Identification of PUFA Interaction Sites on a Cardiac Potassium Channel

Abstract

Polyunsaturated fatty acids (PUFAs) have anti-arrhythmic effects in the heart, although the molecular mechanism is not fully understood. PUFAs have been shown to activate the cardiac KV7.1 channel by shifting voltage dependence of activation towards more negative voltages and increasing maximal conductance. In this study, we combine molecular dynamics simulations and electrophysiology experiments to resolve the atomistic basis for PUFA modulation of KV7.1. We find in molecular dynamics simulations that PUFAs interact with two sites on KV7.1: site 1 close to the voltage sensor in a pocket between S4 and S5 and site 2 close to the pore in a cavity between S6 and S1. The negatively-charged PUFA head group interacts with basic residues at both sites. The flexible tail of the PUFA linoleic acid allows it to form many and long-lasting interactions with hydrophobic residues in S4, S5, the pore helix, and S6. In contrast, the more rigid nature of saturated stearic acid limits its ability to form close contact with KV7.1. Mutation of several predicted binder residues from simulations were found experimentally to impair the ability of linoleic acid to activate KV7.1. Mutation of residues in site 1 primarily shifted the concentration-response for the effect on voltage dependence towards higher concentrations. Mutation of residues in site 2 primarily reduced the effect of linoleic acid on maximal conductance. Altogether, this study describes the atomistic basis of how PUFAs such as linoleic acid bind to two distinct sites in the KV7.1 channel to shift the voltage dependence of activation and increase the maximal conductance. Moreover, this study provides a mechanistic understanding of why saturated fatty acids such as stearic acid fail to activate KV7.1. The identified interactions open for development of more effective anti-arrhythmic drugs based on PUFAs.