Carbohydrate of the human plasminogen variants. III. Structure of the O-glycosidically linked oligosaccharide unit.

The preceding two manuscripts in this issue (Hayes, M. L., and Castellino, F. J. (1979) J. Biol. Chem. 254, 8768-8771, 8772-8776) describe the isolation and characterization of glycopeptides from human plasminogen affinity chromatography variants 1 and 2. Plasminogen variant 1 contains an asparagine288-based branched carbohydrate structure, which has been established in the immediately preceding manuscript. This structure is absent in variant 2. Plasminogen variants 1 and 2 contain a threonine-based glycoconjugate. This latter structure has been established by combination of methylation data, glycosidase digestions, periodate oxidations, and Smith degradations of the beta-eliminated reduced oligosaccharides. One glycopeptide unit, isolated from both plasminogen variants 1 (1D) and 2 (2D) possessed the following structure: Sia alpha 2 yields 3Gal beta 1 yields 3GalNAc-Thr. The threonine was found to be residue 345 in the Glu-plasminogen sequence. Another glycopeptide unit was also found to be present, in lower yields in both variants 1 (1E) and 2 (2E). The structure of this unit was: Sia alpha 2 yields 3Gal beta1 yields 3GalNAc-Thr. : formula: (see text), alpha 2,6 Sia. Again Thr 345 was the glycosylated amino acid. The amino acid sequence around the glycosylated threonine was found to be NH2-Ala.Pro.Thr(CHO).Ala.Pro.Pro.Glu.