Abstract 1150 Determination of Potential Novel Inhibitors for Francisella tularensis enoyl-acyl carrier protein reductase I (FabI) via High-Throughput Virtual Screening Methods

Tularemia, caused by the bacteria, Francisella tularensis, is a highly infectious disease transmitted primarily through ticks, mites, and mosquitos. When left untreated, the mortality rate ranges from 30%-60%. Due to Francisella tularensis virulence, it has been stockpiled and researched for its role as bioweapon. Enoyl-acyl carrier protein reductase, FabI, is an essential oxidoreductase enzyme for the last step of bacterial fatty acid elongation. The biological necessity of fatty acid biosynthesis and the absence of FabI proteins in humans makes them excellent anti-bacterial targets. In this work, high-throughput computational ligand docking programs such as GOLD (Genetic Optimization of Ligand Docking) and ICM (Internal Coordinate Mechanics) were utilized to identify potential novel inhibitors of the Francisella tularensis FabI enzyme (FtFabI). Over one hundred thousand ligands from diverse drug libraries were screened against an X-ray crystallography structure of FtFabI (PBD ID: 3NRC) in the enoyl-ACP site using both GOLD and ICM, generating a list of docking scores based on physico-chemical interactions. From Gold results, compounds ZINC-55 and ZINC-11 scored fifty percent better than the crystallized ligand, TCL. From ICM, compounds ICM-006 and ICM-028 scored twice as well relative to TCL. To validate virtual predictions, recombinant FtFabI protein with an 6-His Tag modification was expressed via autoinduction in BL21(DE3) cells and purified through nickel affinity chromatography. The purity of the protein was verified via SDS-page gel characterization by confirmation of a 29 kDa band. Differential Scanning Fluorimetry (DSF) was used to determine the melting temperature of apo FtFabI to be 53°C. The several promising compounds from virtual screening were assayed against FtFabI via DSF to empirically validate their binding potential. Novel inhibitors from this study may lead to specific, small-molecule drug treatment of Francisella Tularensis infection.