title: Isolation and functional characterization of Ca2+/H+ antiporters from cyanobacteria.
abstract: Genome sequences of cyanobacteria, Synechocystis sp. PCC 6803, Anabaena sp. PCC 7120, and Thermosynechococcus elongatus BP-1 revealed the presence of a single Ca2+/H+ antiporter in these organisms. Here, we isolated the putative Ca2+/H+ antiporter gene from Synechocystis sp. PCC 6803 (synCAX) as well as a homologous gene from a halotolerant cyanobacterium Aphanothece halophytica (apCAX). In contrast to plant vacuolar CAXs, the full-length apCAX and synCAX genes complemented the Ca2+-sensitive phenotype of an Escherichia coli mutant. ApCAX and SynCAX proteins catalyzed specifically the Ca2+/H+ exchange reaction at alkaline pH. Immunological analysis suggested their localization in plasma membranes. The Synechocystis sp. PCC 6803 cells disrupted of synCAX exhibited lower Ca2+ efflux activity and a salt-sensitive phenotype. Overexpression of ApCAX and SynCAX enhanced the salt tolerance of Synechococcus sp. PCC 7942 cells. Mutagenesis analyses indicate the importance of two conserved acidic amino acid residues, Glu-74 and Glu-324, in the transmembrane segments for the exchange activity. These results clearly indicate that cyanobacteria contain a Ca2+/H+ antiporter in their plasma membranes, which plays an important role for salt tolerance.
authors.affiliation: Research Institute, Meijo University, Nagoya, 468-8502, Japan.
authors.forename: Rungaroon
authors.initials: R
authors.lastname: Waditee
authors.forename: Gazi Sakir
authors.initials: GS
authors.lastname: Hossain
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Tatsunosuke
authors.initials: T
authors.lastname: Nakamura
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Shikata
authors.forename: Jun
authors.initials: J
authors.lastname: Takano
authors.forename: Tetsuko
authors.initials: T
authors.lastname: Takabe
authors.forename: Teruhiro
authors.initials: T
authors.lastname: Takabe
mesh_terms: D000595:Amino Acid Sequence; D017033:Anabaena / Q000235:genetics / Q000378:metabolism; D017920:Antiporters / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D001483:Base Sequence; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010641:Phenotype; D010802:Phylogeny; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride / Q000494:pharmacology; D013045:Species Specificity
chemical_list: D017920:Antiporters; D001426:Bacterial Proteins; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D004269:DNA, Bacterial; D011994:Recombinant Proteins; C027614:calcium-hydrogen antiporters; D012965:Sodium Chloride