Monovalent Cation Dependent Oligomerization and DNA Binding of MoyR: a GntR family monooxygenase regulator in Mycobacterium tuberculosis

Abstract

Bacteria constitute a large domain of prokaryotic microorganisms with a remarkable ability to perceive environmental stimuli, and respond efficiently to environmental stresses by regulation of gene expression mediated by transcriptional regulators. M. tuberculosis is a classic example of this, where ample studies have provided evidence of how the transcriptional regulators are involved in various survival mechanisms in the bacterium. Mycobacterium tuberculosis is a well-known pathogen due to the emergence of drug resistance associated with it, and the genome of M. tuberculosis encodes many transcriptional regulators. Our work explicates the mechanism of K+/ Na+ mediated oligomerization and DNA binding of MoyR. In vitro assays revealed a complex pattern of MoyR oligomerization depending on monovalent cation concentrations where MoyR tends to form tetramers and hexamers which directly affect the MoyR affinity to its cognate DNA. The tetramer bound DNA was found to be highly stable even at high monovalent cation concentrations such as 500 mM which is unusual for a protein-DNA binding in a mesophilic bacteria. GntR proteins are substantially known to bind the DNA as homodimers in a two-fold symmetry, but this study is the second, that reports of a tetrameric GntR protein assembly after the GntR regulator Atu1419 in Agrobacterium fabrum. MoyR binds with high affinity (Kd,app = 3.47 nM) and specificity to the shared promoter region between divergently oriented Rv0789c-Rv0790c-Rv0791c-moyR operon and Rv0793. The moyR gene cluster was identified as a conserved region and most of the adjacent genes are homologous to monooxygenases which highly likely to be likely to be inplicated in a polyketide antibiotic synthesis pathway of the bacterium and this can provide a novel paradigm to the antibiotic tolerance and resistance of M. tuberculosis wherein this elicits the importance of MoyR as a drug target.