Synthesis and processing of alpha-galactosidase A in human fibroblasts. Evidence for different mutations in Fabry disease.
The synthesis and processing of the human lysosomal enzyme alpha-galactosidase A was examined in normal and Fabry fibroblasts. In normal cells, alpha-galactosidase A was synthesized as an Mr = 50,500 precursor, which contained phosphate groups in oligosaccharide chains cleavable by endoglucosaminidase H. The precursor was processed via ill-defined intermediates to a mature Mr 46,000 form. Processing was complete within 3-7 days after synthesis. In the presence of NH4Cl and in I-cell fibroblasts, the majority of newly synthesized alpha-galactosidase A was secreted as an Mr = 52,000 form. For comparison, the processing and stability of alpha-galactosidase A were examined in fibroblasts from five unrelated patients with Fabry disease, which is caused by deficient alpha-galactosidase A activity. In one cell line, synthesis of immunologically cross-reacting polypeptides was not detectable. In another, the synthesis, processing, and stability of alpha-galactosidase A was indistinguishable from that in normal fibroblasts. In a third Fabry cell line, the mutation retarded the maturation of alpha-galactosidase A. Finally, in two cell lines, alpha-galactosidase A polypeptides were synthesized that were rapidly degraded following delivery to lysosomes. These results clearly indicate that Fabry disease comprises a heterogeneous group of mutations affecting synthesis, processing, and stability of alpha-galactosidase A.
D000643:Ammonium Chloride / Q000494:pharmacology; D002460:Cell Line; D003429:Cross Reactions; D000795:Fabry Disease / Q000201:enzymology* / Q000235:genetics; D005347:Fibroblasts / Q000201:enzymology*; D005696:Galactosidases / Q000378:metabolism*; D006596:Hexosaminidases / Q000378:metabolism; D006801:Humans; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D008970:Molecular Weight; D009154:Mutation; D000519:alpha-Galactosidase / Q000235:genetics / Q000378:metabolism*
D000643:Ammonium Chloride; D005696:Galactosidases; D006596:Hexosaminidases; D000519:alpha-Galactosidase; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase