Investigating interactions between methylenomycin furan microbial hormones and transcriptional repressors in Streptomyces coelicolor.

An interesting insight has been developed into the roles of a paralogous pair of transcriptional regulators MmfR and MmyR in the regulation of methylenomycin antibiotic biosynthesis in Streptomyces coelicolor. Research involved the development and use of a luciferase reporter assay, optimised for use in GC high bacteria. MmfR belongs to the TetR-family of transcriptional repressor proteins and works as a single component system, binding to DNA at one of three methylenomycin auto-regulatory response element (MARE) operators. Here it represses transcription of five different operons until a conformational change is brought about by specific binding to one of five small signalling molecules; the methylenomycin furans (MMFs). This investigation revealed that the five different MmfR-regulated operons have promoters of differing strengths, which is also contributed to by a variation in the strength of MmfR binding to the three MARE operator sites. Each of the five naturally produced MMF ligands were also shown to have a different efficacy for deactivating and displacing MmfR. An in silico analysis of the MmfR primary and tertiary structures, followed by in vivo mutagenesis, revealed the presence of two tyrosine residues implicated in ligand binding. The paralogue MmyR was shown to vary in activity from that of MmfR. It showed weaker, but significant binding to only two out of the three MARE operator sites, binding with different affinities to each, and no significant removal of repression was seen in the presence of the MMF ligands. The MmfR/MMF/MARE operator system shows promise as something that can be developed into a novel inducible expression system for use in GC high bacteria. However, whether this system can be adapted to be efficient in multiple hosts is yet to be seen, with affinity for the MARE operators from exogenous regulatory proteins predicted