Carbohydrate Chains and Their Binding Sites in Mistletoe Lectin I

The carbohydrate moieties, linked to mistletoe lectin 1 (ML-1) are characterized by enzymatic digestion of the individual A and B chains (MLA and MLB), HPLC separation of the (glyco)peptide digests and their sequence and mass spectrometric analysis. All carbohydrate chains are linked via Asn residues to the MLA protein molecule. A xylomannose-type oligosaccharide (1) structure (Man3Xyl1Fuc1GlcNac2) is attached to the Asn112 residue of the A chain. Three different glycosylation sites are identified for the B chain: oligosaccharide II (Man6GlcNac2) is found to be linked to Asn96 as well as Asn136 residues. In homologous mistletoe lectins, isolated from different harvest batches, oligosaccharide III (Man5GlcNac2) is attached to Asn136 instead of oligosaccharide II**.