Structure, function, and inhibition of enoyl reductases

Abstract

Malaria and tuberculosis constitute two of the world’s deadliest infectious diseases. Together, they afflict over one third of the world’s population. Once thought of as one of a group of nearly vanquished diseases only 50 years ago, malaria and tuberculosis have experienced renewed prominence due to issues such as multi-drug resistance and a lack of responsiveness by the global community. Fatty acid biosynthesis has been shown to be an essential pathway to the causative organisms of malaria and tuberculosis. One integral component of the fatty acid biosynthesis pathway, enoyl acyl-carrier-protein (ACP) reductase, has repeatedly been validated as an appropriate drug target in other organisms. The 2.4 Å crystal structure of the enoyl-ACP reductase from the human parasite Plasmodium falciparum (PfENR) reveals a nucleotide-binding Rossmann fold, as well as the identity of several active site residues important for catalysis. The 2.43 Å crystal structure of PfENR bound with triclosan, a widely utilized anti-bacterial compound, provides new information concerning key elements of inhibitor binding. Applying knowledge attained from these initial crystal structures, several triclosan derivatives were synthesized, and subsequently PfENR:inhibitor co-crystal structures were determined to extend our knowledge of protein:inhibitor interactions within the active site. Additionally, the crystal structures of the enoyl-ACP reductase from the mouse parasite Plasmodium berghei (PbENR), in apo-form and in complex with triclosan, were refined to 2.9 Å and 2.5 Å resolution, respectively. These structures confirm the structural and active site conservation between the human and mouse parasite enoyl-ACP reductases, suggesting that utilizing a murine model for in vivo testing of promising inhibitors is viable. The 2.6 Å crystal structure of the enoyl-ACP reductase from Mycobacterium tuberculosis (InhA) in complex with triclosan reveals a novel configuration of triclosan binding, where two molecules of triclosan are accommodated within the InhA active site. Finally, high-throughput screening approaches using enoyl acyl-carrier-protein reductases as the targets were utilized to identify new lead compounds for future generations of drugs. The 2.7 Å crystal structure of InhA bound with Genz-10850 confirms the value of this technique.