CHARACTERIZATION OF THE FACTORS INVOLVED IN THE REGULATION OF FAS I SYSTEM IN MYCOBACTERIA

GAGO, GABRIELA; GRAMAJO, HUGO; CABRUJA, MATÍAS

Buenos Aires

Congreso; Reunión Conjunta Sociedades de Biociencias de Argentina- LIII Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2017

SAIB

The genera Mycobacterium, which includes the causative agent of tuberculosis, unlike other microorganisms has two fatty acid synthase (FAS) systems, FAS I and FAS II, working in concert with the polyketide synthases (PKS) to produce a vast diversity of complex lipids. Briefly, FAS I performs the biosynthesis of acyl-CoAs de novo and FAS II elongates them to synthetize very long-chain meromycolyl-ACPs (up to C56), the precursors of mycolic acids. These mycolic acids are the main component of mycobacteria cell envelope and play an important role in the reduced cell wall permeability, virulence and acid fastness characteristic. Elucidation of the mechanisms involved in the regulation of fatty acid biosynthesis would shed light on the ability of M. tuberculosis to adapt and survive within the infected host.To study the interaction between the two FAS systems we constructed a conditional mutant of the fas gene in order to reduce the levels of this enzyme and consequently de novo fatty acid biosynthesis. Although we found that the expression of the fas gene was reduced, the production of mycolic acids was not inhibited. These results were obtained both analyzing de novo production of mycolic acid using radioactive acetate incorporation as well as mycolic acid accumulation by LC-MS experiments.We also performed a shotgun proteomic analysis in order to study the general protein expression profile responsible for the phenotype observed. We found that many proteins involved in the synthesis and assembly of mycolic acids in the envelope were upregulated when the levels of FAS I activity were reduced.We also found that the fatty acids necessary to synthesize mycolic acids were taken from TAG, a storage lipid produced by mycobacteria. In summary, we proved that when the fas gene expression is reduced mycobacteria uses TAG as an alternative source of fatty acids to synthetize mycolic acids but it is not able to synthesize phospholipids, leading to the arrest of the growth and lysis of the bacterium.