The potassium channel: Structure, selectivity and diffusion

We employ the entire experimentally determined protein structure for the KcsA potassium channel from Streptomyces lividans in molecular dynamics calculations to observe hydrated channel protein structure, ion solvation, selectivity, multiple ion configurations, and diffusion. Free energy perturbation calculations display a significant ion discrimination of ∼9 kT in favor of the larger K⁺ ion. The protein forming the channel is very flexible yet is unable to fully solvate the Na⁺ ion because of its smaller size and large solvation energy. There is evidence that acidic and basic sidechains may dissociate in the presence of multiple K⁺ ions to explain experimental ion density maps. K⁺ diffusion is found to vary from approximately 10%-90% of bulk, supporting the high channel currents observed experimentally.