title: Lactococcus lactis ZitR is a zinc-responsive repressor active in the presence of low, nontoxic zinc concentrations in vivo.
abstract: In the family Streptococcaceae, the genes encoding zinc ABC uptake systems (called zit or adc) are regulated by a coencoded MarR family member (i.e., ZitR or AdcR), whereas in the great majority of bacteria, these genes are regulated by Zur, the Fur-like zinc-responsive repressor. We studied the zit operon from Lactococcus lactis and its regulation in response to Zn(II) in vivo. zit transcription is repressed by Zn(II) in a wide concentration range starting from nontoxic micromolar levels and is derepressed at nanomolar concentrations. The level of zit promoter downregulation by environmental Zn(II) is correlated with the intracellular zinc content. The helix-turn-helix domain of ZitR is required for downregulation. In vitro, the purified protein is a dimer that complexes up to two zinc ligands per monomer and specifically binds two intact palindromic operator sites overlapping the -35 and -10 boxes of the zit promoter. DNA binding is abolished by the chelator EDTA or TPEN and fully restored by Zn(II) addition, indicating that the active repressor complexes Zn(II) with high affinity. These results suggest that derepression under starvation conditions could be an essential emergency mechanism for preserving Zn(II) homeostasis by uptake; under Zn(II)-replete conditions, the function of ZitR repression could be to help save energy rather than to avoid Zn(II) toxicity. The characterization of a MarR family zinc-responsive repressor in this report gives insight into the way Streptococcaceae efficiently adapt to Zn(II) fluctuations in their diverse ecological niches.
authors.affiliation: INRA, UMR1319 Micalis (Microbiologie de l'Alimentation au Service de la Santé), Bât 222, Domaine de Vilvert, F-78352 Jouy-en-Josas Cedex, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Llull
authors.forename: Olivier
authors.initials: O
authors.lastname: Son
authors.forename: Sandrine
authors.initials: S
authors.lastname: Blanié
authors.forename: Julien
authors.initials: J
authors.lastname: Briffotaux
authors.forename: Eric
authors.initials: E
authors.lastname: Morello
authors.forename: Hélène
authors.initials: H
authors.lastname: Rogniaux
authors.forename: Olivier
authors.initials: O
authors.lastname: Danot
authors.forename: Isabelle
authors.initials: I
authors.lastname: Poquet
mesh_terms: D000595:Amino Acid Sequence; D004269:DNA, Bacterial / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D018257:Helix-Loop-Helix Motifs; D013294:Lactococcus lactis / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009876:Operon; D011401:Promoter Regions, Genetic; D025941:Protein Interaction Mapping; D055503:Protein Multimerization; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D016415:Sequence Alignment; D015032:Zinc / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D012097:Repressor Proteins; D015032:Zinc