Insights into the Ion Permeation Process of High and Low Conductance K-Channels using Non-Equilibrium Molecular Dynamics

Abstract

Potassium channels are membrane proteins that allow fast and selective flow of K+ ions across membranes, participating on the regulation of the electrical properties of the cell, generation and propagation of electrical impulses in nervous systems, gene expression regulation, neurotransmitters release. K+ channels have a selectivity filter (SF) composed by a highly conserved sequence TVGYGD, which forms the narrowest part of the channel. Despite the fact that the structure of the SF is conserved among K+ channels, they show different conductance rates e.g. 250 pS for BK channel and 20 pS for Shaker channel. Moreover, a single mutation in Shaker (P475D) can increase its conductance from 20 pS to 180 pS.Molecular dynamics simulations of the aforementioned K+ channels were performed in order to describe the molecular properties that modulate the conductance process. To analyze these properties an external electric fields were applied, allowing a faster permeation of K+ ions and therefore to have a further approximation of the patch clamp experimental conditions.Using this non-equilibrium approach a number of outward K+ transport events were observed in a high and low conductance K+ channels. The properties involved in the K+ ion conductance process were characterized at molecular level through computing the electrostatic potentials profile, PMF (ABF method) profiles, permeation events number, K+ desolvation process and K+ ion density inside the pore. This study provides new perspectives to understand the ion conductance observed in high and low conductance K+ channels, allowing to propose new hypotheses which were validated through site directed mutagenesis and electrophysiological assays.Acknowledgement: This work was supported by FONDECYT 1131003 (FGN), 1120818 (DN) and CINV (Millenium Initiative, 09-022-F), RS thanks to CONICYT for doctoral scholarship.