Structure of the Pore Module of a Voltage-Gated Channel in a Lipid Environment at 3.1 Å Resolution

Abstract

KvLm is a voltage-gated K+-selective channel encoded in the genome of Listeria monocytogenes. The expression and reconstitution of the isolated pore module (KvLm-PM) has shown that, in the absence of the sensor, the pore module gates with low but measurable voltage-dependence and remains highly selective for K+. Here we present the first structure of an ion conducting channel crystallized in the lipid cubic phase (LCP) at 3.1 A resolution. The structure of the tetramer depicts a filter gate in a conductive conformation but with decreased ion occupancy and an activation gate closed both sterically and electrostatically. Comparison with other K+ channel structures in which the activation gate is closed highlights for KvLm-PM a permeation path between the filter and the activation gate that is significantly narrower and shorter. The lipid environment results in the immobilization of four lipid molecules per monomer all clustered in a crevice between subunits at the cytoplasmic face of the pore. The position of these lipid molecules overlaps with those found in other K+-selective channel structures consistent with the presence of a conserved lipid immobilization site. Reconstitution of KvLm-PM in lipid bilayers that mimic the crystallization condition shows that the channel exhibits the full complement of functional properties.This work was supported by grants from the National Institutes of Health (Road Map Joint Center for Innovative Membrane Protein Technologies and GM49711).