Structure of the high mannose oligosaccharides of a human IgM myeloma protein. II. The minor oligosaccharides of high mannose glycopeptide.

The high mannose glycopeptide I from IgM (Patient Wa) contains, in addition to the two major oligosaccharides described earlier (Chapman, A., and Kornfeld, R. (1979) J. Biol Chem. 254, 816-823), four minor oligosaccharides. After release from glycopeptide I by endo-beta-N-acetylglucosaminidase Cu and reduction with NaBH4, all four oligosaccharides have been shown to have the basic structure: (see article of journal). Oligosaccharide IA-1 (Man9GlcitolNAc) has additional alpha1,2-linked mannose residues attached to positions a and b, and the sequence Man alpha1,2 yields to Man alpha1,2 yields to attached at position c. Oligosaccharide IA-2 (Man8GlcitolNAc) has additional alpha1,2-linked mannose residues attached to positions a, b, and c. Oligosaccharide IA-3 (Man7GlcitolNAc) has additional alpha1,2-linked mannose residues at positions b and c. In contrast, oligosaccharide IA-4 has a single N-acetyglucosamine residue beta1,2-linked to the mannose at position c. Oligosaccharides IA-1, -2 and -3 are thought to represent "processing" intermediates that are precursors of the major Man6 and Man5 oligosaccharides of glycopeptide I. IA-4 may arise from the Man5 oligosaccharide by the action of UDP-GlcNAc:glycoprotein N-acetylglucosaminyl-transferase, which catalyzes the first reaction leading to complex oligosaccharide synthesis.