title: Sodium-dependent uptake of glutamate by novel ApGltS enhanced growth under salt stress of halotolerant cyanobacterium Aphanothece halophytica.
abstract: Glutamate is a major free amino acid in cyanobacteria, but its transport properties remain largely unknown. In this study, we found that a halotolerant cyanobacterium, Aphanothece halophytica, contained a sodium dependent glutamate transporter (ApGltS). The deduced amino acid sequence of ApGltS exhibited low homology (18-19% identity) to GltS from Synechocystis sp. PCC 6803 (slr1145) and Escherichia coli. The predicted ApGltS consisted of 476 amino acid residues with a molecular weight of 50,976 Da. As analysed by hydropathy profiling, ApGltS contains 11 transmembrane segments. The ApgltS gene was isolated and expressed in E. coli ME9107, which is deficient in glutamate uptake. ME9107, expressing ApGltS, took up glutamate and its rates increased with increasing concentrations of NaCl. Kinetics studies revealed that ApGltS is a high-affinity glutamate transporter with a K(m) of about 5 µM. The presence of 0.5 M NaCl in the assay medium increased V(max) by about 3-fold. Competition experiments revealed that glutamate, glutamine, aspartate, and asparagine inhibited glutamate uptake. The level of mRNA for ApgltS was higher in A. halophytica grown at high salinity. Under high salinity conditions supplemented with glutamate, A. halophytica showed a significant increase in intracellular glycine betaine.
authors.affiliation: Graduate School of Environmental and Human Sciences, Meijo University, Nagoya 468-8502, Japan.
authors.forename: Bongkoj
authors.initials: B
authors.lastname: Boonburapong
authors.forename: Surasak
authors.initials: S
authors.lastname: Laloknam
authors.forename: Nana
authors.initials: N
authors.lastname: Yamada
authors.forename: Aran
authors.initials: A
authors.lastname: Incharoensakdi
authors.forename: Teruhiro
authors.initials: T
authors.lastname: Takabe
mesh_terms: D000595:Amino Acid Sequence; D027322:Amino Acid Transport System X-AG / Q000235:genetics / Q000378:metabolism*; D026922:Amino Acid Transport Systems, Acidic / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001622:Betaine / Q000378:metabolism; D000458:Cyanobacteria / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D054712:Salinity; D055049:Salt Tolerance / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride / Q000494:pharmacology*; D013379:Substrate Specificity; D027981:Symporters / Q000235:genetics / Q000378:metabolism
chemical_list: D027322:Amino Acid Transport System X-AG; D026922:Amino Acid Transport Systems, Acidic; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D027981:Symporters; C066603:gltS protein, E coli; D018698:Glutamic Acid; D001622:Betaine; D012965:Sodium Chloride