BIOCHEMICAL-ANALYSIS OF THE N-GLYCOSYLATION PATHWAY IN BACULOVIRUS-INFECTED LEPIDOPTERAN INSECT CELLS

The baculovirus-insect cell system is used routinely for foreign glyco protein production, but the precise nature of the N-glycosylation path way in this system remains unclear. Some studies indicate that these c ells cannot process N-linked oligosaccharides to complex forms contain ing outer-chain galactose and sialic acid, while others indicate that they can, In this study, we used the major virion envelope glycoprotei n of the baculovirus Autographa californica multicapsid nuclear polyhe drosis virus (AcMNPV) to probe the N-glycosylation pathway in baculovi rus-infected lepidopteran insect cells. The results showed that gp64 c ontained mannose, fucose, and probably N-acetylglucosamine, but no det ectable galactose or sialic acid, These same results were observed wit h gp64 produced in any one of three different lepidopteran insect cell lines derived from Spodoptera frugiperda, Trichoplusia ni, or Estigme ne acres, whether it was produced at relatively earlier or later times after infection. These results indicated that the gp64 produced in Ac MNPV-infected lepidopteran insect cells lacks complex N-linked oligosa ccharides containing outer-chain galactose and sialic acid. By contras t, gp64 produced in mammalian cells contained both galactose and siali c acid, and endoglycosidase digestions revealed that these sugars were constituents of N-linked, not O-linked, oligosaccharides. This showed that al least one N-linked side chain on gp64 has the potential to be processed to a complex form. Together, these results suggest either t hat AcMNPV-infected lepidopteran insect cells are unable to convert an y of the N-linked side chains on gp64 to complex structures or that ou ter-chain galactose and sialic acid residues are added to gp64 and the n removed by cellular or viral exoglycosidases. (C) 1995 Academic Pres s, Inc.