Abstract
We have previously described the kinetics of association of the alpha- and beta-subunits of beta-hexosaminidase A in intact cultured human fibroblasts, using biosynthetic labeling and immunoprecipitation with antisera that distinguish between monomeric and associated alpha-chains (Proia, R. L., d'Azzo, A., and Neufeld, E. F. (1984) J. Biol. Chem. 259, 3350-3354). We now show lack of alpha-beta association in fibroblasts of several individuals deficient in beta-hexosaminidase A (5 patients with nonclassic forms of Tay-Sachs disease and 2 asymptomatic siblings). Defective association was accompanied by markedly reduced (less than one-tenth of normal) conversion of the alpha-chain precursor of Mr = 67,000 to the mature lysosomal form of Mr = 54,000. Analysis by hybridization with fibroblasts lacking the alpha- or beta-chain showed that the association defect resided in the alpha-chain. Most of the cell strains studied also had decreased synthesis of the alpha-chain, suggesting compound heterozygosity with the Ashkenazi Tay-Sachs (no synthesis) allele. An unusual feature of the association defect is the variability in the resulting clinical manifestations, even within families, implying that other factors determine the adequacy of the residual associated beta-hexosaminidase A in vivo.
Highlights
From the $Genetics and Biochemistry Branch, National Instituteof Arthritis, Diabetes,and Digestive and Kidney Diseases, Bethesda, Maryland 20205, the §Eunice Kennedy Shriver Center for Mental Retardation, Walthnm, Massachusetts 02154,and the 11Division of Medical Genetics, HarborlUCLAMedical Center, Torrance,California 90509
Analysis defect is in theA isozyme (Tay-Sachs disease, known as by hybridization with fibroblasts lacking the a- or j3- the B variant of GMZgangliosidosis),in bothA and B isozymes chain showed that the association defect resided in the (Sandhoff disease or 0 variant), or in the activator protein u-chain
An unusual feature of the association bothTay-Sachs disease andSandhoff diseaserangesfrom defect is the variability in the resulting clinical manifestations, even within families, implying that other factors determine the adequacy of the residual associated &hexosaminidase A in vivo
Summary
From the $Genetics and Biochemistry Branch, National Instituteof Arthritis, Diabetes,and Digestive and Kidney Diseases, Bethesda, Maryland 20205, the §Eunice Kennedy Shriver Center for Mental Retardation, Walthnm, Massachusetts 02154,and the 11Division of Medical Genetics, HarborlUCLAMedical Center, Torrance,California 90509. Like ation of the a- and #?-subunitsof @-hexosaminidaseA other lysosomal enzymes, P-hexosaminidase is synthesized in in intact cultured human fibroblasts, using biosyn- precursor form and undergoes many post-translational modthetic labeling and immunoprecipitation with antisera ificationsincludingglycosylation,oligosaccharide phosphothat distinguish between monomeric and associated achains(Proia, R. We show lack of a-8 association in fibroblasts of several individuals deficient in &hexosaminidase A (5 patients with nonclassic forms of Tay-Sachs disease and 2 asymptomatic siblings). Analysis defect is in theA isozyme (Tay-Sachs disease, known as by hybridization with fibroblasts lacking the a- or j3- the B variant of GMZgangliosidosis),in bothA and B isozymes chain showed that the association defect resided in the (Sandhoff disease or 0 variant), or in the activator protein u-chain. An unusual feature of the association bothTay-Sachs disease andSandhoff diseaserangesfrom defect is the variability in the resulting clinical manifestations, even within families, implying that other factors determine the adequacy of the residual associated &hexosaminidase A in vivo. Itstwo genetically distinct chains,a and p, can associate to give isozymes of different structure and catalytic activity. p-Hexosaminidase A, or a-p, hydrolyzes many natural and syntheticP-N-acetylglucosaminides and 0-
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