Pocket delipidation induced by membrane tension or modification leads to a structurally analogous mechanosensitive channel state

Bolin Wang,Benjamin J Lane,Charalampos Kapsalis,James R Ault,Frank Sobott,Hassane El Mkami,Antonio N Calabrese,Antreas C Kalli,Christos Pliotas

doi:10.1016/j.str.2021.12.004

Abstract

SummaryThe mechanosensitive ion channel of large conductance MscL gates in response to membrane tension changes. Lipid removal from transmembrane pockets leads to a concerted structural and functional MscL response, but it remains unknown whether there is a correlation between the tension-mediated state and the state derived by pocket delipidation in the absence of tension. Here, we combined pulsed electron paramagnetic resonance spectroscopy and hydrogen-deuterium exchange mass spectrometry, coupled with molecular dynamics simulations under membrane tension, to investigate the structural changes associated with the distinctively derived states. Whether it is tension- or modification-mediated pocket delipidation, we find that MscL samples a similar expanded subconducting state. This is the final step of the delipidation pathway, but only an intermediate stop on the tension-mediated path, with additional tension triggering further channel opening. Our findings hint at synergistic modes of regulation by lipid molecules in membrane tension-activated mechanosensitive channels.

Highlights

The mechanical response of MscL suggested that pocket-targeting lipids could act as negative allosteric modulators for MS channels and that tension could be mimicked by molecules or gain-of-function mutations targeting the pocket region, which could disrupt the lipid pathway between the bulk membrane and the pockets to gate the channel (Anishkin et al, 2005; Iscla et al, 2015; Kapsalis et al, 2019; Pliotas and Naismith, 2016)
Monitoring channel gating by pocket delipidation with Hydrogen-deuterium exchange mass spectrometry (HDX-MS) The substitution of a tryptophan at position L89 in Mycobacterium tuberculosis MscL (TbMscL) has been shown to restrict lipid access to channel pockets and destabilize the closed state, leading to an expanded MscL state (Kapsalis et al, 2019)
To explore the structural transitions occurring between the two states, we used HDX-MS to measure relative differences in deuterium uptake between the wild-type (WT) and L89W channel proteins

Summary

Introduction

Specific lipid binding events and changes in transbilayer pressure can modulate the structure of membrane proteins and regulate their function (Brohawn, 2015; Cox et al, 2015; Kapsalis et al, 2019; Laganowsky et al, 2014; Malcolm et al, 2015; Naismith and Booth, 2012; Patrick et al, 2018; Pliotas et al, 2015; Pliotas and Naismith, 2016; Ridone et al, 2018; Teng et al, 2015). The mechanical response of MscL suggested that pocket-targeting lipids could act as negative allosteric modulators for MS channels and that tension could be mimicked by molecules or gain-of-function mutations (or modifications) targeting the pocket region, which could disrupt the lipid pathway between the bulk membrane and the pockets to gate the channel (Anishkin et al, 2005; Iscla et al, 2015; Kapsalis et al, 2019; Pliotas and Naismith, 2016) The function of both MscL and MscS can Structure 30, 1–15, April 7, 2022 a 2021 The Authors.

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Conclusion