Molecular organization and physiological functions of the respiratory chain specific for mitochondria from Plasmodium

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1. Studies on the respiratory chain specific for mitochondria from PlasmodiumThe mitochondrion and the apicoplast of the malaria parasite, Plasmodium spp is microscopically observed in a close proximity to each other. In this study, we tested the suitability of two different separation techniques-Percoll density gradient centrifugation and fluorescence-activated organelle sorting for improving the purity of mitochondria isolated from the crude organelle preparation of P falciparum. To our surprise, the apicoplast was inseparable from the plasmodial mitochondrion by each method. This implies these two plasmodial organelles are bound each other. This is the first experimental evidence of a physical binding between the two organelles in Plasmodium.2. Studies on cyanide-resistant alternative oxidases from parasitic protozoa and its spescific inhibitor, ascofuranoneBased on amino acid sequence similarity and the ability to catalyze the four-electron reduction of oxygen to water using a quin … More ol substrate, mitochondrial alternative oxidase (AOX) and plastid terminal oxidase (PTOX) appear to be two closely related members of the membrane-bound diiron carboxylate group of proteins. In the current studies, we took advantage of the high activity of Trypanosoma vivax AOX (TvAOX) to examine the importance of the conserved Glu and the Tyr residues around the predicted third helix region of AOXs and PTOXs. We first compared the amino acid sequences of TvAOX with AOXs and PTOXs from various taxa and then performed alanine-scanning mutagenesis of TvAOX between amino acids Y199 and Y247. We found that the ubiquinol oxidase activity of TvAOX is completely lost in the E214A mutant, whereas mutants E215A and E216A retained more than 30% of the wild-type activity. Among the Tyr mutants, a complete loss of activity was also observed for the Y221A mutant, whereas the activities were equivalent to wild-type for the Y199A, Y212A, and Y247A mutants. Finally, residues G1u214 and Tyr221 were found to be strictly conserved among AOXs and PTOXs. Based on these findings, it appears that AOXs and PTOXs are a novel subclass of diiron carboxylate proteins that require the conserved motif E(X)eY for enzyme activity. Less