title: Maturation of the hemagglutinin-neuraminidase and fusion glycoproteins of two biologically distinct strains of Newcastle disease virus.
abstract: We have compared the glycoproteins of two biologically distinct virulent strains of Newcastle disease virus. Cells infected by either strain AV or HP produce infections virions and the cellular surfaces have hemadsorbing activity; however, only cells infected by strain AV undergo fusion from within. We fractionated chicken embryo cells and monitored the incorporation of radioactive proteins into virions to study the sites of synthesis, cellular locations, and kinetics of virion assembly for the hemagglutinin-neuraminidase (HN) and the fusion glycoproteins of each strain. We found that the HN glycoprotein of both strains was synthesized on rough endoplasmic reticulum (ER), accumulated in low-density membranes derived from smooth ER and the plasma membrane, and appeared in virions after a 30-min delay. The fusion glycoprotein of both strains was synthesized as a precursor in rough ER and subsequently processed to the active form. However, the sites of accumulation of the fusion glycoproteins were strain-dependent. The larger subunit F1 of the fusion glycoprotein of strain AV was detected in subcellular fractions enriched for plasma membranes, while that of strain HP accumulated in denser fractions which contained internal membranes. This result suggests that differential compartmentation of viral glycoproteins may influence the expression of biologic activities such as fusion on cellular surfaces. Despite their different sites of accumulation, the F1 glycoproteins or F-related polypeptides of similar size were assembled into virions of both strains. The kinetics of incorporation of this protein into virions appear to be too rapid for migration through internal membrane systems. Furthermore, tunicamycin did not block the incorporation of F-related polypeptides into virions. A hypothesis is presented to explain the unusual behavior of the F-related proteins.
mesh_terms: D000818:Animals; D002459:Cell Fusion; D002478:Cells, Cultured; D002642:Chick Embryo; D006023:Glycoproteins / Q000378:metabolism*; D006389:Hemagglutinins, Viral; D008565:Membrane Proteins / Q000378:metabolism*; D009439:Neuraminidase / Q000378:metabolism; D009522:Newcastle disease virus / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology; D014764:Viral Proteins / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D006023:Glycoproteins; D006389:Hemagglutinins, Viral; D008565:Membrane Proteins; D011498:Protein Precursors; D014764:Viral Proteins; D014415:Tunicamycin; D009439:Neuraminidase