title: Evolution of metal(loid) binding sites in transcriptional regulators.
abstract: Expression of the genes for resistance to heavy metals and metalloids is transcriptionally regulated by the toxic ions themselves. Members of the ArsR/SmtB family of small metalloregulatory proteins respond to transition metals, heavy metals, and metalloids, including As(III), Sb(III), Cd(II), Pb(II), Zn(II), Co(II), and Ni(II). These homodimeric repressors bind to DNA in the absence of inducing metal(loid) ion and dissociate from the DNA when inducer is bound. The regulatory sites are often three- or four-coordinate metal binding sites composed of cysteine thiolates. Surprisingly, in two different As(III)-responsive regulators, the metalloid binding sites were in different locations in the repressor, and the Cd(II) binding sites were in two different locations in two Cd(II)-responsive regulators. We hypothesize that ArsR/SmtB repressors have a common backbone structure, that of a winged helix DNA-binding protein, but have considerable plasticity in the location of inducer binding sites. Here we show that an As(III)-responsive member of the family, CgArsR1 from Corynebacterium glutamicum, binds As(III) to a cysteine triad composed of Cys(15), Cys(16), and Cys(55). This binding site is clearly unrelated to the binding sites of other characterized ArsR/SmtB family members. This is consistent with our hypothesis that metal(loid) binding sites in DNA binding proteins evolve convergently in response to persistent environmental pressures.
authors.affiliation: Departamento de Biología Molecular,Área de Microbiología, Facultad de Biología-Ambientales, Universidad de León, 24071 León, Spain and the.
authors.forename: Efrén
authors.initials: E
authors.lastname: Ordóñez
authors.affiliation: Department of Biochemistry and Molecular Biology, Wayne State University, School of Medicine, Detroit, Michigan 48201.
authors.forename: Saravanamuthu
authors.initials: S
authors.lastname: Thiyagarajan
authors.affiliation: Department of Biochemistry and Molecular Biology, Wayne State University, School of Medicine, Detroit, Michigan 48201.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Cook
authors.affiliation: Department of Biochemistry and Molecular Biology, Wayne State University, School of Medicine, Detroit, Michigan 48201.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Stemmler
authors.affiliation: Departamento de Biología Molecular,Área de Microbiología, Facultad de Biología-Ambientales, Universidad de León, 24071 León, Spain and the.
authors.forename: José A
authors.initials: JA
authors.lastname: Gil
authors.affiliation: Departamento de Biología Molecular,Área de Microbiología, Facultad de Biología-Ambientales, Universidad de León, 24071 León, Spain and the.
authors.forename: Luís M
authors.initials: LM
authors.lastname: Mateos
authors.affiliation: Department of Biochemistry and Molecular Biology, Wayne State University, School of Medicine, Detroit, Michigan 48201. Electronic address: brosen@med.wayne.edu.
authors.forename: Barry P
authors.initials: BP
authors.lastname: Rosen
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology*; D001483:Base Sequence; D001665:Binding Sites; D048230:Corynebacterium glutamicum / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D008670:Metals / Q000737:chemistry; D008954:Models, Biological; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000737:chemistry* / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D008670:Metals; D015534:Trans-Activators; D004247:DNA