Cyclodextrins increase membrane tension and are universal activators of mechanosensitive channels

Abstract

Significance Mechanosensitive (MS) channels play a key role in the physiology of organisms from bacteria to man. Many prokaryotic and eukaryotic MS channels respond to membrane tension. Here, we show that cyclodextrin (CD)–mediated lipid removal induces membrane tension that activates not only the mechanosensitive channel of small conductance but the structurally unrelated mechanosensitive channel of large conductance, which gates at almost lytic membrane tensions. This finding suggests that for both functional and structural studies, provided that sufficient CD is added and enough lipids are removed, any tension-sensitive ion channel can be activated. Moreover, CDs may also prove useful for the in vitro study of other membrane proteins that are sensitive to mechanical forces. The bacterial mechanosensitive channel of small conductance (MscS) has been extensively studied to understand how mechanical forces are converted into the conformational changes that underlie mechanosensitive (MS) channel gating. We showed that lipid removal by β-cyclodextrin can mimic membrane tension. Here, we show that all cyclodextrins (CDs) can activate reconstituted Escherichia coli MscS, that MscS activation by CDs depends on CD-mediated lipid removal, and that the CD amount required to gate MscS scales with the channel’s sensitivity to membrane tension. Importantly, cholesterol-loaded CDs do not activate MscS. CD-mediated lipid removal ultimately causes MscS desensitization, which we show is affected by the lipid environment. While many MS channels respond to membrane forces, generalized by the “force-from-lipids” principle, their different molecular architectures suggest that they use unique ways to convert mechanical forces into conformational changes. To test whether CDs can also be used to activate other MS channels, we chose to investigate the mechanosensitive channel of large conductance (MscL) and demonstrate that CDs can also activate this structurally unrelated channel. Since CDs can open the least tension-sensitive MS channel, MscL, they should be able to open any MS channel that responds to membrane tension. Thus, CDs emerge as a universal tool for the structural and functional characterization of unrelated MS channels.