Biophysical investigation of biomolecules in bio-membrane models

Many drugs are available for the treatment of systemic or superficial mycoses,but only a limited number of them are effective antifungal drugs, devoid oftoxic and undesirable side effects. Therefore there remains an urgent need fora new generation of antifungal agents.The present work concerns the synthesis, the antifungal activity and thebiophysical characterization of a set of linear and cyclic peptides (AMT1,cyclo-AMT1, AMT2, cyclo-AMT2, AMT3, cyclo-AMT3) includingaminoacids characteristic of membrane-active antimicrobial peptides (AMP).The peptides were tested against different yeast species, and displayed generalantifungal activity, with a therapeutically promising antifungal specificityagainst Cryptococcus neoformans.To shed light on the role played by the membrane cell in the antifungalactivity an extensive biophysical study was carried out using differentspectroscopic techniques. Our structural investigation provides data to excludethe ability of the peptides to penetrate the membrane of the fungal cell,highlighting their attitude to interact with the external surface of the bilayer.Taken together our data support the hypothesis that the membrane cell of thefungi may be an important platform for specific interactions of the synthesizedpeptides with more specific targets involved in the cell wall synthesis.Viral fusion glycoproteins present a membrane-proximal external region(MPER) which is usually rich in aromatic residues and presents a markedtendency to stably reside at the membrane interfaces, leading, throughunknown mechanisms, to a destabilization of the bilayer structure. This step has been proposed to be fundamental for the fusion process between targetmembrane and viral envelope. In present work, we investigate the interactionbetween an octapeptide (C8) deriving from the MPER domain of gp36 ofFeline Immunodeficiency Virus and different membrane models by combiningexperimental results obtained by Nuclear Magnetic Resonance, Electron SpinResonance, Circular Dichroism and Fluorescence Spectroscopy withMolecular Dynamics simulations. Our data indicate that C8 binds to the lipidbilayer adsorbing onto the membrane surface without deep penetration. As aconsequence of this interaction, the bilayer thickness decreases. Theassociation of the peptide with the lipid membrane is driven by hydrogenbonds as well as hydrophobic interactions that the Trp side chains form withthe lipid headgroups. Notably these interactions may be the key to interpret atmolecular level the function played by Trp residues in all the fragments ofviral envelope involved in fusion mechanism with target membrane. [edited by author]