Tetracycline Repressor Allostery Does not Depend on Divalent Metal Recognition.Werten, S., Dalm, D., Palm, G.J., Grimm, C.C., Hinrichs, W.
(2014) Biochemistry 53: 7990
- PubMed: 25432019
- DOI: https://doi.org/10.1021/bi5012805
- Primary Citation of Related Structures:
2XPU, 4D7M, 4D7N, 4V2F, 4V2G
- PubMed Abstract:
Genes that render bacteria resistant to tetracycline-derived antibiotics are tightly regulated by repressors of the TetR family. In their physiologically relevant, magnesium-complexed form, tetracyclines induce allosteric rearrangements in the TetR homodimer, leading to its release from the promoter and derepression of transcription. According to earlier crystallographic work, recognition of the tetracycline-associated magnesium ion by TetR is crucial and triggers the allosteric cascade. Nevertheless, the derivative 5a,6-anhydrotetracycline, which shows an increased affinity for TetR, causes promoter release even in the absence of magnesium. To resolve this paradox, it has been proposed that metal-free 5a,6-anhydrotetracycline acts via an exceptional, conformationally different induction mode that circumvents the normal magnesium requirement. We have tested this hypothesis by determining crystal structures of TetR-5a,6-anhydrotetracycline complexes in the presence of magnesium, ethylenediaminetetraacetic acid, or high concentrations of potassium. Analysis of these three structures reveals that, irrespective of the metal, the effects of 5a,6-anhydrotetracycline binding are indistinguishable from those of canonical induction by other tetracyclines. Together with a close scrutiny of the earlier evidence of a metal-triggered mechanism, these results demonstrate that magnesium recognition per se is not a prerequisite for tetracycline repressor allostery.
Department of Molecular Structural Biology, Institute for Biochemistry, University of Greifswald , Felix-Hausdorff-Strasse 4, D-17487 Greifswald, Germany.