This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.Membrane fusion is an essential process for a variety of cellular events. In particular, it is the basic mode of entry by enveloped viruses into cells. Viral fusion proteins contain segments of 10-30 residues, called fusion peptides (FP), which insert into the host cell membrane. Their insertion is followed by formation of a fusion pore and by merging of the viral membrane into the host membrane. Here we propose to investigate the effects of FP on the behavior of lipid membrane dispersions able to transform from lamellar into inverted bicontinuous cubic phase. The latter transformation actually occurs as a result of multiple, cooperative fusion events and thus represents an appropriate model of fusion pore formation (Fig. 1). Time-resolved X-ray diffraction is the method of choice for studies on the pathway and kinetics of this transition. We have collected X-ray diffraction evidence a documenting the ability of major membrane lipid classes to transform from lamellar into well-ordered bilayer cubic phases. In preliminary work, we found that FP strongly favor and accelerate cubic phase formation. These findings make it possible to focus on their structural roles in the present project. Using sets of synthetic, well defined wild-type and mutant, non-functional peptide sequences, our major goal is to characterize in a novel, quantitative way the FP effects on the membrane structure and stability. We also plan to investigate the observed lipid specificity of some FPs and to elucidate and quantify the fusion competence of the major biomembrane lipid classes.
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