CHARACTERIZATION OF MURINE GAMMAHERPESVIRUS-68 GLYCOPROTEIN-B (GB) HOMOLOG - SIMILARITY TO EPSTEIN-BARR-VIRUS GB (GP110)

Murine gammaherpesvirus 68 (MHV-68) is a natural pathogen of murid rod ents and displays similar pathobiological characteristics to those of the human gammaherpesvirus Epstein-Barr virus (EBV). However, in contr ast to EBV, MHV-68 will replicate in epithelial cells in vitro. It has therefore been proposed that MHV-68 may be of use as a model for the study of gammaherpesviruses, EBV in particular, both in vitro and in v ivo. The EBV homolog of herpes simplex virus glycoprotein B (gB), term ed gp110, is somewhat unusual compared with those of many other herpes viruses. We therefore decided to characterize the homolog of gB encode d by MHV-68 (termed MHV gB) to observe the properties of a gammaherpes virus gB produced in epithelial cells and also to test the relatedness of MHV-68 and EBV. The MHV gB-coding sequence was determined from clo ned DNA. The predicted amino acid sequence shared closest homology wit h gammaherpesvirus gB homologs. Biochemical analysis showed that MHV g B was a glycoprotein with a molecular weight of 105,000. However, the glycans were of the N-linked, high-mannose type, indicating retention in the endoplasmic reticulum. In line with this, MHV gB was localized to the cytoplasm and nuclear margins of infected cells but was not det ected on the cell surface or in virions. Additionally, anti-MHV gB ant isera were nonneutralizing. Thus, the MHV gB was unlike many other her pesvirus gBs but was extremely similar to the EBV gB. This highlights the close relationship between MW 68 and EBV and underlines the potent ial of MHV-68 as a model for EBV in epithelial cells both in vitro and in vivo.