Approaches for the modulation of mechanosensitive MscL channel pores

Abstract

MscL was the first mechanosensitive ion channel identified in bacteria. The channel opens its large pore when the turgor pressure of the cytoplasm increases close to the lytic limit of the cellular membrane. Despite their ubiquity across organisms, their importance in biological processes, and the likelihood that they are one of the oldest mechanisms of sensory activation in cells, the exact molecular mechanism by which these channels sense changes in lateral tension is not fully understood. Modulation of the channel has been key to understanding important aspects of the structure and function of MscL, but a lack of molecular triggers of these channels hindered early developments in the field. Initial attempts to activate mechanosensitive channels and stabilize functionally relevant expanded or open states relied on mutations and associated post-translational modifications that were often cysteine reactive. These sulfhydryl reagents positioned at key residues have allowed the engineering of MscL channels for biotechnological purposes. Other studies have modulated MscL by altering membrane properties, such as lipid composition and physical properties. More recently, a variety of structurally distinct agonists have been shown bind to MscL directly, close to a transmembrane pocket that has been shown to have an important role in channel mechanical gating. These agonists have the potential to be developed further into antimicrobial therapies that target MscL, by considering the structural landscape and properties of these pockets.

The efficacy of the food-grade antimicrobial xanthorrhizol against Staphylococcus aureus is associated with McsL channel expression

“…This assumption is supported by our findings that a mutant strain of S. aureus lacking the mscL gene remained sensitive to xanthorrhizol, but at concentrations higher than those observed for the wild-type strain ( Figures 3A , 4B ). Xanthorrhizol appears to share some of its antimicrobial properties with curcumin, which also limits bacterial growth in a MscL-dependent manner and increases the activity of MscL channels, possibly due to changes in biophysical properties of the membrane, for example by its thinning, since the direct binding site for curcumin has not been identified ( Wray et al, 2021 ; Lane and Pliotas, 2023 ). Curcumin, a flavonoid polyphenol isolated from rhizome of turmeric ( Curcuma longa L.) ( Teow et al, 2016 ), which is active against both gram-negative and gram-positive bacteria, but its activity against S. aureus is less than that of xanthorrhizol ( Teow et al, 2016 ; our unpublished data).…”

Photo‐Lipids: Light‐Sensitive Nano‐Switches to Control Membrane Properties

“…The mechanosensitive channel of large conductance (MscL), which protects bacteria against strong osmotic variations, is a prototype of mechanosensitive protein channels [68] . Although it was suggested that the protein senses variations of membrane thickness, [69] the exact mechanism by which MscL is activated is not fully understood [70] . In an early study, it was found that the isomerization of di‐(5‐{[4‐(4‐butylphenyl)azo]phenoxy}pentyl)phosphate (4‐Azo‐5P), in which both acyl chains are functionalized with an azobenzene group (Figure S2C), can increase the opening probability of MscL in a reversible manner following long irradiation times (30–140 seconds) [71] .…”

“…[68] Although it was suggested that the protein senses variations of membrane thickness, [69] the exact mechanism by which MscL is activated is not fully understood. [70] In an early study, it was found that the isomerization of di-(5-{[4-(4-butylphenyl)azo]-phenoxy}pentyl)phosphate (4-Azo-5P), in which both acyl chains are functionalized with an azobenzene group (Figure S2C), can increase the opening probability of MscL in a reversible manner following long irradiation times (30-140 seconds). [71] Later on, Booth and co-workers [72] reconstituted MscL in DOPC/DOPG (1 : 1, w/v) lipid vesicles doped with up to 10 % (w : v) of 4-Azo-5P.…”