IDENTIFICATION OF 2 AMINO-ACIDS IN THE HEMAGGLUTININ GLYCOPROTEIN OF MEASLES-VIRUS (MV) THAT GOVERN HEMADSORPTION, HELA-CELL FUSION, AND CD46 DOWN-REGULATION - PHENOTYPIC MARKERS THAT DIFFERENTIATE VACCINE ANDWILD-TYPE MV STRAINS

We have used site-directed mutagenesis of the hemagglutinin (H) glycop rotein of measles virus (MV) to investigate the molecular basis for th e phenotypic differences observed between MV vaccine strains and recen tly isolated wild-type MV strains. The former downregulate CD46, the p utative cellular receptor of MV, are positive for hemadsorption, and a re fusogenic in HeLa cells, whereas the latter are negative for these phenotypic markers. CD46 downregulation in particular, could have prof ound consequences for the immunopathology of MV infection, as this mol ecule protects the cell from complement lysis. Mutagenesis of two amin o acids, valine and tyrosine at positions 451 and 481, respectively, i n the H protein from the vaccine-like Halle MV strain to their counter parts, glutamate and asparagine, in the H protein from the wild-type M a93F MV strain (creating the V451E/Y481N double mutation) abrogated CD 46 downregulation, HeLa cell fusion, and hemadsorption, The converse d ouble mutagenesis of the Ma93F H protein (E451V/N481Y) transferred the CD16-downregulating, fusogenic, and hemadsorption functions to this p rotein, The data provide the first mapping study of the functional dom ains of MV H. The consequences of these results for AIV vaccine design and the role of CD46 in MV infection are discussed.