Mechanics of Droplet Interface Bilayer “Unzipping” Defines the Bandwidth for the Mechanotransduction Response of Reconstituted MscL

Fully fluidic three-phase droplet interface bilayers (DIBs) are convenient systems for studies of physiochemical properties of lipid-stabilized interfaces as well as for reconstitution of biological molecules involved in ion transport, sensing, and energy conversion. Recently, it was reported that the low-threshold mutant of the bacterial mechanosensitive channel MscL can be transiently activated in DIBs under harmonic mechanical stimulation. However, the experimentally determined range of oscillation frequencies generating sufficient tension for MscL gating is narrow (0.1–0.3 Hz). Here, physical parameters of the system that define tension in the interface bilayer under equilibrium and dynamic regimes and their variations during viscoelastic responses of droplets to compression and retraction, are analyzed. It is found that the rate of interfacial bilayer “unzipping” during the retraction phase limits the process of droplet area relaxation, thus preventing tensile expansion in the subsequent cycles. This article proposes temporally asymmetric stimulation protocols with variable ratio of compression to retraction phases (duty cycle), which allows the slow shape relaxation process and stimulates MscL much more efficiently. The new protocol activates a larger proportion of MscL's fully open states relative to the population of subconductive states over a wider range of frequencies.