Structural Analysis of Glycopeptides and Glycoproteins Containing N-Glycosyl Linkages

Structural Analysis of Glycopeptides and Glycoproteins Containing N-Glycosyl Linkages 

These observations have several implications for studies of glycoproteins (i) the resonances of anomeric carbon atoms that are involved in N-glycosylic linkages will be rather difficult to identify, because of their proximity to nonanomeric-carbon resonances and (ii) due to the proximity of the chemical shifts of C-l and C-5 (they are only 0.6 p.p.m. apart for / -d-G1cNAc — Asn), it may be difficult, but not impossible, to ascertain whether N-glycosylic linkages exist in the glycoprotein (see later). 

Anomeric Chemical-shift Data67 for High-Mannose Oligopeptides Derived 

This pattern of chemical-shift nonequivalence is also manifested by the nonanomeric carbon atoms. 

A distinct feature that may not be readily noticeable is that the chemical shift of the C-l atom of an a-D-mannosyl residue is highly dependent on its residue linkage to another a-D-mannosyl unit. The chemical shift for C-1 of an a-D-mannosyl linked to 0-2 or 0-3 of another a-D-mannosyl residue resonates at 103.5 p.p.m., whereas that of an a-D-mannosyl residue linked to 0-6 of another a-D-mannosyl unit will resonate at — 100.6 p.p.m. Moreover, if 0-2 of an a-D-mannosyl residue is glycosylated, the chemical shift of C-l of that residue will move —1.5 p.p.m. from its expected position. 

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