A 500-MHz proton-magnetic-resonance study of several fragments of the carbohydrate-protein linkage region commonly occurring in proteoglycans

Abstract

The proton-magnetic-resonance spectra of three partial structures of the carbohydrate-protein linkage region that frequently occurs in proteoglycans, namely, beta-d-Galp-(1->3)-beta-d-Galp-(1->4)-beta-d-Xylp-(1->O)-l-Ser, were recorded in 2H2O at 500 MHz; they could be completely interpreted, both for the glyco-serines and for the corresponding glyco-xylitols. The chemical shifts and the coupling constants were refined by computer simulation of the spectra.

The change in the chemical shift of H-4 of a d-galactopyranosyl residue upon substitution at C-3 by a beta-d-galactopyranosyl group is proposed to be characteristic for this particular attachment, making H-4 of galactose a structural-reporter group. The three constituting monosaccharides adopt the 4C1 (d) ring conformation. The terminal galactopyranosyl group and the internal galactopyranosyl residue differ as to the population of rotamers around the C-5/C-6 axis. Concomitantly, the flexibility of their glycosidic linkages is distinct.