Synthesis and processing of herpes simplex virus type 1 glycoproteins gB and gC

The glycoproteins of herpes simplex virus type 1 (HSV-1) range in molecular weight from 44,000 to 130,000. The objective of this research was to define the sequence of events involved in the synthesis of the high molecular HSV-1 glycoproteins gB (120,000 MW) and gC (130,000 MW). The studies focused on: (a) the identification and characterization of the partially-glycosylated precursors to gB and gC; (b) the manner in which the precursors were processed to the mature glycoproteins; and (c) the identification of the nonglycosylated forms of gB and gC.

The enzyme endo-β-N-acetylglucosaminidase H was used to identify the presence of mannose-rich oligosaccharides on the mature glycoproteins and their precursors. The gB glycoprotein contained both mannose-rich and complex-type oligosaccharides, whereas its proposed precursor, gA, contained only mannose-rich N-glycosidically linked oligosaccharides. The gB glycoprotein synthesized in tunicamycin- or deoxyglucose-treated cells had an approximate molecular weight of 92,000 and represented the nonglycosylated form of gB.

Only N-linked oligosaccharides of the complex-type were detected on the gC glycoprotein. In addition, the presence of O-linked oligosaccharides was indicated by the incorporation of isotopically-labeled glucosamine and galactose into a gC-related glycoprotein synthesized in the presence of tunicamycin and the susceptibility of gC associated oligosaccharides to alkaline hydrolysis. Only mannose-rich N-glycosidically linked oligosaccharides were associated with the precursor of gC, designated pgC₍₁₀₅₎ (105,000 MW). Endo H digestion of pgC₍₁₀₅₎ demonstrated that the nonglycosylated form of gC had a molecular weight of 75,000. In addition, a 75,000 and a 92,000 molecular weight protein were synthesized in the presence of tunicamycin which suggests the posttranslational addition of O-linked oligosaccharides to the 75,000 MW protein. In the absence of tunicamycin, it is proposed that the O-linked oligosaccharides are added during the processing of pgC₍₁₀₅₎ to gC.

The incorporation of [³H]mannose into gB and gC glycoproteins synthesized in the presence of deoxyglucose was also examined. Glycoproteins synthesized in the presence of deoxyglucose contained both endo H sensitive and resistant oligosaccharides.

Based on this research a biosynthetic pathway for glycoproteins gB and gC is proposed.