title: Studies of IscR reveal a unique mechanism for metal-dependent regulation of DNA binding specificity.
abstract: IscR from Escherichia coli is an unusual metalloregulator in that both apo and iron sulfur (Fe-S)-IscR regulate transcription and exhibit different DNA binding specificities. Here, we report structural and biochemical studies of IscR suggesting that remodeling of the protein-DNA interface upon Fe-S ligation broadens the DNA binding specificity of IscR from binding the type 2 motif only to both type 1 and type 2 motifs. Analysis of an apo-IscR variant with relaxed target-site discrimination identified a key residue in wild-type apo-IscR that, we propose, makes unfavorable interactions with a type 1 motif. Upon Fe-S binding, these interactions are apparently removed, thereby allowing holo-IscR to bind both type 1 and type 2 motifs. These data suggest a unique mechanism of ligand-mediated DNA site recognition, whereby metallocluster ligation relocates a protein-specificity determinant to expand DNA target-site selection, allowing a broader transcriptomic response by holo-IscR.
authors: Genomic Medicine Program, The Methodist Hospital Research Institute, Houston, Texas, USA.
authors: Senapathy
authors: S
authors: Rajagopalan
authors: Sarah J
authors: SJ
authors: Teter
authors: Petrus H
authors: PH
authors: Zwart
authors: Richard G
authors: RG
authors: Brennan
authors: Kevin J
authors: KJ
authors: Phillips
authors: Patricia J
authors: PJ
authors: Kiley
mesh_terms: D018360:Crystallography, X-Ray; D004269:DNA, Bacterial / Q000378:metabolism*; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D008670:Metals / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D013379:Substrate Specificity; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C499695:IscR protein, E coli; D008670:Metals; D014157:Transcription Factors
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