channel. All this reveals that there are two most important aspects: the dehydration of potassium in relation to sodium, and the environment where such dehydration occurs, in the entrance of the SF. Both semi-empirical and ab initio methods are applied to analyse and quantify the change of the interactions that take place when the cation K+ or Na+ crosses the SF.