Evidence for a Novel O-Linked Sialylated Trisaccharide on Ser-248 of Human Plasminogen 2

• Published in: The Journal of biological chemistry 1997-03, Vol.272 (11), p.7408-7411
• Main Authors: Pirie-Shepherd, Steven R., Stevens, Robert D., Andon, Nancy L., Enghild, Jan J., Pizzo, Salvatore V.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Chromatography, High Pressure Liquid; Glycosylation; Humans; Molecular Sequence Data; Plasminogen - chemistry; Trisaccharides - chemistry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.11.7408

Human plasminogen, the inactive precursor of plasmin, exists in two major glycoforms. Plasminogen 1 contains an N-linked oligosaccharide at Asn-289 and an O-linked oligosaccharide at Thr-345. Plasminogen 2 is known to contain only an O-linked oligosaccharide at Thr-345. However, plasminogen 2 displays a further well documented microheterogeneity dependent on the N-acetylneuraminic acid content, which has functional consequences with regard to activation of plasminogen. The proposed structure and number of known oligosaccharide linkages in plasminogen 2 is insufficient to account for this microheterogeneity. In the present study, a combination of trypsin digestion, lectin affinity chromatography, Edman degradation amino acid sequence analysis, carbohydrate composition analysis, and mass spectrometry revealed the existence of a novel site for O-linked glycosylation on plasminogen 2 at Ser-248. Direct evidence for the structure of the carbohydrate was obtained from a combination of lectin affinity chromatography, desialylation experiments, and mass spectrometry analysis. These findings provide a structural basis for some of the observed microheterogeneity, and have implications with regard to the known functional consequences of the extent of sialylation of plasminogen.