Two classes of plant-like vacuolar-type H +-pyrophosphatases in malaria parasites

Abstract

In plants, cytosolic inorganic pyrophosphate (PP i) is hydrolyzed by energy-conserving vacuolar-type H +-pyrophosphatases (V-PPases) that harness the free energy of PP i hydrolysis to establish transmembrane H + gradients. Here we describe the identification and cloning of two genes, PfVP1 and PfVP2, from the malaria parasite Plasmodium falciparum. Inferred to encode type I (K +-dependent) and type II (K +-independent) V-PPases, respectively, PfVP1 and PfVP2 appeared more sequence divergent from each other than from their type I and type II counterparts in plants. The steady state levels of PfVP1 mRNA were high in comparison to PfVP2 mRNA throughout the erythrocytic phases of infection. Western analyses of trophozoite membranes using generic V-PPase antibodies (PAB HK and PAB TK) demonstrated appreciable amounts of a Mr 67 000 polypeptide whose associated aminomethylenediphosphonate- (AMDP) inhibitable PPase activity was markedly stimulated by K +. Immunofluorescence microscopy of infected erythrocytes revealed PfVP antigen associated with both the parasite plasma membrane and punctate intracellular inclusions. Transient transfection of a PfVP1– GFP fusion further supported the localization of PfVP1 to the parasite plasma membrane. Based on these findings and the growth-retarding effects of AMDP, P. falciparum is concluded to possess both type I and type II V-PPases of which the former has the greatest potential for contributing to the establishment of H + gradients across the parasite plasma membrane under conditions of energy limitation.