Targeting The Enoyl-Reductase Enzyme (Fabi): Modern Drug Discovery Effects To Combat Tularemia

Francisella tularensis is a highly virulent and contagious gram‐negativeintracellular bacterium that causes the disease tularemia in mammals. The high infectivity and the ability of the bacteriumto survive for weeks in a cool, moist environment have raisedthe possibility that this organism can be exploited deliberatelyas a potential biological weapon. Fatty acid synthesis (FAS) is essential for bacterial viability and it has also been validatedas an attractive target for the discovery of novel antibacterials. We have successfully cloned, overexpressed and purified the F. tularensis FAS enoyl reductase enzyme FabI (ftuFabI) and fully characterized the reaction mechanism through steady‐state kinetics. Based on the 2.5Å resolution crystal structure we firstly resolved and pre‐steady state kinetics, a two‐step mechanism coupled to ordering of the active site loop was proposed for inhibition of the enzyme by triclosan. We also identified a series of diphenyl ethers which are subnanomolar inhibitors of the enzyme and that inhibit bacterial growth with MIC 90 values as low as 0.09 μg/ml. One of these promising compounds is active in a mouse model of tularemia infection.