Dramatic rigidification of a peptide-decorated lamellar phase

Area of Science:

• Materials Science
• Biophysics
• Physical Chemistry

Background:

• Lamellar (Lα) phases formed by nonionic surfactants, alkanes, and water are model systems for cell membranes.
• Understanding how peptides interact with and modify membrane properties is crucial for biological and materials applications.
• Triblock peptides with rigid hydrophilic domains can potentially alter membrane structure and mechanics.

Purpose of the Study:

• To investigate the effect of a specific triblock peptide on the structural and mechanical properties of a nonionic surfactant lamellar phase.
• To determine the peptide's location within the membrane system.
• To elucidate the mechanism behind peptide-induced changes in membrane rigidity.

Main Methods:

• Small-angle X-ray scattering (SAXS) to probe lamellar phase structure.
• Surface tension measurements to assess interfacial properties.
• Spectrofluorometry to determine peptide localization.
• Analysis of Caillé parameter (η) and smectic compressibility modulus (B) from SAXS data.
• Determination of membrane bending rigidity (κ).

Main Results:

• The triblock peptide localizes to the membrane surface, with its hydrophilic part forming an alpha helix.
• Increasing peptide concentration leads to a decrease in the Caillé parameter (η) and smectic compressibility modulus (B).
• A threefold increase in membrane bending rigidity (κ) was observed at a peptide-to-surfactant mole ratio as low as 5.2 x 10⁻⁴.
• Existing models for rigid inclusions could not explain the observed rigidification.

Conclusions:

• The studied triblock peptide significantly rigidifies surfactant membranes.
• The experimental results are well described by a heuristic renormalization of membrane thickness, suggesting a novel mechanism for peptide-induced membrane stiffening.
• This finding has implications for designing peptide-based materials and understanding peptide-membrane interactions in biological systems.