We report the cloning and sequencing of a gene encoding the farnesyl pyrophosphate synthase of Trypanosoma cruzi. The protein (T. cruzi farnesyl pyrophosphate synthase, TcFPPS) is an attractive target for drug development, since the growth of T. cruzi is inhibited by carbocation transition state/reactive intermediate analogs of its substrates, the nitrogen-containing bisphosphonates currently in use in bone resorption therapy. The protein predicted from the nucleotide sequence of the gene has 362 amino acids and a molecular mass of 41.2 kDa. Several sequence motifs found in other FPPSs are present in TcFPPS. Heterologous expression of TcF-PPS in Escherichia coli produced a functional enzyme that was inhibited by the nitrogen-containing bisphosphonates alendronate, pamidronate, homorisedronate, and risedronate but was less sensitive to the non-nitrogen-containing bisphosphonate etidronate, which, unlike the nitrogen-containing bisphosphonates, does not affect parasite growth. The protein contains a unique 11-mer insertion located near the active site, together with other sequence differences that may facilitate the development of novel anti-Chagasic agents.

Trypanosoma cruzi, the etiologic agent of Chagas disease, resists extreme fluctuations in osmolarity during its life cycle. T. cruzi possesses a robust regulatory volume decrease mechanism that completely reverses cell swelling when submitted to hypo-osmotic stress. The efflux of amino acids and K ؉ release could account for only part for this volume reversal. In this work we demonstrate that swelling of acidocalcisomes mediated by an aquaporin and microtubule-and cyclic AMP-mediated fusion of acidocalcisomes to the contractile vacuole complex with translocation of this aquaporin and the resulting water movement are responsible for the volume reversal not accounted for by efflux of osmolytes. Contractile vacuole bladders were isolated by subcellular fractionation in iodixanol gradients, showed a high concentration of basic amino acids and inorganic phosphate, and were able to transport protons in the presence of ATP or pyrophosphate. Taken together, these results strongly support a role for acidocalcisomes and the contractile vacuole complex in osmoregulation and identify a functional role for aquaporin in protozoal osmoregulation.

Typanosoma cruzi, the causative agent of Chagas disease, has recently been shown to be sensitive to the action of the bisphosphonates currently used in bone resorption therapy. These compounds target the mevalonate pathway by inhibiting farnesyl diphosphate synthase (farnesyl pyrophosphate synthase, FPPS), the enzyme that condenses the diphosphates of C5 alcohols (isopentenyl and dimethylallyl) to form C10 and C15 diphosphates (geranyl and farnesyl). The structures of the T. cruzi FPPS (TcFPPS) alone and in two complexes with substrates and inhibitors reveal that following binding of the two substrates and three Mg2+ ions, the enzyme undergoes a conformational change consisting of a hinge-like closure of the binding site. In this conformation, it would be possible for the enzyme to bind a bisphosphonate inhibitor that spans the sites usually occupied by dimethylallyl diphosphate (DMAPP) and the homoallyl moiety of isopentenyl diphosphate. This observation may lead to the design of new, more potent anti-trypanosomal bisphosphonates, because existing FPPS inhibitors occupy only the DMAPP site. In addition, the structures provide an important mechanistic insight: after its formation, geranyl diphosphate can swing without leaving the enzyme, from the product site to the substrate site to participate in the synthesis of farnesyl diphosphate.

We cloned an aquaporin gene from Trypanosoma cruzi (TcAQP) that encodes a protein of 231 amino acids, which is highly hydrophobic. The protein has six putative transmembrane domains and the two signature motifs asparagine-proline-alanine (NPA) which have been shown, in other aquaporins, to be involved in the formation of an aqueous channel spanning the bilayer. TcAQP was sensitive to endo H treatment, suggesting that the protein is N-glycosylated. Oocytes of Xenopus laevis expressing TcAQP swelled under hyposmotic conditions indicating water permeability, which was abolished after preincubating oocytes with very low concentrations of the AQP inhibitors HgCl 2 and AgNO 3 . No glycerol transport was detected. Immunofluorescence microscopy of T. cruzi expressing GFP-TcAQP showed co-localization of TcAQP with the vacuolar proton pyrophosphatase (V-H ؉ -PPase), a marker of acidocalcisomes. This localization was confirmed by Western blotting and immunofluorescence staining using polyclonal antibodies against a C-terminal peptide of TcAQP. In addition, there was a strong anterior labeling in a vacuole, close to the flagellar pocket, that was distinct from the acidocalcisomes and that was identified by immunogold electron microscopy as the contractile vacuole complex. Taking together, the presence of an aquaporin in acidocalcisomes and the contractile vacuole complex of T. cruzi, provides support for the role of these organelles in osmotic adaptations of these parasites.

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We report the cloning and sequencing of a gene encoding the farnesyl pyrophosphate synthase (FPPS) of Trypanosoma brucei. The protein (TbFPPS) is an attractive target for drug development because the growth of T. brucei has been shown to be inhibited by analogs of its substrates, the nitrogen containing bisphosphonates currently in use in bone resorption therapy. The protein predicted from the nucleotide sequence of the gene has 367 amino acids and a molecular mass of 42 kDa. Several sequence motifs found in other FPPSs are present in TbFPPS, including an 11-mer peptide insertion present also in the Trypanosoma cruzi FPPS. Heterologous expression of TbFPPS in Escherichia coli produced a functional enzyme that was inhibited by several nitrogencontaining bisphosphonates, such as pamidronate and risedronate. Risedronate was active in vivo against T. brucei infection in mice (giving a 60% survival rate), but pamidronate was not effective. The essential nature of TbFPPS was studied using RNA interference (RNAi) to inhibit the expression of the gene. Expression of TbF-PPS double-stranded RNA in procyclic trypomastigotes caused specific degradation of mRNA. After 4 days of RNAi, the parasite growth rate declined and the cells subsequently died. Similar results were obtained with bloodstream form trypomastigotes, except that the RNAi system in this case was leaky and mRNA levels and parasites recovered with time. Molecular modeling and structure-activity investigations of enzyme and in vitro growth inhibition data resulted in similar pharmacophores, further validating TbFPPS as the target for bisphosphonates. These results establish that FPPS is essential for parasite viability and validate this enzyme as a target for drug development.The Trypanosoma brucei group of parasites causes African trypanosomiasis (sleeping sickness) in humans, and nagana in animals and is responsible for heavy socioeconomic losses in most countries of sub-Saharan Africa (1). Therapy against African sleeping sickness is unsatisfactory because of the toxicity of currently available drugs, together with the development of drug resistance (2).A number of bisphosphonates have recently been shown to have significant activity against the proliferation of T. brucei and other parasites in vitro (3, 4) and also have curative effects in in vivo models of visceral (5) and cutaneous (6) leishmaniasis. Bisphosphonates are pyrophosphate analogs in which the oxygen bridge between the two phosphorus atoms has been replaced by a carbon substituted with various side chains. Several bisphosphonates are potent inhibitors of bone resorption and are in clinical use for the treatment and prevention of osteoporosis, Paget's disease, hypercalcemia caused by malignancy, and tumor metastases in bone (7-10). Many bisphosphonates, such as pamidronate, alendronate, and risedronate, are known to inhibit farnesyl pyrophosphate synthase (FPPS) 1 (11-16), and in so doing, they inhibit the formation of farnesyl pyrophosphate, a compound used in protein prenylation and in the syn...

We report the cloning of a Trypanosoma cruzi gene encoding a solanesyl-diphosphate synthase, TcSPPS. The amino acid sequence (molecular mass ϳ 39 kDa) is homologous to polyprenyl-diphosphate synthases from different organisms, showing the seven conserved motifs and the typical hydrophobic profile. TcSPPS preferred geranylgeranyl diphosphate as the allylic substrate. The final product, as determined by TLC, had nine isoprene units. This suggests that the parasite synthesizes mainly ubiquinone-9 (UQ-9), as described for Trypanosoma brucei and Leishmania major. In fact, that was the length of the ubiquinone extracted from epimastigotes, as determined by high-performance liquid chromatography. Expression of TcSPPS was able to complement an Escherichia coli ispB mutant. A punctuated pattern in the cytoplasm of the parasite was detected by immunofluorescence analysis with a specific polyclonal antibody against TcSPPS. An overlapping fluorescence pattern was observed using an antibody directed against the glycosomal marker pyruvate phosphate dikinase, suggesting that this step of the isoprenoid biosynthetic pathway is located in the glycosomes. Co-localization in glycosomes was confirmed by immunogold electron microscopy and subcellular fractionation. Because UQ has a central role in energy production and in reoxidation of reduction equivalents, TcSPPS is promising as a new chemotherapeutic target.

We investigated the molecular basis of the activity of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the etiological agent of Chagas' disease. We found that growth inhibition of T. cruzi epimastigotes induced by this compound was associated with a reduction in the content of the parasite's endogenous sterols due to a specific blockade of their de novo synthesis at the level of squalene synthase.There is an urgent need for safer and more potent drugs for the specific treatment of Chagas' disease, the largest parasitic disease burden in Latin America. Currently available drugs have serious limitations due to limited efficacy, particularly in the chronic stage of the disease, and frequent toxic side effects (25). The etiological agent of Chagas' disease, the kinetoplastid protozoan Trypanosoma cruzi, has a complex life cycle with proliferative and infective stages in both its insect (Reduviidae) vectors and mammalian hosts, where the parasite develops intracellularly, leading to tissue damage compounded by the ensuing inflammatory response (2). There are 16 to 18 million people already infected in Latin America. Most of them are in the chronic stage of the disease, in which 30 to 40% will develop serious, often lethal, cardiac and gastrointestinal tract lesions (7, 25).We have recently described the potent and selective in vitro activity of 4-phenoxyphenoxy and aryloxyethyl derivatives against both the extracellular epimastigote and the clinically relevant intracellular amastigote forms of T. cruzi, but the molecular mechanisms of these effects remained unclear (4, 8).T. cruzi and related trypanosomatid parasites have a strict requirement for specific endogenous sterols (ergosterol and analogs) for survival and growth and cannot use the abundant supply of cholesterol present in their mammalian hosts (14-17). We have shown that ergosterol biosynthesis inhibitors with potent in vitro activity and special pharmacokinetic properties in mammals (large volumes of distribution and long half-lives) can induce radical parasitological cure in animal models of both acute and chronic experimental Chagas' disease (14-18). We decided to investigate the possible effect of 4-phenoxyphenoxyethylthiocyanate (WC-9), the most potent member of this group of compounds, on the de novo sterol biosynthesis in intact T. cruzi epimastigotes, because previous work indicated interference by this type of compounds with steroid biogenesis in mammals (22,23).WC-9 induced a dose-dependent effect on growth of the epimastigote form of the EP strain of parasite (Fig. 1). When the EP strain was grown in liver infusion tryptose (LIT) me-