A GLYCOSULPHATASE THAT REMOVES SULFATE FROM MUCUS GLYCOPROTEIN

A novel glycosulphatase has been purified from a mucus glycopeptide-degrading Prevotella from the colon. The purified enzyme removed inorganic [S-35]sulphate from S-35-labelled native rat gastric mucus glycoprotein. Desulphation of mucus glycoprotein was initially rapid (19% complete after 10 min) but then plateaued, reaching only 33% after 3 h. Crude periplasmic extracts could remove 79% of the radioactivity as inorganic sulphate. These results suggest that steric hindrance may limit the access of the purified glycosulphatase to the mucus glycoprotein oligosaccharide chains in the absence of glycosidases, and/or that the enzyme may have the wrong specificity for some of the remaining sulphated sugars in the chains. The apparent molecular mass of the enzyme was 111 kDa as judged from gel exclusion chromatography, and it appeared to be composed of two identical subunits. The enzyme was localized in the periplasm of the bacterium, and using pig gastric mucus glycopeptide as a growth substrate markedly increased enzyme levels. Enzymic activity increased at the end of the growth phase. The substrate specificity of the enzyme was tested against low-molecular-mass sulphated molecules. The monosaccharides glucose 6-sulphate and N-acetylglucosamine 6-sulphate were rapidly desulphated, the latter being the major sulphated sugar in some mucus glycoproteins. Lactose 6-sulphate, galactose 6-sulphate, sulphated steroids and unsaturated disaccharide sulphate breakdown products from chondroitin sulphate were not desulphated. Glycosulphatases which can remove sulphate from mucus glycoproteins may play an important role in the degradation of highly sulphated mucus glycoproteins in the digestive tract, and could modify the effectiveness of mucus glycoproteins in mucosal protection.