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 (HS) catabolism. In Morquio typ e A syndrome GALNS deficiency causes the accumulation of HS in tissues and results in generalized skeletal dysplasia in affected patients. W e show that in normal cells GALNS is in a 1.27 MDa complex with three other lysosomal hydrolases: beta-galactosidase, alpha-neuraminidase, a nd cathepsin A (protective protein). GALNS copurifies with the complex by different chromatography techniques: affinity chromatography on bo th cathepsin A-binding and beta-galactosidase-binding columns, gel fil tration, and chromatofocusing. Anti-human cathepsin A rabbit antiserum coprecipitates GALNS together with cathepsin A, beta-galactosidase, a nd Lu-neuraminidase in both a purified preparation of the 1.27-MDa com plex and crude glycoprotein fraction from human placenta extract. Gel filtration analysis of fibroblast extracts of patients deficient in ei ther beta-galactosidase (beta-galactosidosis) or cathepsin A (galactos ialidosis), which accumulate KS, demonstrates that the 1.27-MDa comple x is disrupted and that GALNS is present only in free homodimeric form . The GALNS activity and cross-reacting material are reduced in the fi broblasts of patients affected with galactosialidosis, indicating that the complex with cathepsin A may protect GALNS in the lysosome. We su ggest that the 1.27-MDa complex of lysosomal hydrolases is essential f or RS catabolism and that the disruption of this complex may be respon sible for the KS accumulation in beta-galactosidosis and galactosialid osis patients.