title: The Treponema pallidum tro operon encodes a multiple metal transporter, a zinc-dependent transcriptional repressor, and a semi-autonomously expressed phosphoglycerate mutase.
abstract: The Treponema pallidum tro operon encodes an ABC transporter (TroABCD), a transcriptional repressor (TroR), and the essential glycolytic enzyme phosphoglycerate mutase (Gpm). The apparently discordant observations that the solute binding protein (TroA) binds Zn2+, whereas DNA binding by TroR in vitro is Mn2+-dependent, have generated uncertainty regarding the identities of the ligand(s) and co-repressor(s) of the permease. Moreover, this operonic structure suggests that Gpm expression, and hence glycolysis, the sole source of ATP for the bacterium, would be suspended during TroR-mediated repression. To resolve these discrepancies, we devised an experimental strategy permitting a more direct assessment of Tro operon function and regulation. We report that (i) apo-TroA has identical affinities for Zn2+ and Mn2+; (ii) the Tro transporter expressed in Escherichia coli imports Zn2+, Mn2+, and possibly iron; (iii) TroR represses transporter expression in E. coli at significantly lower concentrations of Zn2+ than of Mn2+; and (iv) TroR-mediated repression causes a disproportionately greater down-regulation of the transporter genes than of gpm. The much higher concentrations of Zn2+ than of Mn2+ in human body fluids suggests that Zn2+ is both the primary substrate and co-repressor of the permease in vivo. Our data also indicate that Gpm expression and, therefore, glycolysis would not be abrogated when T. pallidum encounters high Zn2+ levels.
authors.affiliation: Center for Microbial Pathogenesis, University of Connecticut Health Center, Farmington, Connecticut 06030-3710, USA. KHazlett@up.uchc.edu
authors.forename: Karsten R O
authors.initials: KR
authors.lastname: Hazlett
authors.forename: Frank
authors.initials: F
authors.lastname: Rusnak
authors.forename: David G
authors.initials: DG
authors.lastname: Kehres
authors.forename: Scott W
authors.initials: SW
authors.lastname: Bearden
authors.forename: Carson J
authors.initials: CJ
authors.lastname: La Vake
authors.forename: Morgan E
authors.initials: ME
authors.lastname: La Vake
authors.forename: Michael E
authors.initials: ME
authors.lastname: Maguire
authors.forename: Robert D
authors.initials: RD
authors.lastname: Perry
authors.forename: Justin D
authors.initials: JD
authors.lastname: Radolf
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins; D004305:Dose-Response Relationship, Drug; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology; D009876:Operon / Q000187:drug effects / Q000502:physiology; D033902:Periplasmic Binding Proteins / Q000235:genetics* / Q000378:metabolism; D010736:Phosphoglycerate Mutase / Q000235:genetics* / Q000378:metabolism; D011817:Rabbits; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D013587:Syphilis / Q000382:microbiology; D014158:Transcription, Genetic / Q000502:physiology; D014210:Treponema pallidum / Q000201:enzymology / Q000235:genetics*; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D033902:Periplasmic Binding Proteins; D012097:Repressor Proteins; C120377:TroA protein, Treponema pallidum; C121664:TroR protein, Treponema pallidum; D008345:Manganese; D010736:Phosphoglycerate Mutase; D015032:Zinc