RECEPTOR-MEDIATED BINDING OF 2 GLYCOSYLATION FORMS OF N-ACETYLGALACTOSAMINE-4-SULFATASE

The lysosomal storage disorders are a group of inherited metabolic dis eases each characterised by a relative or absolute deficiency of one o r more of the lysosomal proteins involved in the hydrolysis of glycoco njugates or in the transport of the resulting product. Enzyme replacem ent therapies are under consideration for a number of these disorders and are based on the in vitro observation that cells from affected pat ients can be corrected by addition of exogenous enzyme. In this study, two glycosylation variants of the lysosomal enzyme N-acetylgalactosam ine-4-sulphatase (45) (the deficiency of which causes Mucopolysacchari dosis (MPS) type VI, (Maroteaux-Lamy syndrome) were made by expression of 45 cDNA in both wild type chinese hamster ovary (CHO-K1), and Led (N-acetylglucosaminyltransferase I deficient CHO-K1) cells. Difference s in the glycosylation pattern of the two enzyme forms were demonstrat ed with endoglycosidase H and N-glycosidase F digestions. The receptor mediated binding of these two forms of 45 to two cell types, human sk in fibroblasts and rat alveolar macrophages, was then analysed. We hav e shown that both enzyme forms bind to the mannose-6-phosphate recepto r on human skin fibroblasts with equal affinity demonstrating that the degree of phosphorylation of mannose residues in the two forms is sim ilar. However, using rat alveolar macrophages, we found that the bindi ng/uptake of the two enzymes differs considerably. These results show that differences in glycosylation of lysosomal enzymes can be an impor tant factor in altering enzyme uptake by different cell types. Thus, p roducing carbohydrate modification variants in this way may be useful for altering the distribution of exogenous enzyme in vivo. (C) 1998 El sevier Science B.V. All rights reserved.