Recombinant Plasmodium falciparum NADP-dependent isocitrate dehydrogenase is active and harbours a unique 26 amino acid tail

During infection, Plasmodium spp. require reducing equivalents such as NADPH to support the function of specific enzymes in overcoming oxidative stress. The catalysis of isocitrate by the NADP-dependent isocitrate dehydrogenase of Plasmodium falciparum (pfICDH) generates NADPH and is thus crucial for the parasite’s survival and pathogenecity. In this study, pfICDH was cloned from a clinical isolate of P. falciparum. This was facilitated by designing primers based on the P. falciparum genome sequence resource PlasmoDB. DNA sequence of the cloned gene revealed an ORF that encodes a protein of 468 aa. Furthermore, after expression in Esherichia coli BL21, enzyme assays of cell-free extracts confirmed the overexpression and function of pfICDH. Further, pfICDH purified by affinity chromatography retained its enzyme activity. Substitution of NADP for NAD, or the use of EDTA, in enzyme assays abolished pfICDH activity. ATP and chloroquine, as well as cupric and argentic ions, inhibited pfICDH activity. Phylogenetic analysis revealed high primary structure homology (45–97%) among genes coding for eukaryal NADP-dependent ICDH, and the occurrence of three subfamilies of ICDH genes. Interestingly, there were significant sequence dissimilarities between pfICDH and its mammalian or bacterial homologs, particularly at the N- and C-termini. Confirming the functionality of the cloned pfICDH, and asserting its distance from the human homolog by molecular definitions, are important prerequisites for promoting this gene as a drug target screen. Index Descriptors and Abbreviations: ICDH, isocitrate dehydrogenase; pfICDH, Plasmodium falciparum ICDH; NADPH, β-nicotinamide adenine dinucleotide phosphate reduced; NADP, β-nicotinamide adenine dinucleotide; GST, gluthathione- S-transferase; ORF, open-reading frame