Conformationally sensitive antigenic determinants on the HN glycoprotein of Newcastle disease virus form with...

The mature Newcastle disease virus (NDV) hemagglutinin-neuraminidase (HN) protein is a type 2, oligomeric glycoprotein which has seven antigenic sites, sites 1, 2, 3, 4, 23, 12, and 14 (lorio et al., 1989, Virus Res. 13, 245). The folding of the HN protein was explored by characterizing the formation of representative epitopes specific for each of the six of antigenic sites in infected cells. None of these epitopes was present on the nascent, 5-min pulse-labeled HN protein, while all epitopes appeared after a 1- to 2-hr chase. All epitopes formed in the presence of monensin or during a chase at 15 degrees, suggesting that all these determinants appear while the molecule is in the rough endoplasmic reticulum. However, none of the epitopes appeared during chases in the presence of carbonyl cyanide m-chlorophenylhydrazone, suggesting that the formation of all determinants requires ATP. The kinetics of formation of each of the determinants was quantitated in both NDV-infected Cos cells and chick embryo cells. In both cell types, antigenic determinants formed with different kinetics. The epitope specific for site 4 appeared first, followed by the simultaneous appearance of epitopes in sites 1 and 3. The epitope in site 2 appeared next and that in site 23 last. The kinetics of appearance of the epitope in site 14 relative to those in other sites varied with cell type. In chick cells, this epitope appeared with the site 2 epitope, while in Cos cells this epitope appeared with or just after sites 1 and 3 epitopes. Nonradioactive chases at 15 degrees slowed the formation of the antigenic determinants. The disulfide-linked dimer form of the HN protein appeared concomitant with epitopes in sites 1 and 3.