A comparative study of the N-linked oligosaccharide structures of human IgG subclass proteins

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Abstract
Quantitative oligosaccharide profiles were determined for each of 18 human IgG paraproteins representing the four subclasses. Each paraprotein exhibits a unique profile that may be substantially different from that observed for polyclonal IgG. The IgG2 and some IgG3 proteins analysed exhibit a predominance of oligosaccharide moieties having galactose on the Man(.alpha.1.fwdarw.3) arm rather than the Man(.alpha.1.fwdarw.6) arm; it was previously held that galactosylation of the Man(.alpha.1.fwdarw.6) arm is preferred, as observed for IgG1, IgG4 and polyclonal IgG. An IgG4 protein is reported that has galactosylated Man(.alpha.1.fwdarw.3) and Man(.alpha.1.fwdarw.6) arms on both Fc-localized carbohydrate moieties; previous findings suggested that such fully glycosylated structures could not be accommodated within the internal space of the C.gamma.2 domains. Unusual monoantennary oligosaccharides present in IgG2 and IgG3 proteins were isolated and their structures determined.