Structure of the Linkage-Region between Polysaccharide Chain and Core Protein in Bovine Corneal Proteokeratan Sulfate

Abstract

Peptidokeratan sulfate from bovine cornea was degraded by a combination of desulfation, exoenzymic digestion and finally digestion with endo-.beta.-N-acetylglucosaminidase D. The same procedure was carried out both with [3H]fucose-labeled and [3H]mannose-labeled peptidokeratan sulfate. Data obtained by methylation analysis of peptidokeratan at the different degradation steps, as well as action of endo-.beta.-N-acetylglucosaminidase D, showed that the binding-region in proteokeratan sulfate from bovine cornea is identical with a structure found in various GlcNAc(.beta.1-N)-Asn-linked mannosyl glycoproteins. The existence of a chitobiose unit between asparagine and mannose was proved by action of endo-.beta.-N-acetylglucosaminidase D. The existence and position of an (.alpha.1 .fwdarw. 6)-linked fucosyl residue at the Asn-bound GlcNAc was demonstrated by action of .alpha.-fucosidase, endo-.beta.-N-acetylglucosaminidase D and by gel chromatography on Bio-Gel P-4. By gas chromatography/mass spectrometry studies, the existence of a 1,4,6-trisubstituted beside a 1,4-disubstituted GlcNAc in the binding-region oligosaccharide was shown. Other results reported are according to analytical data previously published (Keller et al., 1981).