title: Identification of a third osmoprotectant transport system, the osmU system, in Salmonella enterica.
abstract: The growth of Salmonella enterica serovar Typhimurium mutants lacking the ProP and ProU osmoprotectant transport systems is stimulated by glycine betaine in high-osmolarity media, suggesting that this organism has an additional osmoprotectant transport system. Bioinformatic analysis revealed that the genome of this organism contains a hitherto-unidentified operon, designated osmU, consisting of four genes whose products show high similarity to ABC-type transport systems for osmoprotectants in other bacteria. The osmU operon was inactivated by a site-directed deletion, which abolished the ability of glycine betaine to alleviate the inhibitory effect of high osmolarity and eliminated the accumulation of [(14)C]glycine betaine and [(14)C]choline-O-sulfate in high-osmolarity media in a strain lacking the ProP and ProU systems. Although the OsmU system can take up glycine betaine and choline-O-sulfate, these two osmoprotectants are recognized at low affinity by this transporter, suggesting that there might be more efficient substrates that are yet to be discovered. The transcription of osmU is induced 23-fold by osmotic stress (0.3 M NaCl). The osmU operon is present in the genomes of a number of Enterobacteriaceae, and orthologs of the OsmU system can be recognized in a wide variety of Bacteria and Archaea. The structure of the periplasmic binding protein component of this transporter, OsmX, was modeled on the crystallographic structure of the glycine betaine-binding protein ProX of Archaeoglobus fulgidus; the resultant model indicated that the amino acids that constitute substrate-binding site, including an "aromatic cage" made up of four tyrosines, are conserved between these two proteins.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana, USA.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Frossard
authors.forename: Aftab A
authors.initials: AA
authors.lastname: Khan
authors.forename: Eric C
authors.initials: EC
authors.lastname: Warrick
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Gately
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Hanson
authors.forename: Michael L
authors.initials: ML
authors.lastname: Oldham
authors.forename: David Avram
authors.initials: DA
authors.lastname: Sanders
authors.forename: Laszlo N
authors.initials: LN
authors.lastname: Csonka
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism*; D001622:Betaine / Q000378:metabolism; D019295:Computational Biology; D003470:Culture Media / Q000737:chemistry; D017353:Gene Deletion; D020869:Gene Expression Profiling; D005798:Genes, Bacterial; D008958:Models, Molecular; D009876:Operon; D009997:Osmotic Pressure; D011487:Protein Conformation; D012486:Salmonella typhimurium / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D018528:ATP-Binding Cassette Transporters; D003470:Culture Media; D001622:Betaine