The emergence of drug-resistant forms of Plasmodium falciparum emphasizes the need to develop new
antimalarials. In this context, the
fatty acid biosynthesis (FAS) pathway of the malarial parasite has recently received a lot of attention. Due to differences in the
fatty acid biosynthesis systems of Plasmodium and man, this pathway is a good target for the development of new and selective therapeutic drugs directed against
malaria. In continuation of these efforts we report cloning and overexpression of P. falciparum beta-hydroxyacyl-
acyl carrier protein (ACP)
dehydratase (PffabZ) gene that codes for a 17-kDa
protein. The
enzyme catalyzes the
dehydration of beta-hydroxyacyl-ACP to trans-2-acyl-ACP, the third step in the elongation phase of the FAS cycle. It has a Km of 199 microM and kcat/Km of 80.4 m-1 s-1 for the substrate analog
beta-hydroxybutyryl-CoA but utilizes crotonoyl-
CoA, the product of the reaction, more efficiently (Km = 86 microM, kcat/Km = 220 m-1 s-1). More importantly, we also identify inhibitors (NAS-91 and NAS-21) for the
enzyme. Both the inhibitors prevented the binding of crotonoyl-
CoA to PfFabZ in a competitive fashion. Indeed these inhibitors compromised the growth of P. falciparum in cultures and inhibited the parasite
fatty acid synthesis pathway both in cell-free extracts as well as in situ. We modeled the structure of PfFabZ using Escherichia coli beta-hydroxydecanoyl thioester
dehydratase (EcFabA) as a template. We also modeled the inhibitor complexes of PfFabZ to elucidate the mode of binding of these compounds to FabZ. The discovery of the inhibitors of FabZ, reported for the first time against any member of this family of
enzymes, essential to the type II FAS pathway opens up new avenues for treating a number of
infectious diseases including
malaria.