Elucidation of Molecular Mechanism Underlying KcsA's Hysteretic Gating Behavior

Abstract

Hysteresis has been observed in cyclic nucleotide-gated4, transient receptor potential vanilloid3, N-methyl-D-aspartate5, human Ether-a-go-go-Related Gene6, human HCN48, mouse HCN11 channels. Voltage shift for QV (gating charge vs voltage) curve is well documented for voltage-gated cation channels, which was considered an intrinsic property of the voltage-sensing domain (VSD). However, it was showed recently that uncoupling the VSD from the pore domain of the Shaker K+ channel, eliminated the VSD's hysteretic gating behavior. It was suggested that the pore domain imposes a mechanical load on the VSD due to stabilization of an open state, which causes the hysteresis2. Since open-state stabilization occur at the channels’ pore domain, it is important to study the pore domain gating mechanism in isolation. We intend to use the archetypal pore domain of a K+ channel, KcsA, as a functional and structural surrogate, to elucidate the molecular basis of hysteretic gating behavior in ion channels. Recently, we have unveiled a novel hysteretic gating behavior in KcsA by electrophysiology and by continuous wave electron paramagnetic resonance spectroscopy, which faithfully measure the pH dependent conformational changes associated to activation7 and deactivation gating. We hypothesize that structural changes of the KcsA's selectivity filter associated to C-type inactivation underlie the molecular mechanism of hysteretic gating in KcsA and by extension in other ion channels. The long-term goal of this project is to determine the molecular basis for hysteretic gating in ion channels, which can be useful for the development of drugs that can correct several channelopathies.