Calnexin associates with the precursors of glycoproteins B, C, and D of herpes simplex virus type 1.

By a pulse-chase approach combined with immunoprecipitation, we showed that the newly synthesized precursors of glycoprotein B (gB), glycoprotein C (gC), and glycoprotein D (gD) of herpes simplex virus type 1 (HSV-1) were associated with calnexin, a membrane-bound chaperone in the endoplasmic reticulum. Kinetics of association and dissociation was quite different among the precursors. For the precursors of gC and gD of HSV-1, the maximal association was observed immediately after the synthesis and they dissociated rapidly with half-times of 25 min for gC and 30 min for gD, respectively. In contrast, the precursor of gB showed prolonged association with calnexin. Their maximum association was observed 30 min after the synthesis, and thereafter, they dissociated slowly with a half-time of 70 min. The results suggest that, while glycoproteins that have a rapid processing rate, such as gC and gD of HSV-1, rapidly associate with calnexin and their association is quite short, those that take much time to be processed to a mature form, such as gB of HSV-1, have prolonged association kinetics with calnexin. Complete inhibition of the binding of these glycoprotein precursors to calnexin by tunicamycin or castanospermine indicates the importance of partially trimmed N-linked oligosaccharides for their association.