CHARACTERIZATION OF THE PUTATIVE FUSOGENIC DOMAIN IN VESICULAR STOMATITIS-VIRUS GLYCOPROTEIN-G

The envelope glycoprotein G of vesicular stomatitis virus induces memb rane fusion at low pH, Site-directed mutagenesis of specific amino aci ds within a segment spanning amino acids 123 to 137 of G protein, whic h is highly conserved in vesiculoviruses and was previously shown by u s to be involved in fusogenic activity (Y. Li, C. Drone, E. Sat, and a . P. Ghosh, J. Virol. 67:4070-3077, 1993), was used to determine the r ole of this region in low-ps-induced membrane fusion. The mutant glyco proteins expressed in COS cells were assayed for acid-pH-induced cell- cell fusion. Substitution of the variant Pro-123 with Leu had no effec t on the fusogenic activity, while substitution of conserved Phe-125 a nd Asp-137 with Tyr and Asn, respectively, shifted the pH optimum of m embrane fusion to a more acidic pH value and decreased the fusion effi ciency. The deletion of amino acid residues 124 to 127, 131 to 137, or 124 to 137 produced mutants defective in transport. Mutation of the c onserved residues Gly-124 and Pro-127 to Ala and to Gly or Leu, respec tively, inhibited cell-cell fusion activity by about 90% without affec ting transport of the mutant proteins to the cell surface, suggesting that these two residues may be present within the fusion peptide and t hus may be directly involved in fusion. This highly conserved domain c ontaining neutral amino acids of G protein may therefore represent the putative fusion domain of vesicular stomatitis virus G protein.