Association of N-acetylgalactosamine-6-sulfate sulfatase with the multienzyme lysosomal complex of beta-galactosidase, cathepsin A, and neuraminidase. Possible implication for intralysosomal catabolism of keratan sulfate.
N-Acetylgalactosamine-6-sulfate sulfatase (GALNS) catalyzes the first step of intralysosomal keratan sulfate (KS) catabolism. In Morquio type A syndrome GALNS deficiency causes the accumulation of KS in tissues and results in generalized skeletal dysplasia in affected patients. We show that in normal cells GALNS is in a 1.27-MDa complex with three other lysosomal hydrolases: beta-galactosidase, alpha-neuraminidase, and cathepsin A (protective protein). GALNS copurifies with the complex by different chromatography techniques: affinity chromatography on both cathepsin A-binding and beta-galactosidase-binding columns, gel filtration, and chromatofocusing. Anti-human cathepsin A rabbit antiserum coprecipitates GALNS together with cathepsin A, beta-galactosidase, and alpha-neuraminidase in both a purified preparation of the 1. 27-MDa complex and crude glycoprotein fraction from human placenta extract. Gel filtration analysis of fibroblast extracts of patients deficient in either beta-galactosidase (beta-galactosidosis) or cathepsin A (galactosialidosis), which accumulate KS, demonstrates that the 1.27-MDa complex is disrupted and that GALNS is present only in free homodimeric form. The GALNS activity and cross-reacting material are reduced in the fibroblasts of patients affected with galactosialidosis, indicating that the complex with cathepsin A may protect GALNS in the lysosome. We suggest that the 1.27-MDa complex of lysosomal hydrolases is essential for KS catabolism and that the disruption of this complex may be responsible for the KS accumulation in beta-galactosidosis and galactosialidosis patients.
Service de Génétique Médicale, Hôpital Sainte-Justine, Montréal, Québec, Canada H3T 1C5. alex@justine.umontreal.ca
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D000818:Animals; D002268:Carboxypeptidases / Q000378:metabolism*; D043402:Cathepsin A; D002811:Chondroitinsulfatases / Q000378:metabolism*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007525:Isoelectric Focusing; D007632:Keratan Sulfate / Q000378:metabolism*; D008247:Lysosomes / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009439:Neuraminidase / Q000378:metabolism*; D010920:Placenta / Q000201:enzymology; D011817:Rabbits; D001616:beta-Galactosidase / Q000378:metabolism*
D009097:Multienzyme Complexes; D007632:Keratan Sulfate; D002811:Chondroitinsulfatases; C102295:GALNS protein, human; D009439:Neuraminidase; D001616:beta-Galactosidase; D002268:Carboxypeptidases; C468629:CTSA protein, human; D043402:Cathepsin A