Dramatic rigidification of a peptide-decorated lamellar phase

We have performed small-angle x-ray scattering on a lamellar (L_α) 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 α helix in the presence of membranes. Surface tension measurements and spectrofluorometry show that the peptide lies on the membrane surface. The Caillé parameter η and the smectic compressibility modulus B̅ decrease with peptide concentration, whereas the membrane bending rigidity κ increases threefold for mole ratio of peptide to surfactant as low as 5.2×10^-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.