Functional analysis of the individual oligosaccharide chains of sendai virus fusion protein

The roles of N-linked glycosylation in the intracellular transport and fusion activity of the Sendai virus fusion (F) protein were studied. Each of three potential glycosylation motifs (designated g1, g2, and g3) in the F protein was mutated separately or in combination with the other sites. When the mutant F proteins were transiently expressed in COS cells, they showed significant changes in electrophoretic mobility, indicating that all three motifs in the F protein are glycosylated. Glycosylation-defective mutants which lacked the g2-oligosaccharide chain showed decreased immunoreactivity with a monoclonal antibody specific for the native conformation and were inefficiently transported to the cell surface. Such mutants, with the exception of a double mutant lacking g1 and g2-oligosaccharide chains, were also not able to induce syncytia formation when cells expressing them plus the hemagglutinin-neuraminidase protein were treated with trypsin. Mutations at the other glycosylation sites did not significantly affect the immunoreactivity with the monoclonal antibody or the efficiency of intracellular transport of the F protein. These results indicate that the N-linked oligosaccharide chain attached at g2 is important for efficient intracellular transport and for the fusion activity of the F protein.