Unbinding-binding transition induced by molecular snaps in model membranes

We have used a lamellar phase made of a nonionic surfactant, dodecane and w ater, as a model membrane to investigate its interactions with macromolecul ar inclusions bringing together two membranes, i.e., acting as macromolecul ar snaps. In systems devoid of inclusions, the interlamellar distance depen ds on the total volume fraction of membranes Phi. We show that, in presence of a transmembrane protein, or of several de novo designed peptides of dif ferent length and composition, the lamellar phase undergoes a binding trans ition. Under such conditions, the interlamellar distance is no longer propo rtional to Phi(-1), but rather to the surface concentration of snaps within the membrane. It also appears that, in the presence of the hydrophobic seg ment of peptide snaps, the length of the inclusions must be at least equal to the hydrophobic length of the membrane to be active. Experimental result s have been precisely fitted to a model of thermally stabilized membranes, decorated with snaps. However, in the presence of inclusions, the parameter describing the interactions between membranes, has to take into account th e length of the inclusion to preserve good predictive capabilities.