Molecular Interactions Involved in KCSA pH Gating

Abstract

The bacterial potassium channel KcsA is gated by high concentrations of intracellular protons, allowing the channel to open at pH < 5.5. Replacing key ionizable residues from the N and C termini of KcsA with residues mimicking their protonated counterparts with respect to charge renders the channel open up to pH 9.0 (Thompson et al. 2008). We proposed that these residues function as the proton-binding sites. At neutral pH they form a complex network of inter- and intrasubunit salt bridges and hydrogen bonds near the bundle crossing, stabilizing the closed state. At acidic pH, these residues change their ionization state, thereby disrupting this network, favoring channel opening. While our previous work identified a network of residues involved in pH sensing, it did not rigorsously dissect the interactions that govern channel opening. To this end, we performed a series of single and pairwise mutations of the residues in the pH sensor. Using electrophysiology and X-ray crystallography we hope to gain a deeper insight into the mechanism of proton dependent gating in KcsA.