Carbohydrate structure of human fibrinogen. Use of 300-MHz 1H-NMR to characterize glycosidase-treated glycopeptides

The carbohydrate composition of fibrinogen and constituent S-carboxymethylated chains was determined. All the carbohydrate on the parent molecule could be accounted for on the B beta and gamma chains. The A alpha chain was found to be devoid of carbohydrate. Glycopeptides were prepared from fibrinogen, B beta, and gamma chains by pronase digestion and subsequent chromatography on Sephadex G-50. The 300-MHz 1H-NMR spectra of glycopeptides from all three sources were consistent with biantennary type oligosaccharide chains. The glycopeptides resulting from exoglycosidase digestions were examined with 300-MHz 1H-NMR spectroscopy, and the changes in the signals caused by selective removal of sugar residues were studied. This technique enabled us to assign each anomeric proton to the corresponding monosaccharide unit independent of previous work. Our results indicate that fibrinogen glycopeptides are of the biantennary type, and are in complete agreement with the previously reported peak assignments (Vliegenthart, J. F. G., van Halbeek, H., and Dorland, L. (1981) Pure Appl. Chemn. 53, 45-77). Affinity chromatography of the glycopeptides on concanavalin A-Sepharose also showed that the glycopeptides from fibrinogen are greater than 95% biantennary oligosaccharide chains. Based on carbohydrate composition, 1H-NMR spectroscopy, sequential exoglycosidase digestion, and gas chromatography-mass spectrometry of derived partially methylated alditol acetates, we propose that fibrinogen contains four oligosaccharide chains of the structure shown below. (formula, see text)