ASSESSMENT OF ANTIGENICITY AND GENETIC-VARIATION OF GLYCOPROTEIN-B OFMURINE CYTOMEGALOVIRUS

An analysis of linear antibody-binding sites of the glycoprotein B (gB ) molecule of murine cytomegalovirus (MCMV) and of genetic variation w ithin these regions was performed. To achieve this, a series of overla pping fragments spanning the entire coding sequence of the gB gene of the K181 strain of MCMV was expressed in E. coli as fusion proteins wi th glutathione S-transferase (GST) using the pGEX expression system. F our antibody-binding regions were mapped to locations spanning amino a cid residues 17-79 (BS), 155-278 (BE2), 809-926 (SS) and 347-508 (BE a nd EE), based on reactivity in Western blot analysis of GST-gB fusion proteins with murine polyclonal antiserum raised against MCMV. Only th e antibody-binding region BE2 (155-278) elicited an antiserum that exh ibited complement-dependent neutralizing activity, and immunization of mice with the fusion protein BE2 led to moderate but significant redu ctions in the level of MCMV replication in the spleen. Polyclonal anti sera raised against the GST-gB fusion proteins detected purified virio n proteins of 105 kDa (anti-BS and anti-BE2) and 52 kDa (anti-SS), and are therefore likely to recognize the N-terminal and C-terminal porti ons of the gB molecule, respectively. The antibody-binding region with in amino acid residues 17-79 was found to be MCMV strain-specific, whe reas antibody-binding regions within residues 155-278 and 809-926 were found to be conserved among MCMV field isolates. Comparative sequence analysis of the corresponding regions of MCMV gB revealed a level and extent of sequence heterogeneity consistent with these findings.