Oriented Circular Dichroism Spectroscopy as a Tool for Studying the Gating of Sodium Channels

Abstract

Voltage Gated Sodium Channels (Navs) are important pharmacological targets as the sight of action for local anaesthetics, anti-arrhythmic and anticonvulsants. While drugs may be used to individually target conditions they have little specificity for the subtypes of different tissues, this is explained by a state-dependant binding. The Nav from Magnetococcus marinus, NavMs, has proven to be a useful model for studying eukaryotic Navs, sharing both homology and relevant pharmacology; furthermore, it can be obtained with a yield and purity required for structural and biophysical studies. While the binding of ligands to both eukaryotic and Navs has been inferred by electrophysiology there is little information on the state or conformation of drug-bound channels. We are developing Oriented Synchrotron Radiation Circular Dichroism (oSRCD) spectroscopy as a method for examining the conformational changes of NavMs that occur upon ligand binding. The spectra of oriented samples of helical membrane proteins are dependent upon the angle the transmembrane helices make relative to the incident light beam. Monitoring changes in their spectra can inform on angular changes of the pore lining helices associated with channel gating as a result of external stimuli such as ligand binding.