HOMODIMERIC ASSOCIATION OF THE SPIKE GLYCOPROTEIN-G1 AND GLYCOPROTEIN-G2 OF UUKUNIEMI-VIRUS

We have studied the interactions of the G1 and G2 membrane glycoprotei ns of Uukuniemi virus, a bunyavirus, in virus particles and in Triton X-100-solubilized virus. The G1 glycoprotein in intact virus or in Tri ton solution could be oxidized into a covalent homodimer using Cu2+ io n as a catalyst. Immunoprecipitations of the glycoproteins from Triton -solubilized virus lysates showed that G1 and G2 do not form a stable heterodimeric or heterooligomeric complex. The oligomeric association of G1 and G2 was further analyzed using centrifugation in sucrose grad ients in the presence of Triton X-100. The results indicate that G1 ex ists as a Triton-resistant pH-insensitive homodimer. This is in contra st to the behavior of G2, which exists as a homodimer and partially as a monomer at pH 6.4 or above and is dissociated completely into a mon omer at pH 6.0 or below. The threshold for the dimer-monomer shift of G2 is between pH 6.2 and pH 6.0. Electron microscopy studies show that the surface structure of the virus particle undergoes a pH-dependent change. Studies on the kinetics of virus entry suggest that pH below 6 .2 is necessary for the penetration of Uukuniemi virus. (C) 1995 Acade mic Press, Inc.