Investigation of quorum sensing molecules in the regulation of antibiotic production in Streptomyces coelicolor

Antimicrobial resistance and the biosynthesis of secondary metabolites including the life-saving antibiotics in Streptomycetes are tightly controlled by the tetracycline repressor family of transcription regulators (TetR-FTRs). These regulators achieve such phenomenal governance by binding to their respective target DNA sequence using the conserved N-terminal DNA binding domain (DBD). The TetR-FTRs also have diverse C-terminal regulatory domains which communicate with the DBDs via connector helices. Upon binding of a specific signaling molecule, the TetR-FTRs undergo allosteric transition resulting in abrogated DNA binding thereby ultimately triggering activation of the downstream pathways under their control.
In this thesis, the structural and functional aspects of a TetR-FTR, CprB from Streptomyces coelicolor is investigated. CprB belongs to a class of TetR-FTRs induced by γ-butyrolactones (GBLs) and the first crystal structure of protein-DNA complex for this class is reported here. From the structure, it was observed that as a consequence of DNA binding, CprB undergoes restructuring in its dimeric interface inducing a pendulum-like shift in the DBD. Additionally, the outcomes from the studies aimed to identify the target DNA sequences for CprB, which suggested that it plays a pleiotropic role and also serves as an autoregulator. Another important objective of this thesis was to identify the signaling molecule(s) for CprB. The results show that CprB recognises multiple GBLs and which is in accordance with the hypothesis that Streptomycetes possesses both intra- and inter-species signal detection systems to overcome the recurrent and often extreme variations of their micro-environmental conditions.