title: Structural mechanism of transcriptional autorepression of the Escherichia coli RelB/RelE antitoxin/toxin module.
abstract: The Escherichia coli chromosomal relBE operon encodes a toxin-antitoxin system, which is autoregulated by its protein products, RelB and RelE. RelB acts as a transcriptional repressor and RelE functions as a cofactor to enhance the repressor activity of RelB. Here, we present the NMR-derived structure of a RelB dimer and show that a RelB dimer recognizes a hexad repeat in the palindromic operator region through a ribbon-helix-helix motif. Our biochemical data show that two weakly associated RelB dimers bind to the adjacent repeats in the 3'-site of the operator (O(R)) at a moderate affinity (K(d), approximately 10(-5) M). However, in the presence of RelE, a RelB tetramer binds two distinct binding sites within the operator region, each with an enhanced affinity (K(d), approximately 10(-6) M for the low-affinity site, O(L), and 10(-8) M for the high-affinity site, O(R)). We propose that the enhanced affinity for the operator element is mediated by a cooperative DNA binding by a pair of RelB dimers and that the interaction between RelB dimers is strongly augmented by the presence of the cognate toxin RelE.
authors.affiliation: Division of Signaling Biology, Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Guang-Yao
authors.initials: GY
authors.lastname: Li
authors.forename: Yonglong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Masayori
authors.initials: M
authors.lastname: Inouye
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Ikura
mesh_terms: D000992:Antitoxins / Q000737:chemistry*; D001427:Bacterial Toxins / Q000737:chemistry*; D001483:Base Sequence; D002942:Circular Dichroism; D004269:DNA, Bacterial / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009875:Operator Regions, Genetic / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry*; D014158:Transcription, Genetic; D051841:Transcription Factor RelB
chemical_list: D000992:Antitoxins; D001427:Bacterial Toxins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; C465567:RelB protein, E coli; D051841:Transcription Factor RelB; C465566:RelE protein, E coli