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Báo cáo khoa học: Analyses of co-operative transitions inPlasmodium falciparumb-ketoacyl acyl carrier protein reductase upon co-factor and acyl carrier protein binding

The type II fatty acid synthase pathway ofPlasmodium falciparumis a validated unique target for developing novel antimalarials because of its intrinsic differences from the type I pathway operating in humans. b-Ketoacyl-acyl carrier protein reductase is the only enzyme of this pathway that has no isoforms and thus selective inhibitors can be developed for this player of the pathway. | sFEBS Journal Analyses of co-operative transitions in Plasmodium falciparum b-ketoacyl acyl carrier protein reductase upon co-factor and acyl carrier protein binding Krishanpal Karmodiya and Namita Surolia Molecular Biology and Genetics Unit JawaharlalNehru Centre for Advanced Scientific Research Jakkur Bangalore India Keywords b-ketoacyl-ACP reductase cofactor conformationalchange fluorescence quenching Plasmodium Correspondence N. Surolia Molecular Biology and Genetics Unit JawaharlalNehru Centre for Advanced Scientific Research Jakkur Bangalore-560064 India Fax 91 80 22082766 Tel 91 80 22082820 21 E-mail surolia@jncasr.ac.in Received 12 April2006 revised 15 June 2006 accepted 10 July 2006 doi 10.1111 j.1742-4658.2006.05412.x The type II fatty acid synthase pathway of Plasmodium falciparum is a validated unique target for developing novel antimalarials because of its intrinsic differences from the type I pathway operating in humans. b-Ketoacyl-acyl carrier protein reductase is the only enzyme of this pathway that has no isoforms and thus selective inhibitors can be developed for this player of the pathway. We report here intensive studies on the direct interactions of Plasmodium b-ketoacyl-acyl carrier protein reductase with its cofactor NADPH acyl carrier protein acetoacetyl-coenzyme A and other ligands in solution by monitoring the intrinsic fluorescence kmax 334 nm of the protein as a result of its lone tryptophan as well as the fluorescence of NADPH kmax 450 nm upon binding to the enzyme. Binding of the reduced cofactor makes the enzyme catalytically efficient as it increases the binding affinity of the substrate acetoacetyl-coenzyme A by 16-fold. The binding affinity of acyl carrier protein to the enzyme also increases by approximately threefold upon NADPH binding. Plasmodium b-ketoacyl-acyl carrier protein reductase exhibits negative homotropic co-operative binding for NADPH which is enhanced in the presence of acyl carrier protein. Acyl carrier protein .