Transcriptional regulation of fatty acid metabolism in Mycobacterium tuberculosis: identification and validation of new drug targets

CABRUJA, MATÍAS; GRAMAJO, HUGO AND GAGO, GABRIELA.

Congreso; Gordon Conference; 2017

Besides the relevance of lipid derived molecules in Mtb pathogenicity, little is known about the environmental signals and regulatory cascades involved in the global regulation of lipid metabolism in this bacterium, and how lipid homeostasis is maintained for Mtb survival and during infection. Our work is directed to fulfill some of these gaps by studying in detail the elements and mechanisms that regulate lipid homeostasis in Mtb, how they impact in the biosynthesis and composition of its cell wall and how the host-pathogen lipid metabolisms interact. Mycobacteria are unusual in possessing two fatty acid synthase (FAS) systems, the so called eukaryotic-like type I and the prokaryotic-like type II. To demonstrate that FAS I and FAS II systems are strictly co-regulated in order to maintain lipid homeostasis in Mtb, we initiated our research project with the identification and characterization of the components of the transcriptional network that keeps the two FAS systems tightly regulated. For this, we identified and characterized a specific regulator that binds above Pfas and named it FasR. FasR is a positive regulator of the fas-acpS operon genes and is essential in M. smegmatis. We have now constructed a conditional fasR mutant in M. tuberculosis and found that this strain has severe growth defects in the absence of fatty acis in the growth medium. A combined transcriptomic, proteomic and lipidomic analysis was performed on the mutant strain. Altogether, the results indicate that under fatty acid biosynthesis inhibition there is a strong remodeling of the cell wall components. Moreover, preliminary results indicate that the fasR mutant strain is attenuated in mouse infection experiments. Our studies provide a wealth of information that will let us evaluate how Mtb responds to the alteration, or absence, of the de novo FA and MA acid biosynthesis, and how important is to maintain lipid homeostasis in the context of the macrophage environment and in the progression of the infection. Furthermore, biochemical and genetics experiments had suggested that long-chain acyl-CoAs are the effector molecules that modulate the affinity of FasR for its DNA binding sequences and therefore the expression of the essential fas-acpS operon. We have now confirmed the interaction of a C20-CoA (a product of FAS I) with FasR by structural studies. Thus, the crystal structure of this FasR and FasR-C20-CoA could help us search and identify structure-based inhibitors that could then be tested as a new category of antimycobacterial compounds