Membrane-induced step in the activation of Sendai virus fusion protein

Peptides derived from conserved heptad-repeat regions of several viruses ha ve been shown recently to inhibit virus-cell fusion. To find out their poss ible role in the fusion process, two biologically active heptad-repeat segm ents of the fusion protein (F) of Sendai virus, SV-150 (residues 150-186), and SV-473 (residues 473-495) were synthesized, fluorescently labeled and s pectroscopically characterized for their structure and organization in solu tion and within the membrane. SV-150 was found to be 50-fold less active th an SV-473 in inhibiting Sendai virus-cell fusion. Circular dichroism (CD) s pectroscopy revealed that in aqueous solution, the peptides are self-associ ated and adopt low alpha-helical structure. However, when the two peptides are mixed together, their alpha-helical content significantly increases. Fl uorescence studies, CD, and polarized attenuated total reflection infrared (ATR-FTIR) spectroscopy showed that both peptides, alone or as a complex, b ind strongly to negatively charged and zwitterionic phospholipid membranes, dissociate therein into alpha-helical monomers, but do not perturb the lip id packing of the membrane. The ability of the peptides to interact with ea ch other in solution may be correlated with antiviral activity, whereas the ir ability to interact with the membrane, together with their location near the fusion peptide and the transmembrane domain, suggests a revision to th e currently accepted model for viral-induced membrane fusion. in the revise d model, in the sequence of events associated with viral entry, the two hep tad-repeat sequences may assist in bringing the viral and cellular membrane s closer, thus facilitating membrane fusion. (C) 1999 Academic Press.