Characterization of the oligosaccharides from the invariant chain associated with murine Ia antigens

The oligosaccharide side chains of the murine invariant chain (I(i)) glycoprotein associated with the Ia antigens have been characterized. Affinity chromatography using a monoclonal antibody column was employed to purify the I-A(k) antigen from lysates of the AKTB-1b B cell lymphoma. The invariant chain isolated by this procedure was subsequently digested with proteases, and the resulting glycopeptides were fractionated by reverse-phase high-pressure liquid chromatography (HPLC). The invariant chain appears to contain two glycosylation sites, both of which carry high-mannose oligosaccharides, each with a restricted size distribution and an average composition of Man₆GIcNAc₂ as judged by gel filtration and α-mannosidase digestion. These data, together with the observation that the invariant chain cannot be labeled metabolically with ³H-glucosamine, ³H-fucose, or ³H-galactose, allow the conclusion that the murine invariant chain does not contain complex oligosaccharides and is not O-glycosylated during its association with the Ia antigens.