Interaction of the Third Helix of Antennapedia Homeodomain with a Deposited Phospholipid Bilayer: A Neutron Reflectivity Structural Study

Abstract

Neutron reflectivity has been used to study the structure of deposited phospholipid bilayers in the gel phase and the modifications induced by the presence of a 16 amino acid peptide, the third helix of the Antennapedia homeodomain, p-Antp43-58. The phospholipids were dipalmitoyl phosphatidylcholine (DPPC) and mixtures of DPPC with 10% mol/mol of the negatively charged dipalmitoyl phosphatidylserine (DPPS). They were deposited on silicon single crystals by using the Langmuir−Schaeffer technique. By pushing the resolution of neutron reflectivity measurements, the bilayer structure was determined at 1 A precision. The thickness of the thin water layer between the substrate and the phospholipids was found to be 5 ± 1 A, that of the headgroups 9 ± 1 A and that of the chains 36 ± 1 A. The deposited bilayer had the same roughness, 5 ± 1 A, as the substrate itself. After peptide insertion, the thickness and roughness of DPPC bilayers did not change while the peptide appeared uniformly distributed in the interfac...