Interference with glycosylation of glycoproteins. Inhibition of formation of lipid-linked oligosaccharides in vivo

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Abstract
Influenza-virus-infected cells were labeled with radioactive sugars and extracted to give fractions containing lipid-linked oligosaccharides and glycoproteins. The oligosaccharides linked to lipid were of the high-mannose type and contained glucose. In the glycoprotein fraction, radioactivity was associated with virus proteins and occurred predominantly in the high-mannose type of glycopeptides. In the presence of the inhibitors 2-deoxy-D-glucose, 2-deoxy-2-amino-D-glucose (glucosamine), 2-deoxy-2-fluoro-D-glucose and 2-deoxy-2-fluoro-D-mannose incorporation of radiolabeled sugars into lipid- and protein-linked oligosaccharides was decreased. Kinetic analysis showed that the inhibitors affected first the assembly of lipid-linked oligosaccharides and then protein glycosylation after a lag period. During inhibition by deoxyglucose and the fluoro sugars lipid-linked oligosaccahrides were formed that contained oligosaccharides of decreased MW. No such aberrant forms were found during inhibition by glucosamine. In the case of inhibition by deoxyglucose, the aberrant oligosaccharides were not transferred to protein. Inhibition of formation of lipid-linked oligosaccharides by deoxyglucose and fluoro sugars was antagonized by mannose, in which case oligosaccharides of normal MW were formed. The inhibition by glucosamine was reversed by its removal from the medium. The reversible effects of these inhibitors exemplify their usefulness as tools in the study of glycosylation processes.