THE PRESENCE OF UDP-N-ACETYLGLUCOSAMINE - ALPHA-3-D-MANNOSIDE BETA-1,2-N-ACETYLGLUCOSAMINYLTRANSFERASE-I ACTIVITY IN SPODOPTERA-FRUGIPERDA CELLS (IPLB-SF-21AE) AND ITS ENHANCEMENT AS A RESULT OF BACULOVIRUS INFECTION

A Golgi preparation from Spodoptera frugiperda (IPLB-SF-21AE) cells wa s incubated in the presence of the mannosidase II inhibitor, swainsoni ne, with the oligosaccharide, M(alpha1,3)[[M(alpha1,3)[M(al,6)]M(alpha 1,6)]] M(beta1,4)Gn(beta1,4)Gn (M5Gn2), the preferred substrate for th e enzyme, UDP-N-acetylglucosamine:alpha-3-D-mannoside beta1,2-N-acetyl glucosaminyltransferase I (Gn-TI). This resulted in formation of the p roduct, [[M(alpha1,3)[M(alpha1,6)]M(alpha1,6)]]-M(beta1,4) Gn(beta1,4) Gn (Gn(I)M5Gn2). A significantly increased (>4-fold) rate of conversio n of M5Gn2 to Gn(I)M5Gn2 occurred with insect cell-derived Golgi prepa rations that had been infected with a recombinant baculovirus for 66 h , a time at which significant amounts of complex-type oligosaccharides were assembled on a heterologous protein, human plasminogen, expresse d in this system. Coupled with previous results (Davidson, D. J., Bret thauer, R. K., and Castellino, F. J. (1991) Biochemistry 30, 9811-9815 ) that demonstrated the occurrence of virally induced activation of a specific M6-mannosidase in IPLB-SF-21AE cells, it is clear that viral infection of lepidopteran insect cells makes available enzymes that pr ovide and utilize the substrate, M5Gn2-protein. This is a key feature in the explanation of the previous original observations made by this laboratory, that lepidopteran insect cells are capable of assembly of complex-type oligosaccharides on glycoproteins.