Dramatic rigidification of a peptide-decorated lamellar phase.

We have performed small-angle x-ray scattering on a lamellar (L(alpha)) phase made of a nonionic surfactant (C12E4), decane, and water, after the insertion of a triblock peptide. The hydrophilic part of the peptide is rigid and organized in an alpha helix in the presence of membranes. Surface tension measurements and spectrofluorometry show that the peptide lies on the membrane surface. The Caillé parameter eta and the smectic compressibility modulus (-)B decrease with peptide concentration, whereas the membrane bending rigidity kappa increases threefold for mole ratio of peptide to surfactant as low as 5.2 x 10(-4). The published models for rigid inclusions in membranes cannot account for this dramatic rigidification. However, experimental results are well fitted by a Heuristic renormalization of the membrane thickness.