Differential effects of lipids and lyso-lipids on the mechanosensitivity of the mechanosensitive channels MscL and MscS

Abstract

Mechanosensitive (MS) channels of small (MscS) and large (MscL) conductance are the major players in the protection of bacterial cells against hypoosmotic shock. Although a great deal is known about structure and function of these channels, much less is known about how membrane lipids may influence their mechanosensitivity and function. In this study, we use liposome coreconstitution to examine the effects of different types of lipids on MscS and MscL mechanosensitivity simultaneously using the patch-clamp technique and confocal microscopy. Fluorescence lifetime imaging (FLIM)-FRET microscopy demonstrated that coreconstitution of MscS and MscL led to clustering of these channels causing a significant increase in the MscS activation threshold. Furthermore, the MscL/MscS threshold ratio dramatically decreased in thinner compared with thicker bilayers and upon addition of cholesterol, known to affect the bilayer thickness, stiffness and pressure profile. In contrast, application of micromolar concentrations of lysophosphatidylcholine (LPC) led to an increase of the MscL/MscS threshold ratio. These data suggest that differences in hydrophobic mismatch and bilayer stiffness, change in transbilayer pressure profile, and close proximity of MscL and MscS affect the structural dynamics of both channels to a different extent. Our findings may have far-reaching implications for other types of ion channels and membrane proteins that, like MscL and MscS, may coexist in multiple molecular complexes and, consequently, have their activation characteristics significantly affected by changes in the lipid environment and their proximity to each other.Escherichia coli | giant spheroplasts | liposomes | amphipaths | pressure clamp

Mechanosensitivity is mediated directly by the lipid membrane in TRAAK and TREK1 K + channels

“…Symmetric activation in cells (where channels are uniformly oriented) is consistent with the idea that lateral membrane tension controls channel gating (41). Persistence of mechanosensitive gating in reconstituted proteoliposomes, where only lipid and (12,14,42). These values come from measurements of channel activation in pressurized membrane patches in which membrane curvature was measured, allowing the determination of tension using Laplace's law.…”

Feeling the hidden mechanical forces in lipid bilayer is an original sense

“…16 and 17 and citations therein). Briefly, the key observation is that purified MscL or MscS can be reconstituted into artificial bilayers and retain their mechanosensitivity, excluding the need of cytoskeleton, external tether, or accessory channel subunits as force transmitters (18,19). Because bilayers of phospholipids of different head groups (20) or fatty-acid lengths (21) support the mechanosensitivity of MscL, a lock-and-key ligand-gated mechanism need not apply.…”

The effect of local bending on gating of MscL using a representative volume element and finite element simulation

“…1 Many of the membrane proteins such as mechanosensitive (MS) ion channels are coupled to the lipid bilayer due to hydrophobic forces. [2][3][4][5][6][7] Thus, any mechanical stimuli on the lipid bilayer are expected to cause a force induced conformational change in the embedded protein as well. However, the physical basis of force transduction in mechanosensitive ion channels has not been quantitatively elucidated.…”