Sulphation heterogeneity in the trisaccharide (GalNAcSβ1,4GlcAβ1,3GalNAcS) isolated from the non-reducing terminal of human aggrecan chondroitin sulphate

We report here the isolation and sulphation isomer analyses of trisaccharides GalNAcS(β1,4)GlcA(β1,3)GalNAcS (in which S indicates sulphate) derived from the non-reducing termini of aggrecan chondroitin sulphate. Rat chondrosarcoma and human aggrecans were digested for 1 h at 37 °C with 30 μ-units of endo-chondroitinase ABC per μg of chondroitin sulphate, and trisaccharides were isolated from the digests by ToyoPearl HW40S gel-filtration chromatography. Four trisaccharide species were identified; their sulphation isomer compositions, as determined by digestion with chondroitinase ACII and fluorescence-based ion-exchange HPLC, were GalNAc4Sβ1,4GlcAβ1,3GalNAc4S, GalNAc4Sβ1,4GlcAβ1,3GalNAc6S, GalNAc4,6Sβ1,4GlcAβ1,3GalNAc4S and GalNAc4,6Sβ1,4GlcAβ1,3GalNAc6S. The abundances of such sequences in chondroitin sulphate on aggrecan from normal (foetal to 72 years of age) and from osteoarthritic human knee cartilages were also established. The results showed that non-reducing terminal GalNAc4S or GalNAc4,6S can be linked to either a 4-sulphated or a 6-sulphated disaccharide, suggesting that the sulphation of the last disaccharide might not have a direct effect on the specificity of chondroitin sulphate terminal GalNAc sulphotransferases. Furthermore, for each aggrecan preparation examined, the 4S-to-6S ratio of all chain interior disaccharides was equivalent to that in the last repeating disaccharides at the non-reducing terminus, suggesting that neither chondroitin 4-sulphotransferase nor chondroitin 6-sulphotransferase shows preferential activity near the chain terminus.