Lysenin Channel Selectivity for Monovalent Metal Cations

The ability of transmembranes to selectively transport ions and molecules across biological membranes is paramount for all cells. The functionality of excitable cells, such as the excitability from the brain and muscles, is unequivocally determined by the ability of ion channels to discriminate between ionic solutes. Selectivity, along with high transport rate and regulation, is fundamental for all ion channels. Following this line of thinking, we asked whether other protein channels, with regulatory functions, have similar selectivity to ion channels. Our investigations were focused on lysenin, a protein that self-assembles into a regulated, large-conductance channel in both artificial and natural lipid membranes. The ionic selectivity of lysenin channels of monovalent metal cations was estimated through transmembrane voltages measured after chemical gradients were produced across the membrane through successive ionic additions. Our results clearly demonstrated that lysenin channels present cation selectivity. However, the estimated ionic permeabilities were different for Na+, K+, Li+, and Cs+. This unusual feature, commonly shared by ion channels, may be further explored for controlling the electrochemical gradients across natural and artificial cell membranes.