For enveloped viruses, fusion of the viral envelope with a cellular membrane is critical for a productive
infection to occur. This fusion process is mediated by at least three classes of fusion
proteins (Class I, II, and III) based on the
protein sequence and structure. For Rift Valley fever virus (RVFV), the
glycoprotein Gc (Class II fusion
protein) mediates this fusion event following entry into the endocytic pathway, allowing the viral genome access to the cell cytoplasm. Here, we show that
peptides analogous to the RVFV Gc stem region inhibited RVFV infectivity in cell culture by inhibiting the fusion process. Further, we show that infectivity can be inhibited for diverse, unrelated RNA viruses that have Class I (Ebola virus), Class II (Andes virus), or Class III (
vesicular stomatitis virus) fusion proteins using this single
peptide. Our findings are consistent with an inhibition mechanism similar to that proposed for stem
peptide fusion inhibitors of dengue virus in which the RVFV inhibitory
peptide first binds to both the virion and cell membranes, allowing it to traffic with the virus into the endocytic pathway. Upon acidification and rearrangement of Gc, the
peptide is then able to specifically bind to Gc and prevent fusion of the viral and endocytic membranes, thus inhibiting
viral infection. These results could provide novel insights into conserved features among the three classes of
viral fusion proteins and offer direction for the future development of broadly active fusion inhibitors.