Topological and operational delineation of antigenic sites on the HN glycoprotein of Newcastle disease virus and their structural requirements.

Monoclonal antibodies to the hemagglutinin-neuraminidase glycoprotein of Newcastle disease virus have identified four antigenic sites on the glycoprotein, which are topologically and operationally discriminated from one another. To define the metabolisms and cellular compartments required for formation of the individual antigenic sites, a panel of monoclonal antibodies were examined for their reactivity with the nascent and variously processed forms of the antigen molecules in combination with the use of inhibitors of glycosylation (tunicamycin and N-methyl-1-deoxynojirimycin) and glycoprotein transport (carbonyl cyanide m-chlorophenylhydrazone and monensin). Reactivity was also examined with the antigen molecules deglycosylated by endoglycosidase F and with the antigen molecules reduced by 2-mercaptoethanol. The results taken together suggest that posttranslational organization of the glycoprotein is important for all four of the antigenic sites. At the same time, there appeared to be marked site-specific requirements with respect to glycosylation and disulfide bond formation. However, all of these metabolic requirements were found to be provided within the rough endoplasmic reticulum, and no further processing of the antigen molecules appeared to be necessary for the formation of any of the antigenic sites.