To determine the functions of N-carbohydrate chains in human parainfluenza virus type 3 hemagglutinin-neuraminidase(HN)protein,a PCR-based site-directed mutagenesis method was used to obtain Nglycan mutants.Protein electrophoresis rate,cell surface expression,receptor binding activity,neuraminidase activity and cell fusion promotion activity were determined.The HN proteins of single mutants(G1,G2, and G4) and multiple mutants(G12,G14,G24 and G124)migrated faster than the wild-type(wt) HN protein on polyacry...