Conformational Changes in Voltage-Sensing Domains: Concerted Simulation and Scattering Studies

Abstract

Electrical signals in excitable tissues such as nerves and muscles are generated by the synchronized opening and closing of ion channels in cell membranes, which generate transient transmembrane gradients in the concentrations of sodium and potassium ions. These channels open and close in response to local changes in transmembrane potential as the signal propagates, and it is well established that their voltage sensitivity is conferred by charged structural elements, referred to as voltage-sensing domains. The details of how conformational changes in the voltage-sensing domains lead to opening/closing of the ion-conducting pores of the channels are still being worked out. Crystal structures of the open states of voltage-gated potassium channels are available, but the structure of the closed/resting state has not been determined to high resolution experimentally. In this talk I will report our efforts to generate a model of the resting state of the archaeal KvAP potassium channel based on atomistic molecular dynamics (MD) simulations in explicit membrane environments, with restraints derived from experimental functional data. I will also present results from simulation studies of an isolated voltage-sensing domain in a hydrated membrane, which include validation by neutron diffraction measurements, and direct observations of elementary gating charge displacement events during a 30-microsecond MD simulation under applied transmembrane potential. Finally, I will discuss prospects for and present preliminary results on using x-ray and neutron interferometry measurements, carried out by our collaborators, to validate and refine simulation-based models of the resting state and the voltage-sensing mechanism.