GLYCOSYLATION PATTERN OF HUMAN INTER-ALPHA-INHIBITOR HEAVY-CHAINS

Human inter-alpha-inhibitor (I alpha I) is a plasma serine-proteinase inhibitor. It consists of three polypeptide chains covalently linked b y a glycosaminoglycan chain: a light chain named bikunin carrying the anti-proteinase activity and two heavy chains, H1 and H2, which exhibi t specific properties, e.g. they interact with hyaluronan thus stabili zing the extracellular matrix. In this study, using matrix-assisted la ser desorption ionizatian-time-of-flight MS and amino acid sequencing of tryptic peptides, we provide a detailed analysis of the glycosylati on pattern of both heavy chains. H1 carries two complex-type N-glycans of predominantly biantennary structure linked to asparagine residues at positions 256 and 559 respectively. In contrast, the oligo-sacchari des attached to H2 are a complex-type N-glycan in the N-terminal regio n of the protein (Asn(64)) and three to four type-1 core-structure O-g lycans mono- or di-sialylated, clustered in the C-terminal region. We propose that these O-glycans might function as a recognition signal fo r the H2 heavy chain. The biological implications of this hypothesis, notably for the biosynthetic pathway of I alpha I, are discussed.