Slow-tight binding inhibition of enoyl-acyl carrier protein reductase from Plasmodium falciparum by triclosan

Kapoor, Mili and Reddy, Chandramouli C and Krishnasastry, MV and Surolia, Namita and Surolia, Avadhesha (2004) Slow-tight binding inhibition of enoyl-acyl carrier protein reductase from Plasmodium falciparum by triclosan. In: Biochemical Journal, 381 . pp. 719-724.

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Abstract

Triclosan is a potent inhibitor of FabI (enoyl-ACP reductase, where ACP stands for acyl carrier protein), which catalyses the last step in a sequence of four reactions that is repeated many times with each elongation step in the type II fatty acid biosynthesis pathway. The malarial parasite Plasmodium falciparum also harbours the genes and is capable of synthesizing fatty acids by utilizing the enzymes of type II FAS (fatty acid synthase). The basic differences in the enzymes of type I FAS, present in humans, and type II FAS, present in Plasmodium, make the enzymes of this pathway a good target for antimalarials. The steady-state kinetics revealed time-dependent inhibition of FabI by triclosan, demonstrating that triclosan is a slow-tight-binding inhibitor of FabI. The inhibition followed a rapid equilibrium step to form a reversible enzyme-inhibitor complex (EI) that isomerizes to a second enzyme-inhibitor complex (EI*), which dissociates at a very slow rate. The rate constants for the isomerization of EI to EI* and the dissociation of EI* were 5.49 x $10^{\mathrm{-2}}$ and 1 x $10^{\mathrm{-4}}$ $s^{\mathrm{-1}}$ respectively. The $K_{i}$ value for the formation of the EI complex was 53nM and the overall inhibition constant $K_{i}$* was 96 pM. The results match well with the rate constants derived independently from fluorescence analysis of the interaction of FabI and triclosan, as well as those obtained by surface plasmon resonance studies.

Item Type:	Journal Article
Publication:	Biochemical Journal
Publisher:	Portland Press
Additional Information:	Copyright for this article belongs to Portland Press
Keywords:	Enoyl-ACP reductase;crotonoyl-coenzyme A;Plasmodium falciparum;triclosan;fatty acid biosynthesis;slow-tight binding inhibitor
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	25 Oct 2004
Last Modified:	19 Sep 2010 04:16
URI:	http://eprints.iisc.ac.in/id/eprint/2124

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