Human Corneal Keratan Sulfates

The keratan sulfate-containing proteoglycans were isolated from fourteen pooled human corneas (thirteen from 61- to 86-year-olds, plus one from a 12-year-old). These proteoglycans were subjected to digestion with the enzyme keratanase II, and the released oligosaccharides, which included nonreducing termini and repeat region oligosaccharides but not linkage regions, were reduced with alkaline borohydride and identified on two separate ion-exchange columns. Both of the latter had been calibrated with samples, most of which had been derived from bovine corneal keratan sulfate (Tai, G.-H., Huckerby, T. N., and Nieduszynski, I. A. (1996) J. Biol. Chem. 271, 23535-23546) and all of which had been fully characterized by NMR spectroscopic analysis. The capping structures identified in human corneal keratan sulfates occurred in the relative proportions: NeuAcalpha(2-6)- >NeuAcalpha(2-3)- >GalNAc(S)beta(1-3)-. The other groups of capping structures which had been identified in bovine corneal keratan sulfate, i.e. NeuGcalpha(2-3)-, NeuGcalpha(2-6)-, GlcNAc(S)beta(1-3)- were absent, although the possibility of the presence of some Galalpha(1-3)- structures could not be excluded. In addition, the human sample showed significantly higher levels of alpha(1-3)-fucosylated repeat region structures than did the bovine sample, and it is not clear whether this reflects a species or age dependence as the bovine corneas were from young animals, whereas the human corneas were predominantly from an older group. The charge densities and keratan sulfate chain sizes of the human and bovine keratan sulfate-containing proteoglycans were seen to be similar.