Expression of the Sendai Virus Fusion Protein in Insect Cells and Characterization of its Post-translational Modifications

The fusion (F) protein of Sendai virus was expressed with a baculovirus system in insect cells. The F protein is synthesized in its uncleaved form F0, which appears in SDS-containing gels as two bands with M r values of 66K and 64K. Digestion of the F protein with endoglycosidase H revealed that the 66K species contains high mannose-type carbohydrates, whereas partially processed oligosaccharides are attached to the 64K species. Pulse-chase experiments showed that the F protein is initially synthesized as its 66K form. After 1 h of chase this precursor glycoprotein is partially converted to the 64K species and exposed at the cell surface. Other modifications of the F protein in insect cells are the formation of intramolecular disulphide linkages and oligomerization. However, processing and plasma membrane transport of the F protein in insect cells are incomplete and retarded compared to the F protein synthesized in Sendai virus-infected mammalian cells.