Individual roles of N-linked oligosaccharide chains in intracellular transport of the paramyxovirus SV5 fusion protein.

The role of N-linked glycosylation in the assembly, intracellular transport, and fusion activity of the paramyxovirus SV5 fusion (F) protein was examined. Each of the six potential glycosylation sites in the F protein was individually removed by oligonucleotide-directed mutagenesis on a cDNA clone encoding the SV5 F protein. When the mutant F proteins were expressed in eukaryotic cells using the vaccinia virus-T7 transient expression system they all had a significant change in gel mobility, indicating that all six sites in the F protein are used for the addition of N-linked oligosaccharides. All of the mutant F proteins could form a homooligomer. Removal of individual carbohydrate chains from the F2 subunit had little effect on the surface expression of the F protein. However, removal of individual carbohydrate chains from the F1 subunit had deleterious effects, which ranged from a partial delay in intracellular transport and decreased stability of the protein to severe transport delays and acute instability of the F protein.