title: Characterization of two Turkish beta-hexosaminidase mutations causing Tay-Sachs disease.
abstract: Two homoallelic mutations have recently been identified in the alpha-subunit of hexosaminidase A (EC 3.2.1.52) causing the infantile form of Tay-Sachs disease in Turkish patients. Both of these mutations, a 12 bp deletion (1096-1107 or 1098-1108 or 1099-1109) in exon 10 and a point mutation (G1362 to A, Gly454 to Asp) in exon 12, are located in the catalytic domain of the hexosaminidase alpha-chain. In order to determine whether these mutations affect the function of the catalytic domain or result in an instable protein, both mutant cDNAs were overexpressed in COS-1 cells. As judged by Western blotting, transfections of wild-type cDNA produced pro-alpha-chain and mature alpha-chain in parallel with a fivefold increase in cellular hexosaminidase activity using the synthetic substrate 4-methylumbelliferyl beta-N-acetylglucosamine 6-sulfate (MUGS). However, both mutants produced only pro-alpha-chains, although no mature form or detectable hexosaminidase activity towards two different synthetic substrates was observed. These data are consistent with the biochemical phenotype of infantile Tay-Sachs disease. We conclude that the overexpressed mutant pro-alpha-chains were misfolded and could not undergo further proteolytic processing to the active form of the enzyme in the lysosome.
authors.affiliation: Department of Biochemistry, Hacettepe University Faculty of Medicine, 06100 Ankara, Turkey. ozkara@ato.org.tu
authors.forename: Hatice Asuman
authors.initials: HA
authors.lastname: Ozkara
authors.forename: Konrad
authors.initials: K
authors.lastname: Sandhoff
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D004252:DNA Mutational Analysis; D018076:DNA, Complementary / Q000235:genetics; D054818:Hexosaminidase A; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010641:Phenotype; D017510:Protein Folding; D013661:Tay-Sachs Disease / Q000201:enzymology / Q000208:ethnology / Q000235:genetics*; D014162:Transfection; D014421:Turkey / Q000208:ethnology; D001619:beta-N-Acetylhexosaminidases / Q000737:chemistry / Q000235:genetics*
chemical_list: D018076:DNA, Complementary; D054818:Hexosaminidase A; D001619:beta-N-Acetylhexosaminidases