Structure of the altered oligosaccharide present in glycoproteins from a clone of Chinese hamster ovary cells deficient in N-acetylglucosaminyltransferase activity.

Clone 15B cells, derived from Chinese hamster ovary cells and deficient in a specific UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminyltransferase activity, synthesize glycoproteins with altered oligosaccharide units. Glycopeptides prepared from these glycoproteins contain large quantities of a glycopeptide with the composition (Man)5(GlcNAc)2-Asn whereas parent cells have only small amounts of this glycopeptide. The structure of the glycopeptide was determined by the combination of methylation analysis, acetolysis, Smith periodate degradation, and alpha- and beta-mannosidase digestion. Its complete structure is Manalpha 1 leads to 6[Manalpha1 leads to 3]-Manalpha1 leads to 6[Manalpha 1 leads to 3]-Manbeta1 leads to 4 GlcNAcbeta1 leads to 4 GlcNAc leads to Asn-peptide. The structures of two other glycopeptides found in smaller quantities in clone 15B but not detected in the parent cells were determined and are Manalpha 1 leads to 6 [Manalpha 1 leads to 3]-Manalpha1 leads to 6Manbeta 1 leads to 4 GlcNAcbeta 1 leads to 4GlcNAc-Asn-peptide and Manalpha 1 leads to 3 Manalpha 1 leads to 6[Manalpha 1 leads to 3] Manbeta 1 leads to 4GlcNAcbeta 1 leads to 4GlcNAc-Asn-peptide. It is proposed that the (Man)5(GlcNAc)2-Asn unit is the physiologic acceptor for the particular N-acetylglucosaminyltransferase which is deficient in clone 15B cells and that this reaction is necessary for complex oligosacchari-e biosynthesis.