CONICET | Buscador de Institutos y Recursos Humanos

The complex lipids present in the cell envelope of Mycobacterium tuberculosis (Mtb) constitute a unique structure critical to the virulence of this pathogen. The environmental signals and regulatory network involved in the global regulation of lipid metabolism in this bacterium is largely unknown; although examples of transcriptional and post-translational mechanism of regulation have recently been described. One of the key transcriptional regulators is FasR, a protein that binds to the fas-acpS promoter region and controls the de novo fatty acid biosynthesis becoming a central component involved in maintaining lipid homeostasis in mycobacteria. In this work, we present the X-ray structure of Mtb FasR and in complex with a C20-acyl-CoA, which corresponds to the pool of long-chain acyl-CoAs, the effector molecules that coordinate the expression of the two fatty acid synthase (FAS) systems present in mycobacteria. The effector molecule was found seated within a hydrophobic tunnel open at both ends and that extends all along the core of the ellipsoidal C-terminal effector-binding domain of FasR. Electrophoretic mobility shift assays with FasR mutants generated to prevent the binding of the FasR-ligand or to uncouple the transmission of the signal from the effector to the HTH domain of the regulator, gave further insights into the structural bases involved in the FasR-ligand recognition and FasR-DNA interaction. The structural characterization of this novel transcriptional regulator provides new insights into the regulatory mechanisms that maintain lipid homeostasis in Mtb and open the opportunity to identify molecules that could work as antimycobacterial compounds by inhibiting the activity of the transcriptional regulator.