title: Conserved ABC Transport System Regulated by the General Stress Response Pathways of Alpha- and Gammaproteobacteria.
abstract: Brucella abortusσE1is an EcfG family sigma factor that regulates the transcription of dozens of genes in response to diverse stress conditions and is required for maintenance of chronic infection in a mouse model. A putative ATP-binding cassette transporter operon,bab1_0223-bab1_0226, is among the most highly activated gene sets in the σE1regulon. The proteins encoded by the operon resemble quaternary ammonium-compatible solute importers but are most similar in sequence to the broadly conserved YehZYXW system, which remains largely uncharacterized. Transcription ofyehZYXWis activated by the general stress sigma factor σSinEnterobacteriaceae, which suggests a functional role for this transport system in bacterial stress response across the classesAlphaproteobacteriaandGammaproteobacteriaWe present evidence thatB. abortusYehZYXW does not function as an importer of known compatible solutes under physiological conditions and does not contribute to the virulence defect of a σE1-null strain. The solein vitrophenotype associated with genetic disruption of this putative transport system is reduced growth in the presence of high Li+ion concentrations. A crystal structure ofB. abortusYehZ revealed a class II periplasmic binding protein fold with significant structural homology toArchaeoglobus fulgidusProX, which binds glycine betaine. However, the structure of the YehZ ligand-binding pocket is incompatible with high-affinity binding to glycine betaine. This is consistent with weak measured binding of YehZ to glycine betaine and related compatible solutes. We conclude that YehZYXW is a conserved, stress-regulated transport system that is phylogenetically and functionally distinct from quaternary ammonium-compatible solute importers.IMPORTANCEBrucella abortusσE1regulates transcription in response to stressors encountered in its mammalian host and is necessary for maintenance of chronic infection in a mouse model. The functions of the majority of genes regulated by σE1remain undefined. We present a functional/structural analysis of a conserved putative membrane transport system (YehZYXW) whose expression is strongly activated by σE1Though annotated as a quaternary ammonium osmolyte uptake system, experimental physiological studies and measured ligand-binding properties of the periplasmic binding protein (PBP), YehZ, are inconsistent with this function. A crystal structure ofB. abortusYehZ provides molecular insight into differences between bona fide quaternary ammonium osmolyte importers and YehZ-related proteins, which form a distinct phylogenetic and functional group of PBPs.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA.|Howard Taylor Ricketts Laboratory, University of Chicago, Chicago, Illinois, USA.
authors.forename: Julien
authors.initials: J
authors.lastname: Herrou
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA.|Howard Taylor Ricketts Laboratory, University of Chicago, Chicago, Illinois, USA.
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Willett
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA.|Howard Taylor Ricketts Laboratory, University of Chicago, Chicago, Illinois, USA.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Czyż
authors.affiliation: Argonne National Laboratory, Argonne, Illinois, USA.
authors.forename: Gyorgy
authors.initials: G
authors.lastname: Babnigg
authors.affiliation: Argonne National Laboratory, Argonne, Illinois, USA.
authors.forename: Youngchang
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA scrosson@uchicago.edu.|Howard Taylor Ricketts Laboratory, University of Chicago, Chicago, Illinois, USA.|Department of Microbiology, University of Chicago, Chicago, Illinois, USA.
authors.forename: Sean
authors.initials: S
authors.lastname: Crosson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001622:Betaine; D001692:Biological Transport; D002003:Brucella abortus / Q000502:physiology*; D002460:Cell Line; D005260:Female; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D009876:Operon / Q000502:physiology; D010802:Phylogeny; D013312:Stress, Physiological / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D001622:Betaine
keywords: ABC transporter; Alphaproteobacteria; EcfG; RpoS; YehZ; YehZYXW; general stress response; lithium; sigma factor