Cloning and characterization of rhesus cytomegalovirus glycoprotein B

This study describes the molecular cloning and characterization of the glycoprotein B (gB) gene from rhesus cytomegalovirus (RhCMV), a virus that naturally infects rhesus macaques. The researchers isolated the gB gene from RhCMV strain 68-1, sequenced it completely, and analyzed its expression and protein properties. The RhCMV gB gene encodes a predicted protein of 854 amino acids that shares 60% identity and 75% similarity with human cytomegalovirus (HCMV) gB protein. Notably, the region implicated in viral binding, fusion, and cell-to-cell spread showed the highest conservation at 74% identity. Northern blot analysis revealed that RhCMV gB is transcribed as a late gene, differing from HCMV where gB is transcribed early but translated late. Metabolic labeling demonstrated that RhCMV gB undergoes proteolytic processing similar to HCMV gB, producing processed fragments of approximately 50 and 80 kilodaltons. The researchers also identified strong conservation of structural features including cysteine residues and N-linked glycosylation sites. Cross-reactive epitopes were detected using anti-HCMV monoclonal antibodies, indicating preserved immunogenic properties between primate CMV species.

Key findings

• RhCMV gB encodes an 854-amino acid protein that is 60% identical to HCMV gB, with 74% identity in the region responsible for virus binding and cell-to-cell spread
• RhCMV gB is transcribed as a late gene dependent on viral DNA replication, unlike HCMV gB which is transcribed as an early gene
• The protein undergoes proteolytic processing similar to HCMV, producing functional cleavage products of approximately 50 and 80 kilodaltons
• Eleven of twelve cysteine residues and fourteen of sixteen potential N-linked glycosylation sites are conserved between RhCMV and HCMV gB proteins
• Anti-HCMV gB monoclonal antibodies cross-react with RhCMV gB, indicating conservation of immunogenic epitopes in primate CMV species