G. Fragneto et al., Interaction of the third helix of Antennapedia homeodomain with a deposited phospholipid bilayer: A neutron reflectivity structural study, LANGMUIR, 16(10), 2000, pp. 4581-4588
Neutron reflectivity has been used to study the structure of deposited phos
pholipid bilayers in the gel phase and the modifications induced by the pre
sence of a 16 amino acid peptide, the third helix of the Antennapedia homeo
domain,p-Antp(43-58). The phospholipids were dipalmitoyl phosphatidylcholin
e (DPPC) and mixtures of DPPC with 10% mol/mol of the negatively charged di
palmitoyl phosphatidylserine (DPPS). They were deposited on silicon single
crystals by using the Langmuir-Schaeffer technique. By pushing the resoluti
on of neutron reflectivity measurements, the bilayer structure was determin
ed at 1 Angstrom precision. The thickness of the thin water layer between t
he substrate and the phospholipids was found to be 5 +/- 1 Angstrom, that o
f the headgroups 9 +/- 1 Angstrom and that of the chains 36 +/- 1 Angstrom.
The deposited bilayer had the same roughness, 5 +/- 1 Angstrom, as the sub
strate itself. After peptide insertion, the thickness and roughness of DPPC
bilayers did not change while the peptide appeared uniformly distributed i
n the interfacial region. In the presence of 10% DPPS the peptide was mainl
y detected in the headgroup regions and its insertion induced an increase o
f the bilayer roughness up to 12 +/- 1 Angstrom. No affinity between the pe
ptide and the lipid hydrocarbon region was detected. Neutron reflectivity w
as shown once more to be a valuable technique for structural determination
and with good potential for studies of relevance in biology.