Expression of heparan sulphate L-iduronyl 2-O-sulphotransferase in human kidney 293 cells results in increased D-glucuronyl 2-O-sulphation

Functionally important interactions between heparan sulphate and a variety of proteins depend on the precise location of O-sulphate groups. Such residues occur at C-2 of L-iduronic (IdoA) and D-glucuronic acid (GlcA) units, and at C-3 and C-6 of D-glucosamine (GlcN) units. Stable transfection of human embryonic kidney 293 cells with a cDNA encoding mouse mastocytoma IdoA 2-O-sulphotransferase resulted in an approx. 6-fold increase in O-sulphotransferase activity, compared with control cells, as determined using O-desulphated heparin as an acceptor. Structural analysis of endogenous heparan sulphate in the transfected cells, following metabolic labelling with either [H-3]GlcN or [S-35]sulphate, showed appreciable formation of -GlcA(2-OSO3)-GlcNSO(3)- disaccharide units (6% of total disaccharide units; 17% of total O-sulphated disaccharide units) that were essentially absent from heparan sulphate from control cells. The increase in GlcA 2-O-sulphation was accompanied by a decrease in the amount of IdoA formed, whereas overall 2-O-sulphation or 6-O-sulphation remained largely unaffected. These findings indicate that 2-O-sulphation of IdoA and GlcA residues is catalysed by the same enzyme in heparan sulphate biosynthesis.