Unbinding-binding transition induced by molecular snaps in model membranes.

We have used a lamellar phase made of a nonionic surfactant, dodecane and water, as a model membrane to investigate its interactions with macromolecular inclusions bringing together two membranes, i.e., acting as macromolecular snaps. In systems devoid of inclusions, the interlamellar distance depends 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 different length and composition, the lamellar phase undergoes a binding transition. Under such conditions, the interlamellar distance is no longer proportional to Phi(-1), but rather to the surface concentration of snaps within the membrane. It also appears that, in the presence of the hydrophobic segment of peptide snaps, the length of the inclusions must be at least equal to the hydrophobic length of the membrane to be active. Experimental results 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 the length of the inclusion to preserve good predictive capabilities.