Variations in oligosaccharide-protein interactions in immunoglobulin G determine the site-specific glycosylation profiles and modulate the dynamic motion of the Fc oligosaccharides

The present study reports data on the site-specific glycosylation of human IgG. The structures of a series of biantennary complex carbohydrates isolated from IgG were determined by HPLC and mass spectrometry. Differences were found in the structures and occurrences of the carbohydrates in Fab and Fc regions. Carbohydrates from the IgG of RA patients were shown to have a higher degree of truncation relative to carbohydrates from normal serum IgG. Differences in the mobilities of truncated oligosaccharides versus those with a 1,6-arm galactose residue were demonstrated using NMR relaxation measurements. The mobility differences of the carbohydrates are discussed in terms of specific carbohydrate-protein interactions, and the possible molecular basis for RA and other diseases involving Fc glycosylation deficiencies.