Three Novel Pathways to Stabilize the Conductive Conformation of a Voltage-Gated K+ Channel

Abstract

Voltage-gated K+ channels (Kv) are tetrameric assemblies in which 4 voltage sensors open a shared K+ selective pore located at the center of the array at activating membrane potentials. A feature of many Kv channels- indispensable for the repolarization of the membrane potential following depolarization of neuronal cells- is to shut off their flux after prolonged activation. Here we show that in KvLm, a well characterized bacterial voltage-gated channel, the premature closing of the pore is bypassed by the association of the filter gate of the pore with three distinct and novel open-conformation stabilizers: A positively charged lipid, a small-molecule anti-depressant, and a protein toxin. This analysis is based on an extensive set of single channel current measurements of purified KvLm and its sensorless pore reconstituted in symmetric and asymmetric lipid bilayer membranes. Comparative assessment of the consequences produced by the three modulators in relieving the “inactivation” establishes that stabilization of the open conformation proceeds in the absence or presence of the sensors. We propose two plausible mechanisms by which all three modulators exert their demands on the pore.This work was supported by NIH grant GM 49711.