title: Direct substitution and assisted dissociation pathways for turning off transcription by a MerR-family metalloregulator.
abstract: Metalloregulators regulate transcription in response to metal ions. Many studies have provided insights into how transcription is activated upon metal binding by MerR-family metalloregulators. In contrast, how transcription is turned off after activation is unclear. Turning off transcription promptly is important, however, as the cells would not want to continue expressing metal resistance genes and thus waste energy after metal stress is relieved. Using single-molecule FRET measurements we studied the dynamic interactions of the copper efflux regulator (CueR), a Cu(+)-responsive MerR-family metalloregulator, with DNA. Besides quantifying its DNA binding and unbinding kinetics, we discovered that CueR spontaneously flips its binding orientation at the recognition site. CueR also has two different binding modes, corresponding to interactions with specific and nonspecific DNA sequences, which would facilitate recognition localization. Most strikingly, a CueR molecule coming from solution can directly substitute for a DNA-bound CueR or assist the dissociation of the incumbent CueR, both of which are unique examples for any DNA-binding protein. The kinetics of the direct protein substitution and assisted dissociation reactions indicate that these two unique processes can provide efficient pathways to replace a DNA-bound holo-CueR with apo-CueR, thus turning off transcription promptly and facilely.
authors.affiliation: Departments of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Chandra P
authors.initials: CP
authors.lastname: Joshi
authors.forename: Debashis
authors.initials: D
authors.lastname: Panda
authors.forename: Danya J
authors.initials: DJ
authors.lastname: Martell
authors.forename: Nesha May
authors.initials: NM
authors.lastname: Andoy
authors.forename: Tai-Yen
authors.initials: TY
authors.lastname: Chen
authors.forename: Ahmed
authors.initials: A
authors.lastname: Gaballa
authors.forename: John D
authors.initials: JD
authors.lastname: Helmann
authors.forename: Peng
authors.initials: P
authors.lastname: Chen
mesh_terms: D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins / Q000378:metabolism*; D004247:DNA / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D007477:Ions / Q000737:chemistry*; D007700:Kinetics; D008670:Metals / Q000737:chemistry; D008954:Models, Biological; D011485:Protein Binding; D013438:Sulfhydryl Compounds / Q000737:chemistry; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D007477:Ions; C051124:MerR protein, Bacteria; D008670:Metals; D013438:Sulfhydryl Compounds; D004247:DNA