The voltage-dependence of MscL has dipolar and dielectric contributions and is governed by local intramembrane electric field

Joseph S Najem,Sergei Sukharev,Andriy Anishkin,Donald J Leo,Ian Rowe

doi:10.1038/s41598-018-31945-x

Abstract

Channels without canonical voltage sensors can be modulated by voltage acting on other domains. Here we show that besides protein dipoles, pore hydration can be affected by electric fields. In patches, both WT MscL and its V23T mutant show a decrease in the tension midpoint with hyperpolarization. The mutant exhibits a stronger parabolic dependence of transition energy on voltage, highly consistent with the favourable dielectric contribution from water filling the expanding pore. Purified V23T MscL in DPhPC droplet interface bilayers shows a similar voltage dependence. When reconstituted in an asymmetric DOPhPC/DPhPC bilayer carrying a permanent bias of ~130 mV due to a dipole potential difference between the interfaces, the channel behaved as if the local intramembrane electric field sets the tension threshold for gating rather than just the externally applied voltage. The data emphasize the roles of polarized water in the pore and interfacial lipid dipoles in channel gating thermodynamics.

Highlights

Transmembrane voltage is a critical parameter for most ion channels because (i) it provides the driving force for ions and (ii) it is a powerful factor in triggering and modulating channel gating
The data obtained in DIBs confirm that V23T MscL senses the local intramembrane electric field in the membrane core between the interfacial layers, and the voltage imposed by external electrodes is sensed not directly, but rather in combination with the potential imparted by the lipids
For WT MscL, the curves are steeper, which correlates with higher cooperativity of gating, whereas the lower slope of V23T curves is ascribed to high occupancy of subconductive states at low tensions and pre-expanded closed state[3]

Summary

Introduction

Transmembrane voltage is a critical parameter for most ion channels because (i) it provides the driving force for ions and (ii) it is a powerful factor in triggering and modulating channel gating. We describe a strong modulation of the bacterial mechanosensitive channel MscL and especially its mild gain-of-function mutant (V23T)[3], which is apparently exerted through a non-specific dielectric mechanism by water present in the pore, with some contribution from the dipole moment of the protein itself. This mutation was suggested to produce excessive solvation and partial expansion of the normally vapour-locked MscL pore[4]. The data obtained in DIBs confirm that V23T MscL senses the local intramembrane electric field in the membrane core between the interfacial layers, and the voltage imposed by external electrodes is sensed not directly, but rather in combination with the potential imparted by the lipids

Methods

Results

Conclusion