Thermodynamicsof interaction between a small peptide derived from glycoprotein gp36 of Feline Immunodeficiency Virus and model membrane sistems

The interactions between peptides and lipid bilayers are fundamental in a variety of key biological processes and among these the fusion process by viral proteins is one of the most important. A great number of viruses (e.g. human immunodeficiency virus) have a lipid double layer rich in glycoproteins, which through a series of fission and fusion events, allows the infection of host cell to occur1. It is known that the glycoprotein gp 36 of the feline immunodeficiency virus (FIV) has a key role in the fusion process. Particularly, it was found that a small region of 8 residues of the membrane proximal external region (MPER), rich in Trp residues, is of fundamental importance2. In this study, we performed a physicochemical characterization of the interaction process between a small peptide, named C8 derived from MPER of FIV, and some biological membrane models (liposomes). ITC measurements have shown that the interaction between C8 and liposomes depends on the lipid composition. Particularly, the peptide C8 interacts with liposomes composed of POPC, POPC/POPG and POPC/SM whereas no interaction was observed with the Chol-containing membranes. DSC studies with liposomes of DPPC, DPPC/Chol and POPC/SM indicated that the peptide interacts preferentially with zwitterionic polar headgroups affecting dramatically the thermotropic properties of the double layer. Circular dichroism studies have shown that the conformation of the peptide changes upon binding to the liposomes. Interestingly the peptide changes its structure and folds from a disordered structure (in the absence of liposomes) to a more ordered structure with a low but significantly helix-content. In conclusion this study can provide fundamental insights into the role of this short fragment in the infection process.