Research Projects

Microbial natural products (MNPs) including antibiotics have been extensively harnessed due to their remarkable biological activities and they remain indispensable across various sectors, including healthcare, pharmaceuticals and agriculture. Streptomyces are the Gram-positive soil dwelling filamentous bacteria of genus Actinobacteria, produce numerous MNPs contributing as a source for over 80% of the antibiotics. These MNPs are the products of biosynthetic gene clusters (BGCs), encoding enzymes catalyzing MNP synthesis. The expression of these BGCs are under tight control of transcription regulators (TRs) responding to diffusible signaling molecules (SMs) of the cellular/environmental origins. One of the abundant and first discovered classes of diffusible SMs in Actinobacteria are the γ-butyrolactones (GBLs). It is shown that these GBLs operate at nanomolar concentrations to mount response in their cognate TR controlling MNP biosynthesis. However, the molecular basis of control over biosynthesis is poorly understood as there are no available structures of TRs in complex with GBLs in the public domain. To understand the molecular basis of TR control, we aim to investigate the transcription regulation by BarA and FarA of S. virginiae and S. lavendulae FRI-5, respectively, from TetR family of TRs. TetR is an archetypal example of the family having both DNA binding domain (DBD) and SM binding domain (SMBD) on a single polypeptide chain. SM binding induces allostery in TetR DBD resulting in derepression from the promoter. Based on the amino acids sequence similarity in the family, it was shown that the DBD is highly conserved, however, the SMBD is diverse, allowing the TetR family of TRs to respond to a spectrum of SMs. TRs under investigation, BarA controls virginiamycin responding to virginiae butanolides (VBs) whereas, FarA regulates showdomycin and minimycin in S. lavendulae responding to IM-2, a GBL. While the results from gene deletion studies revealed the regulatory role of BarA and FarA, however, the molecular basis of GBLs induced allostery resulting the onset of antibiotic biosynthesis remains unclear. Insights from BarA and FarA responding to VBs and IM-2, respectively, enables to uncover the mechanism of transcription regulation over biosynthesis and aids exploiting BGC potential for enhanced MNP production. Moreover, findings from this study is anticipated to aid silent BGC activation under laboratory conditions by promoter engineering for novel MNP discovery. This knowledge will be handy to tap the silent BGCs which are the tremendous source for novel antibiotics and other MNPs.