1. The induction mechanism of the flavonoid-responsive regulator FrrA.
- Author
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Werner N, Werten S, Hoppen J, Palm GJ, Göttfert M, and Hinrichs W
- Subjects
- Binding Sites genetics, Bradyrhizobium genetics, Bradyrhizobium pathogenicity, Crystallography, X-Ray, DNA-Binding Proteins ultrastructure, Flavonoids biosynthesis, Gene Expression Regulation, Bacterial genetics, Ligands, Protein Binding genetics, Protein Conformation, Ribosomal Proteins ultrastructure, Glycine max microbiology, DNA-Binding Proteins genetics, Flavonoids genetics, Ribosomal Proteins genetics, Glycine max genetics
- Abstract
Bradyrhizobium diazoefficiens, a bacterial symbiont of soybean and other leguminous plants, enters a nodulation-promoting genetic programme in the presence of host-produced flavonoids and related signalling compounds. Here, we describe the crystal structure of an isoflavonoid-responsive regulator (FrrA) from Bradyrhizobium, as well as cocrystal structures with inducing and noninducing ligands (genistein and naringenin, respectively). The structures reveal a TetR-like fold whose DNA-binding domain is capable of adopting a range of orientations. A single molecule of either genistein or naringenin is asymmetrically bound in a central cavity of the FrrA homodimer, mainly via C-H contacts to the π-system of the ligands. Strikingly, however, the interaction does not provoke any conformational changes in the repressor. Both the flexible positioning of the DNA-binding domain and the absence of structural change upon ligand binding are corroborated by small-angle X-ray scattering (SAXS) experiments in solution. Together with a model of the promoter-bound state of FrrA our results suggest that inducers act as a wedge, preventing the DNA-binding domains from moving close enough together to interact with successive positions of the major groove of the palindromic operator., (© 2021 The Authors. The FEBS Journal published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)
- Published
- 2022
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