Dramatic rigidification of a peptide-decorated lamellar phase - art. no. 041903

We have performed small-angle x-ray scattering on a lamellar (L-alpha) phas e made of a nonionic surfactant (C12E4), decane, and water, after the inser tion of a triblock peptide. The hydrophilic part of the peptide is rigid an d organized in an a helix in the presence of membranes. Surface tension mea surements and spectrofluorometry show that the peptide lies on the membrane surface. The Caille parameter eta and the smectic compressibility modulus (B) over bar decrease with peptide concentration, whereas the membrane bend ing rigidity kappa increases threefold for mole ratio of peptide to surfact ant as low as 5.2x10(-4). The published models for rigid inclusions in memb ranes cannot account for this dramatic rigidification. However, experimenta l results are well fitted by a Heuristic renormalization of the membrane th ickness.