Structural basis for control of antibiotic production by bacterial hormones

Actinobacteria produce numerous antibiotics and other specialised metabolites with important applications in medicine and agriculture. Diffusible hormones frequently control the production of such metabolites by binding TetR family transcriptional repressors (TFTRs), but the molecular basis for this remains unclear. The production of methylenomycin antibiotics in Streptomyces coelicolor A3(2) is initiated by binding of 2-alkyl-4-hydroxymethylfuran-3-carboxylic acid (AHFCA) hormones to the TFTR MmfR. Here, we report the X-ray crystal structure of an MmfR-AHFCA complex, establishing the structural basis for hormone recognition. We also elucidate the mechanism for DNA release upon hormone binding by single particle cryo-electron microscopy of an MmfR-operator complex. Electrophoretic mobility shift assays with MmfR mutants and synthetic AHFCA analogues illuminate the role played by individual amino acid residues and hormone functional groups in ligand recognition and DNA release. These findings will facilitate the exploitation of Actinobacterial hormones and their associated TFTRs in synthetic biology and novel antibiotic discovery.