600 MHz NMR studies of human articular cartilage keratan sulfates

The use of high-field two-dimensional 1H-correlation data is described for the detailed comparison of intact keratan sulfate polymer chains derived from human articular cartilage sources as a function of age. For fetal material the nonreducing chain termini are shown to be sparsely capped by sialyl groups which, if present, are exclusively (alpha2-3)-linked to an unsulfated galactose residue. The asialo capping segment has the structure: Gal-GlcNAc6S-Gal-GlcNAc6S-. Examination of keratan sulfate from 10-year-old cartilage shows that capping by sialyl groups is complete, with (alpha2-3)-linkages predominant; for both this and the 38-year-old cartilage the three capping structures: NeuAc(alpha2-3)-Gal-GlcNAc6S-Gal-GlcNAc6S-, NeuAc(alpha2-3)-Gal-GlcNAc6S-Gal6S-GlcNAc6S-, and NeuAc(alpha2-3)-Gal6S-GlcNAc6S-Gal6S-GlcNAc6S- are clearly recognizable. The level of (alpha2-6)-linked chain capping sialyl groups is significant for 38-year-old cartilage keratan sulfate. Structural information concerning the linkage region to protein and the distribution of galactose environments is readily obtained from the spectra. Signal complexities severely limit the usefulness of two-dimensional correlation spectroscopy at 600 MHz for the examination of N-acetylglucosamine residues within the poly(N-acetyllactosamine) repeat sequence and signals representing fucose placements remain undifferentiated. This nondestructive approach complements current degradative methods for the structural examination of keratan sulfates.