Structure and composition of a family of human cytomegalovirus glycoprotein complexes designated gC-I (gB)

Abstract

Murine monoclonal antibodies (MAbs) were made to the 52 000 (gp52) and the 93 000 to 130 000 Mr (gp93-130) glycoproteins from a human cytomegalovirus (HCMV) glycoprotein complex designated gC-I or the gB homoglogue. MAbs recognizing either gp52 or gp93-130 could immunoprecipitate unreduced gC-I complexes from non-ionic detergent extracts of HCMV. Western blotting was performed with immunoaffinity-purified gC-I complexes which were reduced prior to analysis. MAbs made against gp52 recognized gp52 and a 158 000 Mr glycoprotein (gp 158). MAbs which recognized gp93-130 in a Western blot also reacted with gp158, which is a gC-I precursor glycoprotein. The origin of gp93-130 was demonstrated by the reactivity of our gp93-130 MAbs with a recombinant protein containing the N-terminal portion of the gB gene. These data are consistent with the hypothesis that gp52 and gp93-130 are generated from the same high Mr precursor by proteolysis. MAbs recognizing either gp52 or gp93-130 neutralized Towne strain HCMV, but MAbs recognizing gp52 required complement to neutralize whereas MAbs recognizing gp93-130 did not. It was also determined that gp93-130 and gp158 have detectable amounts of O-linked glycans but gp52 does not, showing a difference in the glycosylation of these glycoproteins. Analysis of gC-I disulphide bonds showed that two types were present, one which was very susceptible to reduction and a second which was less susceptible. These complexes could consist of very susceptible inter-complex disulphide bonds and less susceptible intra-complex disulphide bonds.