title: Characterization of the mutant β-subunit of β-hexosaminidase for dimer formation responsible for the adult form of Sandhoff disease with the motor neuron disease phenotype.
abstract: The adult form of Sandhoff disease with the motor neuron disease phenotype is a rare neurodegenerative disorder caused by mutations in HEXB encoding the β-subunit of β-hexosaminidase, yet the properties of mutant β-subunits of the disease have not been fully determined. We identified a novel mutation (H235Y) in the β-sheet of the (β/α)₈-barrel domain, in addition to the previously reported P417L mutation that causes aberrant splicing, in a Japanese patient with the motor neuron disease phenotype. Enzyme assays, gel filtration studies and immunoprecipitation studies with HEK293 cells transiently expressing mutant β-subunits demonstrated that the H235Y mutation abolished both α-β and β-β dimer formation without increasing β-hexosaminidase activity, whereas other reported mutant β-subunits (Y456S, P504S or R533H) associated with the motor neuron disease phenotype formed dimers. Structural analysis suggested that the H235Y mutation in the β-sheet of the (β/α)₈-barrel domain changed the conformation of the β-subunit by causing a clash with the E288 side chain. In summary, H235Y is the first mutation in the β-sheet of the (β/α)₈-barrel domain of the β-subunit that abolishes α-β and β-β dimer formation; the presented patient is the second patient to exhibit the motor neuron disease phenotype with P417L and a non-functional allele of HEXB.
authors.affiliation: Department of Genetics, Institute for Developmental Research, Aichi Human Service Center, 713-8 Kamiya-cho, Kasugai, Aichi 480-0392, Japan.
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Yamada
authors.forename: Yuhei
authors.initials: Y
authors.lastname: Takado
authors.forename: Yusuke S
authors.initials: YS
authors.lastname: Kato
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Yamada
authors.forename: Hideaki
authors.initials: H
authors.lastname: Ishiguro
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Wakamatsu
mesh_terms: D019943:Amino Acid Substitution; D006801:Humans; D008297:Male; D008875:Middle Aged; D008958:Models, Molecular; D016472:Motor Neuron Disease / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism*; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012497:Sandhoff Disease / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D054821:beta-Hexosaminidase beta Chain / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D050505:Mutant Proteins; D011994:Recombinant Proteins; C513386:HEXB protein, human; D054821:beta-Hexosaminidase beta Chain