title: Molecular defect of tissue-nonspecific alkaline phosphatase bearing a substitution at position 426 associated with hypophosphatasia.
abstract: Mutations in the ALPL gene encoding tissue-nonspecific alkaline phosphatase (TNSALP) cause hypophosphatasia (HPP), a genetic disorder characterized by deficiency of serum ALP and hypomineralization of bone and teeth. Three missense mutations for glycine 426 (by standard nomenclature) of TNSALP have been reported: cysteine (p.G426C), serine (p.G426S), and aspartate (p.G426D). We expressed TNSALP mutants carrying each missense mutation in mammalian cells. All three TNSALP mutants appeared on the cell surface like the wild-type (WT) TNSALP, although the cells expressing each TNSALP mutant exhibited markedly reduced ALP activity. TNSALP (WT) was mainly present as a 140 kDa catalytically active dimeric form, whereas ~80 kDa monomers were the predominant molecular species in the cells expressing TNSALP (p.G426D) or TNSALP (p.G426S), suggesting that aspartate or serine at position 426 may hamper the subunit assembly essential for the enzymatic function of TNSALP. Alternatively, the subunits of TNSALP (p.G426C) were found to be aberrantly cross-linked by disulfide bonds, giving rise to a 200 kDa form lacking ALP activity. Taken together, our results reveal that the amino acid substitutions at position 426 of TNSALP differentially affect the structure and function of TNSALP, leading to understanding of the molecular and cellular basis of HPP.
authors.affiliation: , 3-22 Heiman Street, Kitchener, ON, N2M 3L6, Canada.
authors.forename: Hiba A
authors.initials: HA
authors.lastname: Al-Shawafi
authors.affiliation: Kitasato Junior College of Health and Hygienic Sciences, 500 Kurotsuchi-Shinden, Minami-Uonuma, Niigata, 949-7241, Japan. komaru.k@kitasato-u.ac.jp.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Komaru
authors.affiliation: Division of Oral Biochemistry, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.|Showa Hospital, 911-1 Tokunaga Omachi, Nishi-ku, Fukuoka, 819-0375, Japan.
authors.forename: Kimimitsu
authors.initials: K
authors.lastname: Oda
mesh_terms: D000469:Alkaline Phosphatase / Q000737:chemistry / Q000235:genetics; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D006801:Humans; D007014:Hypophosphatasia / Q000201:enzymology / Q000235:genetics; D020125:Mutation, Missense; D000072417:Protein Domains; D013329:Structure-Activity Relationship
chemical_list: C548267:ALPL protein, human; D000469:Alkaline Phosphatase
keywords: Cross-linking; Dimerization; Disulfide bond; Genetic disorder; Hypophosphatasia; Tissue-nonspecific alkaline phosphatase