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

CABRUJA MATÍAS; LARRIEUX N; GRAMAJO H; SALA C; DIACOVICH L; BUSCHIAZZO A; MONDINO S; LARA J; COLE S; GAGO GABRIELA

Lucca

Conferencia; Gordon Research Conference: Tuberculosis Drug Discovery & Development; 2017

Gordon Research Conference

Besides the relevance of lipid derived molecules in M. tuberculosis 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 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 M. tuberculosis, 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, 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 acid in the growth medium. Global lipidomic analysis indicates that under fatty acid biosynthesis inhibition there is a strong remodeling of the cell wall components. Our studies provide a wealth of information that will let us evaluate how M. tuberculosis responds to the alteration, or absence of the novo FA and MA acid biosynthesis, and how important is to maintain lipid homeostasis in the context of the macrophages environment and in the progression of the infection. Furthermore, biochemical and genetics experiments 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 the C20-CoA (a product of FAS-I) with FasR by structural studies. Thus, the crystal structure of 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.