Stepwise and cooperative membrane binding and tethering of extended synaptotagmins revealed by optical tweezers

Extended synaptotagmins (E-Syts) mediate lipid exchange between endoplasmic reticulum (ER) and the plasma membrane (PM). Anchored on ER, E-Syts bind PM via a tandem array of C2 domains in a calcium-dependent manner, drawing the two membranes close to facilitate lipid exchange. How these C2 domains bind PM and regulate the ER-PM distance has not been well understood. Recently, we developed a single-molecule approach based on optical tweezers to characterizing protein-membrane interactions. Here, we applied the approach to dissect membrane binding and tethering by E-Syt1 and E-Syt2.