Enoyl ACP reductase

The final step in each round of fatty acyl elongation in E. coli is the NADH-dependent reduction of the trans double bond, catalyzed by the homotetrameric (subunit mass of 29 kDa) NADH-dependent enoyl-ACP reductase I (encoded by fabl). The Fabl amino acid sequence is similar (34% identical) to the product of a gene (called inhA) from mycobacteria. InhA is involved in mycolic acid biosynthesis (A. Banerjee, 1994). The synthesis of these unusual 70-80 carbon mycobacterial acids requires a pathway composed of enzymes essentially identical to those of fatty acid synthesis. Missense mutations within the inhA gene result in resistance to the anti-tuberculosis drugs, isoniazid and ethionamide. The crystal structures of Fabl and InhA have been solved, and are virtually superimposable for most 

---

Sharma SK, Kumar G Kappoor M, Suroli A. (2008) Combined effect of epi-gallocatechin gallate and triclosan on enoyl-ACP reductases of Mycobacterium tuberculosis. Biochem Biophys Res Commun 368 7-12. 

ENOYL-ACP REDUCTASE FATTYACID SYNTHETASE ENOYL-CoA HYDRATASE (or, CROTONASE) ENOYLPYRUVATE Enrichment,... 

Figure 3.8 One complete cycle and the first step in the next cycle of the events during the synthesis of fatty acids. ACP = acyl carrier protein, a complex of six enzymes i.e. acetyl CoA-ACP transacetylase (AT) malonyl CoA-ACP transferase (MT) /3-keto-ACP synthase (KS) /J-ketoacyl-ACP reductase (KR) / - hydroxyacyl-ACP-dehydrase (HD) enoyl-ACP reductase (ER).

Step (4) Reduction of the Double Bond Finally the double bond of 1/rm.s-A2-butenoyl-ACP is reduced (saturated) to form butyryl-ACP by the action of enoyl-ACP reductase (ER) again, NADPH is the electron donor. 

A second reduction step occurs. Domain Enoyl-ACP reductase t... 

The Reduction Reactions. The object of the next three reactions (steps 4 to 6 in fig. 18.12a) is to reduce the 3-carbonyl group to a methylene group. The carbonyl is first reduced to a hydroxyl by 3-ketoacyl-ACP reductase. Next, the hydroxyl is removed by a dehydration reaction catalyzed by 3-hydroxyacyl-ACP dehydrase with the formation of a trans double bond. This double bond is reduced by NADPH catalyzed by 2,3-trans-enoyl-ACP reductase. Chemically, these reactions are nearly the same as the reverse of three steps in the j6-oxidation pathway except that the hydroxyl group is in the D-configuration for fatty acid synthesis and in the L-configuration for /3 oxidation (compare figs. 18.4a and 18.12a). Also remember that different cofactors, enzymes and cellular compartments are used in the reactions of fatty acid biosynthesis and degradation. 

Reduction of crotonyl-ACP by a second NADPH molecule to give butyryl-ACP (catalyzed by enoyl-ACP reductase). 

Liu N, Cummings JE, England Ket al (2011) Mechanism and inhibition of the FabI enoyl-ACP reductase from Burkholderia pseudomallei. J Antimicrob Chemother 66 564-573... 

Tipparaju SK, Mulhearn DC, Klein GM et al (2008) Design and synthesis of aryl ether inhibitors of the Bacillus anthracis enoyl-ACP reductase. ChemMedChem 3 1250-1268... 

The last step in the fatty acid biosynthetic pathway is catalyzed by enoyl-acyl carrier protein (ACP) reductase, which is responsible for reduction of the double bond in the enoyl-ACP derivative (Heath and Rock, 1995 Payne et al., 2002). While fabl genes encode enoyl-ACP reductases (FabI enzymes) in S. aureus and E. coli, an alternative enoyl-ACP reductase, FabK, replaces the function of Fabl in a number of bacterial species such as Streptococcus pneumoniae (Heath and Rock, 2000). More interestingly, a number of bacterial species (such as Enterococcus faecalis and Pseudomonas aeruginosa) possess both the Fabl and FabK enzymes (Heath and Rock, 2000). To discover Fabl-specific antibacterial inhibitors, Payne and colleagues at GlaxoSmithKline (GSK) developed assays for various versions of enoyl-ACP reductases (Payne et al., 2002 Seefeld et al., 2003) based on the following reaction scheme ... 

Miller, W.H. et al. 2002. Discovery of aminopyridine-based inhibitors of bacterial enoyl-ACP reductase (FabI). J. Med. Chem. 45, 3246-3256. 

Seefeld, M.A. et al. 2003. Indole naphthyridinones as inhibitors of bacterial enoyl-ACP reductases FabI and FabK. J. Med Chem. 46, 1627-1635. 

Quemard A, Dessen A, Sugantino M, Jacobs MR Jr, Sacchettini JC, Blanchard JS. Binding of catalase-peroxidase-activated isoniazid to wild-type and mutant Mycobacterium tuberculosis enoyl-ACP reductases. J. Am. Chem. Soc. 1996 118 1561-1562. 

This four-step cycle includes condensation of acetate and malonate to give ketobu-tanoate with subsequent reduction to butanoate in three further steps. These are reduction to the 3R hydroxy acid, dehydration to the 2t acid, and reduction again. Reduction is affected by NADPH and a proton. The process is then repeated to add further two-carbon units until a thioesterase liberates the free acid. This sequence requires a fatty acid synthase, which contains the enzymes needed for each of the four steps viz. p-ketoacyl-ACP synthase, p-ketoacyl-ACP reductase, p-ketoacyl-ACP dehydrase, and enoyl-ACP reductase, respectively. 

The enoyl is then reduced with NADPH substituting for FADH2 (Enoyl-ACP reductase) to give the saturated acyl group. 

Enoyl-ACP reductase catalyzes the second reduction with NADPH. 

Crotonyl ACP -P NADPH -P H > butyryl ACP -P NADP Enoyl ACP reductase... 

Bonnac, L., Gao, G.Y., Chen, L., et al. (2007) Synthesis of 4-phenoxybenzamide adenine dinucleotide as NAD analogue with inhibitory activity against enoyl-ACP reductase (InhA) of Mycobacterium tuberculosis. Bioorg. Med. Chem. Lett. 17, 4588 591. 

Surolia, N., and Surolia, A. (2001). Triclosan offers protection against blood stages of malaria by inhibiting enoyl-ACP reductase of Plasmodium falciparum. Nat. Med. 7,167-173. 

---