Two allelic forms of human arylsulfatase A with different numbers of asparagine-linked oligosaccharides.

The biosynthesis of arylsulfatase A in human skin fibroblasts was studied by labeling cells and isolating arylsulfatase A using immune precipitation and polyacrylamide gel electrophoresis under denaturing and reducing conditions. Arylsulfatase A was synthesized as precursor polypeptides of 62 kDa or 59.5 kDa. Cell lines synthesizing either or both polypeptides were found. The results of a family study were consistent with the assumption that the two arylsulfatase A polypeptides are of allelic nature. In various heterozygous cell lines, the two polypeptides were formed at equal or different rates. The relative rate of biosynthesis was constant for an individual cell line, suggesting that both allelic products were under separate genetic control. In a group of 21 unrelated individuals, the gene frequency of alleles for the 62- and 59.5-kDa precursor forms was 3:1. The two allelic forms of the arylsulfatase A polypeptides were converted into a 57-kDa form by endo-beta-N-acetylglucosaminidase H, an enzyme specifically removing asparagine-linked oligosaccharides of the high-mannose (and hybrid) type. The apparent difference in the number of asparagine-linked oligosaccharides suggests that the two allelic genes differ in a region coding the sequence Asn-X-Thr(Ser), which is required for attachment of asparagine-linked oligosaccharides.