title: Zinc transporters, ZnT5 and ZnT7, are required for the activation of alkaline phosphatases, zinc-requiring enzymes that are glycosylphosphatidylinositol-anchored to the cytoplasmic membrane.
abstract: Numerous proteins are properly folded by binding with zinc during their itinerary in the biosynthetic-secretory pathway. Several transporters have been implicated in the zinc entry into secretory compartments from cytosol, but their precise roles are poorly understood. We report here that two zinc transporters (ZnT5 and ZnT7) localized in the secretory apparatus are responsible for loading zinc to alkaline phosphatases (ALPs) that are glycosylphosphatidylinositol-anchored membrane proteins exposed to the extracellular site. Disruption of the ZnT5 gene in DT40 cells decreased the ALP activity to 45% of that in the wild-type cells. Disruption of the ZnT7 gene lowered the ALP activity only by 20%. Disruption of both genes markedly decreased the ALP activity to <5%. Overexpression of human ZnT5 or ZnT7 in DT40 cells deficient in both ZnT5 and ZnT7 genes recovered the ALP activity to the level comparable to that in the wild-type cells. The inactive ALP protein in DT40 cells deficient in both ZnT5 and ZnT7 genes was transported to cytoplasmic membrane like the active ALP protein in the wild-type cells. Thus both ZnT5 and ZnT7 contribute to the conversion of apo-ALP to holo-ALP.
authors.affiliation: Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Suzuki
authors.forename: Kaori
authors.initials: K
authors.lastname: Ishihara
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Migaki
authors.forename: Wataru
authors.initials: W
authors.lastname: Matsuura
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kohda
authors.forename: Katsuzumi
authors.initials: K
authors.lastname: Okumura
authors.forename: Masaya
authors.initials: M
authors.lastname: Nagao
authors.forename: Yuko
authors.initials: Y
authors.lastname: Yamaguchi-Iwai
authors.forename: Taiho
authors.initials: T
authors.lastname: Kambe
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D015032:Zinc / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D000469:Alkaline Phosphatase; D015032:Zinc