New pathway of heparan sulphate degradation: Iduronate sulphatase and N-sulphoglucosamine 6-sulphatase act on the polymer chain prior to depolymerisation by a N-sulpho-glucosaminidase and glycuronidases in the mollusc Tagelus gibbus

It has previously been shown that in the mollusc Anomalocardia brasiliana the desulphation of chondroitin sulphate precedes its depolymerisation by β-glucuronidase and β- N-acetylgalactosaminidase (Sousa Jr. et al. J. Biol. Chem. 1990;265:20150–20155). This led us to investigate whether in molluscs, sulphatases also act on heparan sulphate before its depolymerisation by glycosidases. Radioactively labelled [ 35S]heparan sulphate was extensively degraded by enzyme extracts prepared from the mollusc Tagelus gibbus. Several enzymes acting in concert degrade the compound to inorganic sulphate, glucosamine N-sulphate, N-acetylglucosamine-6 sulphate and other oligosaccharide products. These results indicate the presence of iduronate sulphatase, N-sulphoglucosamine 6-sulphatase α- N-sulphoglucosaminidase, β-glucuronidase and α- l-iduronidase. The di- and mono-saccharide composition of the oligosaccharides were analysed with the aid of heparitinase II from Flavobacterium heparinum. These analyses led to the characterisation of two sulphatases that act on the polymer chain removing sulphates from the C-2 position of iduronic acid residues and the C-6 position of the glucosamine moieties, respectively. The different enzymes were partially fractionated by ion exchange chromatography and molecular sieving. These results led to the proposition of a new pathway of degradation of heparan sulphate where sulphatases act directly on the polymer chain which is then depolymerised by several glycosidases.