Force spectroscopy on model membranes. (a) Atomic force microscopy on a localized free-standing lipid bilayer (FLB) (adapted from (36). A localized FLB is created by forming a supported lipid bilayer (SLB) on a substrate with sub-micrometer pores (top). A cantilever with a probe that specifically binds to bacteriorhodopsin on the FLB applies force, generating a force-distance curve for the membrane protein extension (bottom). (b) Optical tweezers on a spherical SLB (adapted from (42). A spherical SLB on a silica bead enables optical trapping (left). A DNA handle anchored on a polystyrene bead held by a second optical trap is linked to the membrane-binding protein (E-Syt). Force is then applied to generate the force-extension curve (right). (c) Magnetic tweezers on bicelle and liposome (adapted from (55). Transmembrane proteins (β2-AR and GlpG) are reconstituted into a bicelle or a liposome, with force applied through their termini.
