Identification of PUFA interaction sites on the cardiac potassium channel KCNQ1.

Samira Yazdi,Sergei Yu Noskov,H Peter Larsson,Sara I Liin,D Peter Tieleman,Valentina Corradi,Williams Miranda,Johan Nikesjö

doi:10.1085/jgp.202012850

Samira Yazdi, Sergei Yu Noskov + Show 6 more

Open Access

https://doi.org/10.1085/jgp.202012850

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Abstract

Polyunsaturated fatty acids (PUFAs), but not saturated fatty acids, modulate ion channels such as the cardiac KCNQ1 channel, although the mechanism is not completely understood. Using both simulations and experiments, we find that PUFAs interact directly with the KCNQ1 channel via two different binding sites: one at the voltage sensor and one at the pore. These two amphiphilic binding pockets stabilize the negatively charged PUFA head group by electrostatic interactions with R218, R221, and K316, while the hydrophobic PUFA tail is selectively stabilized by cassettes of hydrophobic residues. The rigid saturated tail of stearic acid prevents close contacts with KCNQ1. By contrast, the mobile tail of PUFA linoleic acid can be accommodated in the crevice of the hydrophobic cassette, a defining feature of PUFA selectivity in KCNQ1. In addition, we identify Y268 as a critical PUFA anchor point underlying fatty acid selectivity. Combined, this study provides molecular models of direct interactions between PUFAs and KCNQ1 and identifies selectivity mechanisms. Long term, this understanding may open new avenues for drug development based on PUFA mechanisms.

Highlights

We studied the interaction of the ω6 Polyunsaturated fatty acids (PUFAs) linoleic acid (LIN) or saturated fatty acids (FAs) STE with the KCNQ1 channel by combining long-time-scale CG MD and microseconds-long AA MD simulations in a multicomponent membrane bilayer with a lipid composition of POPE, POPG, CHOL, and PIP2 and PUFAs added to both leaflets
Based on our previous experimental findings that residues in the extracellular part of the channel are important for PUFA activation of the KCNQ1 channel (Liin et al, 2015; Larsson et al, 2018; Liin et al, 2018), we focused our analysis on PUFA–channel interactions in the outer leaflet of the lipid bilayer
We discovered a novel head group interaction—a hydrogen bond between Y268 and the negative PUFA head group—with KCNQ1 at the voltage sensor site

Summary

Introduction

Polyunsaturated fatty acids (PUFAs) affect many different ion channels, such as voltage-gated K+, Na+, and Ca2+ channels, as well as ryanodine receptors (Xiao et al, 2001; Hamilton et al, 2003; Oliver et al, 2004; Xiao et al, 2005; Ottosson et al, 2014; Farag et al, 2016; Tian et al, 2016; Liin et al, 2018; Bohannon et al, 2020). The identity of PUFAs’ specific binding pockets remains uncharacterized for many ion channels; the molecular mechanisms of PUFA efficacy are still poorly understood. We previously showed that PUFAs act as activators of KCNQ1 (Liin et al, 2015), which is expressed, for instance, in cardiomyocytes (forming the KCNQ1/KCNE1 channel) and smooth muscle cells (Barrese et al, 2018). KCNQ1 forms a tetrameric, voltage-gated potassium channel with six transmembrane segments (S1–S6) in each subunit (Sun and MacKinnon, 2017). Helices S1–S4 in each subunit form a voltage-sensing domain with positively charged arginine residues in S4 acting as the voltage sensor. S5–S6 from all four subunits together form the centrally located pore domain with the potassium selectivity filter and activation gate. Outward movement of the positively charged S4 in response to depolarization triggers opening of the activation gate and allows for the outward flux of potassium (Osteen et al, 2012; Barro-Soria et al, 2014; Zaydman et al, 2014; Hou et al, 2017; Westhoff et al, 2019)

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