Biosynthesis of heparan sulfate. Coordination of polymer-modification reactions in a Chinese hamster ovary cell mutant defective in N-sulfotransferase.

A previous study identified a Chinese hamster ovary cell mutant, pgsE-606, which is defective in the N-sulfotransferase that catalyzes one of the initial polymer-modification reactions in the biosynthesis of heparan sulfate (Bame, K. J., and Esko, J. D. (1989) J. Biol. Chem. 264, 8059-8065). The structure of heparan sulfate generated by these cells reflects a 3-5-fold reduction in enzyme activity. The mutant produces heparan sulfate with half the content of N-sulfated glucosamine residues of that produced by wild-type cells and a more sparse distribution of N-sulfated residues. The present study demonstrates corresponding reductions in the proportion of 6-O-sulfated glucosamine residues (41% reduction) and the content of L-iduronic acid (51% reduction). The amount of 2-O-sulfated L-iduronic acid declines more dramatically (from 25% of total L-iduronic acid in the wild type to 8.4% in the mutant). Enzymatic assay of mixed O-sulfotransferases showed that the mutant has more activity than the wild type. Previous studies on the biosynthesis of heparin/heparan sulfate in cell-free systems point to a pivotal role of N-sulfation in determining the extent of the subsequent polymer-modification reactions. The present study shows that this concept also applies to heparan sulfate biosynthesis in the intact cell.