Robust single membrane protein tweezers

Single-molecule tweezers, such as magnetic tweezers, are powerful mechanical manipulation tools that can probe nm-scale structural changes in a single membrane protein under force. However, the weak molecular tethers used in the tweezers limit a long time, repetitive mechanical manipulation because of their force-induced bond breakage. Here, using the metal-free click chemistry of dibenzocyclooctyne (DBCO) cycloaddition and the rapid, strong binding of traptavidin to dual biotins (2xbiotin), we developed robust single-molecule tweezers that can perform thousands of force applications on a single membrane protein. By applying up to 50 pN for each cycle, which is sufficiently high for most biological processes, we were able to observe repetitive forced unfolding for a designer membrane protein up to approximately 1000 times on average. Monte Carlo simulations showed that the average error of the unfolding kinetic values rapidly decays to 1.8% at 200-time pulling, indicating that our method can quickly produce reliable statistics. The approach established here is also applicable to highly polar DNA molecules, permitting the nanomechanical manipulation of diverse biomolecular systems.