Mode of action of two inhibitory peptides from heptad repeat domains of the fusion protein of Newcastle disease virus

Abstract

Peptides derived from heptad repeat (HR) sequences of viral fusion proteins from several enveloped viruses have been shown to inhibit virus-mediated membrane fusion but the mechanism remains unknown. To further investigate this, the inhibition mechanism of two HR-derived peptides from the fusion protein of the paramyxovirus Newcastle disease virus (NDV) was investigated. Peptide N24 (residues 145–168) derived from HR1 was found to be 145-fold more inhibitory in a syncytium assay than peptide C24 (residues 474–496), derived from HR2. Both peptides failed to block lipid-mixing between R18-labeled virus and cells. None of the peptides interfered with the binding of hemagglutinin–neuraminidase (HN) protein to the target cells, as demonstrated by hemagglutining assays. When both peptides were mixed at equimolar concentrations, their inhibitory effect was abolished. In addition, both peptides induced the aggregation of negatively charged and zwitterionic phospholipid membranes. The ability of the peptides to interact with each other in solution suggests that these peptides may bind to the opposite HR region on the protein whereas their ability to interact with membranes as well as their failure to block lipid transfer suggest a second binding site. Taken together these results, suggest a mode of action for C24 and N24 in which both peptides have two different targets on the F protein: the opposite HR sequence and their corresponding domains.