Chimeras Reveal a Single Lipid-Interface Residue that Controls MscL Channel Kinetics as well as Mechanosensitivity

SummaryMscL, the highly conserved bacterial mechanosensitive channel of large conductance, serves as an osmotic “emergency release valve,” is among the best-studied mechanosensors, and is a paradigm of how a channel senses and responds to membrane tension. Although all homologs tested thus far encode channel activity, many show functional differences. We tested Escherichia coli and Staphylococcus aureus chimeras and found that the periplasmic region of the protein, particularly E. coli I49 and the equivalent S. aureus F47 at the periplasmic lipid-aqueous interface of the first transmembrane domain, drastically influences both the open dwell time and the threshold of channel opening. One mutant shows a severe hysteresis, confirming the importance of this residue in determining the energy barriers for channel gating. We propose that this site acts similarly to a spring for a clasp knife, adjusting the resistance for obtaining and stabilizing an open or closed channel structure.

Graphical AbstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► MscL from E. coli and S. aureus are functionally distinct mechanosensitive channels ► MscL chimeras allow correlation of structural differences with functional variance ► Residue hydropathy at one site influences gating and state stabilization of MscL ► One residue can vary MscL activity similarly to adjusting a spring of a clasp knife