Glycobiotechnology of the Insect Cell-Baculovirus Expression System

The insect cell-baculovirus expression system technology (BEST) has a prominent role in producing recombinant proteins to be used as research and diagnostic reagents and vaccines. The glycosylation profile of proteins produced by the BEST is composed predominantly of terminal mannose glycans, and, in Trichoplusia ni cell lines, core alpha 3 fucosylation, a profile different to that in mammals. Insects contain all the enzymatic activities needed for complex N- and Oglycosylation and sialylation, although few reports of complex glycosylation and sialylation by the BEST exist. The insect cell line and culture conditions determine the glycosylation profile of proteins produced by the BEST. The promoter used, dissolved oxygen tension, presence of sugar precursors, bovine serum or hemolymph, temperature, and the time of harvest all influence glycosylation, although more research is needed. The lack of activity of glycosylation enzymes possibly results from the transcription regulation and stress imposed by baculovirus infection. To solve this limitation, the glycosylation pathway of insect cells has been engineered to produce complex sialylated glycans and to eliminate alpha 3 fucosylation, either by generating transgenic cell lines or by using baculovirus vectors. These strategies have been successful. Complex glycosylation, sialylation, and inhibition of alpha 3 fucosylation have been achieved, although the majority of glycans still have terminal mannose residues. The implication of insect glycosylation in the proteins produced by the BEST is discussed.