Evidence for the role of vacuolar soluble pyrophosphatase and inorganic polyphosphate in Trypanosoma cruzi persistence

Inorganic Polyphosphate Is in the Surface of Trypanosoma cruzi but Is Not Significantly Secreted

Trypanosoma cruzi is the etiologic agent of Chagas disease, an infection that can lead to the development of cardiac fibrosis, which is characterized by the deposition of extracellular matrix (ECM) components in the interstitial region of the myocardium. The parasite itself can induce myofibroblast differentiation of cardiac fibroblast in vitro, leading to increased expression of ECM. Inorganic polyphosphate (polyP) is a linear polymer of orthophosphate that can also induce myofibroblast differentiation and deposition of ECM components and is highly abundant in T. cruzi. PolyP can modify proteins post-translationally by non-enzymatic polyphosphorylation of lysine residues of poly-acidic, serine-(S) and lysine (K)-rich (PASK) motifs. In this work, we used a bioinformatics screen and identified the presence of PASK domains in several surface proteins of T. cruzi. We also detected polyP in the external surface of its different life cycle stages and confirmed the stimulation of host cell fibrosis by trypomastigote infection. However, we were not able to detect significant secretion of the polymer or activation of transforming growth factor beta (TGF-β), an important factor for the generation of fibrosis by inorganic polyP- or trypomastigote-conditioned medium.

Advances in the cellular biology, biochemistry, and molecular biology of acidocalcisomes

SUMMARYAcidocalcisomes are organelles conserved during evolution and closely related to the so-called volutin granules of bacteria and archaea, to the acidocalcisome-like vacuoles of yeasts, and to the lysosome-related organelles of animal species. All these organelles have in common their acidity and high content of polyphosphate and calcium. They are characterized by a variety of functions from storage of phosphorus and calcium to roles in Ca2+ signaling, osmoregulation, blood coagulation, and inflammation. They interact with other organelles through membrane contact sites or by fusion, and have several enzymes, pumps, transporters, and channels.

Transcriptomic analysis of the adaptation to prolonged starvation of the insect-dwelling Trypanosoma cruzi epimastigotes

Trypanosoma cruzi is a digenetic unicellular parasite that alternates between a blood-sucking insect and a mammalian, host causing Chagas disease or American trypanosomiasis. In the insect gut, the parasite differentiates from the non-replicative trypomastigote forms that arrive upon blood ingestion to the non-infective replicative epimastigote forms. Epimastigotes develop into infective non-replicative metacyclic trypomastigotes in the rectum and are delivered via the feces. In addition to these parasite stages, transitional forms have been reported. The insect-feeding behavior, characterized by few meals of large blood amounts followed by long periods of starvation, impacts the parasite population density and differentiation, increasing the transitional forms while diminishing both epimastigotes and metacyclic trypomastigotes. To understand the molecular changes caused by nutritional restrictions in the insect host, mid-exponentially growing axenic epimastigotes were cultured for more than 30 days without nutrient supplementation (prolonged starvation). We found that the parasite population in the stationary phase maintains a long period characterized by a total RNA content three times smaller than that of exponentially growing epimastigotes and a distinctive transcriptomic profile. Among the transcriptomic changes induced by nutrient restriction, we found differentially expressed genes related to managing protein quality or content, the reported switch from glucose to amino acid consumption, redox challenge, and surface proteins. The contractile vacuole and reservosomes appeared as cellular components enriched when ontology term overrepresentation analysis was carried out, highlighting the roles of these organelles in starving conditions possibly related to their functions in regulating cell volume and osmoregulation as well as metabolic homeostasis. Consistent with the quiescent status derived from nutrient restriction, genes related to DNA metabolism are regulated during the stationary phase. In addition, we observed differentially expressed genes related to the unique parasite mitochondria. Finally, our study identifies gene expression changes that characterize transitional parasite forms enriched by nutrient restriction. The analysis of the here-disclosed regulated genes and metabolic pathways aims to contribute to the understanding of the molecular changes that this unicellular parasite undergoes in the insect vector.

New insights into the role of acidocalcisomes in trypanosomatids

Acidocalcisomes are electron-dense organelles rich in polyphosphate and inorganic and organic cations that are acidified by proton pumps, and possess several channels, pumps, and transporters. They are present in bacteria and eukaryotes and have been studied in greater detail in trypanosomatids. Biogenesis studies of trypanosomatid acidocalcisomes found that they share properties with lysosome-related organelles of animal cells. In addition to their described roles in autophagy, cation and phosphorus storage, osmoregulation, pH homeostasis, and pathogenesis, recent studies have defined the role of these organelles in phosphate utilization, calcium ion (Ca2+ ) signaling, and bioenergetics, and will be the main subject of this review.

Unusual features and localization of the membrane kinome of Trypanosoma brucei

In many eukaryotes, multiple protein kinases are situated in the plasma membrane where they respond to extracellular ligands. Ligand binding elicits a signal that is transmitted across the membrane, leading to activation of the cytosolic kinase domain. Humans have over 100 receptor protein kinases. In contrast, our search of the Trypanosoma brucei kinome showed that there were only ten protein kinases with predicted transmembrane domains, and unlike other eukaryotic transmembrane kinases, seven are predicted to bear multiple transmembrane domains. Most of the ten kinases, including their transmembrane domains, are conserved in both Trypanosoma cruzi and Leishmania species. Several possess accessory domains, such as Kelch, nucleotide cyclase, and forkhead-associated domains. Surprisingly, two contain multiple regions with predicted structural similarity to domains in bacterial signaling proteins. A few of the protein kinases have previously been localized to subcellular structures such as endosomes or lipid bodies. We examined the localization of epitope-tagged versions of seven of the predicted transmembrane kinases in T. brucei bloodstream forms and show that five localized to the endoplasmic reticulum. The last two kinases are enzymatically active, integral membrane proteins associated with the flagellum, flagellar pocket, or adjacent structures as shown by both fluorescence and immunoelectron microscopy. Thus, these kinases are positioned in structures suggesting participation in signal transduction from the external environment.

The IP3 receptor and Ca2+ signaling in trypanosomes

Trypanosoma cruzi, and the T. brucei group of parasites cause neglected diseases that affect millions of people around the world. These unicellular microorganisms have complex life cycles involving an insect vector and a mammalian host. Both groups of pathogens possess an inositol 1,4,5-trisphosphate (IP₃)/diacylglycerol (DAG) signaling pathway, and an IP₃ receptor, but with lineage-specific adaptations that make them different from their mammalian counterparts. The phospholipase C (PLC), which hydrolyzes phosphatidyl inositol 4,5-bisphosphate (PIP₂) to IP₃ is N-terminally myristoylated and palmitoylated. Acidocalcisomes, which are lysosome-related organelles rich in polyphosphate, are the main intracellular Ca²⁺ stores. The inositol 1,4,5-trisphosphate receptor (IP₃R) localizes to acidocalcisomes instead of the endoplasmic reticulum. The trypanosome IP₃R is stimulated by luminal phosphate and pyrophosphate, which are hydrolysis products of polyphosphate (polyP), and inhibited by tripolyphosphate (polyP₃), which is the most abundant polyP in acidocalcisomes. Ca²⁺ signaling is important for host cell invasion and differentiation and to maintain cellular bioenergetics.

Backbone resonance assignment and dynamics of 110 kDa hexameric inorganic pyrophosphatase from Mycobacterium tuberculosis

Family I soluble inorganic pyrophosphatases (PPases; EC 3.6.1.1) are enzymes essential for all organisms. They hydrolyze inorganic pyrophosphate, thus providing the driving force for numerous biosynthetic reactions. Soluble PPases retain enzymatic activity only in multimeric forms. PPases from various organisms are extensively studied by X-ray crystallography but until now there was no information on their structure and dynamics in solution. Hexameric 110 kDa (6 × 18.3 kDa) PPase from Mycobacterium tuberculosis (Mt-PPase) is a promising target for the rational design of potential anti-tuberculosis agents. In order to use NMR techniques in functional studies of Mt-PPase and rational design of the inhibitors for this enzyme, it is necessary to have information on the backbone ¹H, ¹³C and ¹⁵N resonance assignments. Samples of Mt-PPase enriched with 99% of ¹³C and ¹⁵N isotopes, and 95% of ²H were obtained using recombinant protein expression in an isotopically-labeled medium and effective heat-shock protocol for the deuterium-to-hydrogen exchange of the amide groups. Backbone resonance assignment was achieved for more than 95% of the residues. It was found that the secondary structure of Mt-PPase in solution corresponds well to the crystal structure of this protein. Protein backbone dynamics were studied using ¹⁵N NMR relaxation experiments. Determined resonance assignments and dynamic properties provide the basis for the subsequent structure-based design of novel inhibitors of Mt-PPase-potential anti-tuberculosis drugs.

Inorganic pyrophosphatase from the red flour beetle (Tribolium castaneum) modulates mitochondrial polyphosphate metabolism

Polyphosphates (polyPs) have been found in all cell types examined to date and play diverse roles, depending on the cell type. In eukaryotic organisms, polyPs have been mainly investigated in mammalian cells, with few studies on insects. In this study, we investigated mitochondrial polyphosphate metabolism in the red flour beetle, Tribolium castaneum. Substrate specificity for different chain lengths demonstrated the presence of two exopolyphosphatase isoforms in mitochondria. T. castaneum mitochondrial polyP levels decreased after injection with soluble pyrophosphatase (Tc-sPPase) dsRNA, while the membrane exopolyphosphate activity increased. Mitochondrial respiration modulated exopolyphosphatase activity only in wild-type beetles. Tripolyphosphate was able to increase the F-ATPase activity in wild-type and Tc-sPPase RNAi beetles. We suggest that inorganic pyrophosphatase modulates polyphosphate metabolism in mitochondria and affects the link between mitochondrial activity and polyphosphate metabolism in T. castaneum.

The acidocalcisome inositol-1,4,5-trisphosphate receptor of Trypanosoma brucei is stimulated by luminal polyphosphate hydrolysis products

Acidocalcisomes are acidic calcium stores rich in polyphosphate (polyP) and are present in trypanosomes and also in a diverse range of other organisms. Ca²⁺ is released from these organelles through a channel, inositol 1,4,5-trisphosphate receptor (TbIP₃R), which is essential for growth and infectivity of the parasite Trypanosoma brucei However, the mechanism by which TbIP₃R controls Ca²⁺ release is unclear. In this work, we expressed TbIP₃R in a chicken B lymphocyte cell line in which the genes for all three vertebrate IP₃Rs were stably ablated (DT40-3KO). We show that IP₃-mediated Ca²⁺ release depends on Ca²⁺ but not on ATP concentration and is inhibited by heparin, caffeine, and 2-aminomethoxydiphenyl borate (2-APB). Excised patch clamp recordings from nuclear membranes of DT40 cells expressing only TbIP₃R disclosed that luminal inorganic orthophosphate (P_i) or pyrophosphate (PP_i), and neutral or alkaline pH can stimulate IP₃-generated currents. In contrast, polyP or acidic pH did not induce these currents, and nuclear membranes obtained from cells expressing rat IP₃R were unresponsive to polyP or its hydrolysis products. Our results are consistent with the notion that polyP hydrolysis products within acidocalcisomes or alkalinization of their luminal pH activate TbIP₃R and Ca²⁺ release. We conclude that TbIP₃R is well-adapted to its role as the major Ca²⁺ release channel of acidocalcisomes in T. brucei.

Inorganic polyphosphate, a multifunctional polyanionic protein scaffold

Polyphosphate (polyP) consists of a linear arrangement of inorganic phosphates and defies its structural simplicity with an astounding number of different activities in the cell. Already well known for its ability to partake in phosphate, calcium, and energy metabolism, polyP recently gained a new functional dimension with the discovery that it serves as a stabilizing scaffold for protein-folding intermediates. In this review, we summarize and discuss the recent studies that have identified polyP not only as a potent protein-like chaperone that protects cells against stress-induced protein aggregation, but also as a robust modifier of amyloidogenic processes that shields neuronal cells from amyloid toxicity. We consider some of the most pressing questions in the field, the obstacles faced, and the potential avenues to take to provide a complete picture about the working mechanism and physiological relevance of this intriguing biopolymer.

Degradation of phosphate polymer polyP enhances lactic fermentation in mice

In bacteria, a polymer of inorganic phosphate (Pi) (inorganic polyphosphate; polyP) is enzymatically produced and consumed as an alternative phosphate donor for adenosine triphosphate (ATP) production to protect against nutrient starvation. In vertebrates, polyP has been dismissed as a "molecular fossil" due to the lack of any known physiological function. Here, we have explored its possible role by producing transgenic (TG) mice widely expressing Saccharomyces cerevisiae exopolyphosphatase 1 (ScPPX1), which catalyzes hydrolytic polyP degradation. TG mice were produced and displayed reduced mitochondrial respiration in muscles. In female TG mice, the blood concentration of lactic acid was enhanced, whereas ATP storage in liver and brain tissues was reduced significantly. Thus, we suggested that the elongation of polyP reduces the intracellular Pi concentration, suppresses anaerobic lactic acid production, and sustains mitochondrial respiration. Our results provide an insight into the physiological role of polyP in mammals, particularly in females.

Importance of polyphosphate in the Leishmania life cycle

Protozoan parasites contain negatively charged polymers of a few up to several hundreds of phosphate residues. In other organisms, these poly-phosphate (polyP) chains serve as an energy source and phosphate reservoir, and have been implicated in adaptation to stress and virulence of pathogenic organisms. In this study, we confirmed first that the polyP polymerase vacuolar transporter chaperone 4 (VTC4) is responsible for polyP synthesis in Leishmania parasites. During Leishmaniain vitro culture, polyP is accumulated in logarithmic growth phase and subsequently consumed once stationary phase is reached. However, polyP is not essential since VTC4-deficient (vtc4^-) Leishmania proliferated normally in culture and differentiated into infective metacyclic parasites and into intracellular and axenic amastigotes. In in vivo mouse infections, L. majorVTC4 knockout showed a delay in lesion formation but ultimately gave rise to strong pathology, although we were unable to restore virulence by complementation to confirm this phenotype. Knockdown of VTC4 did not alter the course of L. guyanensis infections in mice, suggesting that polyP was not required for infection, or that very low levels of it suffice for lesion development. At higher temperatures, Leishmania promastigotes highly consumed polyP, and both knockdown or deletion of VTC4 diminished parasite survival. Thus, although polyP was not essential in the life cycle of the parasite, our data suggests a role for polyP in increasing parasite survival at higher temperatures, a situation faced by the parasite when transmitted to humans.

A soluble inorganic pyrophosphatase from the cattle tick Rhipicephalus microplus capable of hydrolysing polyphosphates

Polyphosphates have been found in all cell types examined to date and play diverse roles depending on the cell type. In eukaryotic organisms, polyphosphates have been investigated mainly in mammalian cells, and only a few studies have addressed arthropods. Pyrophosphatases have been shown to regulate polyphosphate metabolism. However, these studies were restricted to trypanosomatids. Here we focus on the tick Rhipicephalus microplus, a haematophagous ectoparasite that is highly harmful to cattle. We produced a recombinant R. microplus pyrophosphatase (rRmPPase) with the aim of investigating its kinetic parameters using polyphosphates as substrate. Molecular docking assays of RmPPase with polyphosphates were also carried out. The kinetic and Hill coefficient parameters indicated that rRmPPase has a greater affinity, higher catalytic efficiency and increased cooperativity for sodium phosphate glass type 15 (polyP₁₅ ) than for sodium tripolyphosphate (polyP₃ ). Through molecular docking, we found that polyP₃ binds close to the Mg²⁺ atoms in the catalytic region of the protein, participating in their coordination network, whereas polyP₁₅ interactions involve negatively charged phosphate groups and basic amino acid residues, such as Lys56, Arg58 and Lys193; polyP₁₅ has a more favourable theoretical binding affinity than polyP₃ , thus supporting the kinetic data. This study shows, for the first time in arthropods, a pyrophosphatase with polyphosphatase activity, suggesting its participation in polyphosphate metabolism.

A novel glucosamine-linked fluorescent chemosensor for the detection of pyrophosphate in an aqueous medium and live cells

A glucosamine-linked Cu²⁺ ensemble has been successfully developed for detection of pyrophosphate (PPi) in aqueous medium and in live MD-AMB-231 cells.

Identification of a novel PYP-1 gene in Sarcoptes scabiei and its potential as a serodiagnostic candidate by indirect-ELISA

Scabies is a parasitic disease caused by the ectoparasite Sarcoptes scabiei, affecting different mammalian species, including rabbits, worldwide. In the present study, we cloned and expressed a novel inorganic pyrophosphatase, Ssc-PYP-1, from S. scabiei var. cuniculi. Immunofluorescence staining showed that native Ssc-PYP-1 was localized in the tegument around the mouthparts and the entire legs, as well as in the cuticle of the mites. Interestingly, obvious staining was also observed on the fecal pellets of mites and in the integument of the mites. Based on its good immunoreactivity, an indirect enzyme-linked immunosorbent assay (ELISA) using recombinant Ssc-PYP-1 (rSsc-PYP-1) as the capture antigen was developed to diagnose sarcoptic mange in naturally infected rabbits; the assay had a sensitivity of 92·0% and specificity of 93·6%. Finally, using the rSsc-PYP-1-ELISA, the Ssc-PYP-1 antibody from 10 experimentally infected rabbits could be detected from 1 week post-infection. This is the first report of S. scabiei inorganic pyrophosphatase and the protein could serve as a potential serodiagnostic candidate for sarcoptic mange in rabbits.

Inorganic pyrophosphatases of Family II-two decades after their discovery

Inorganic pyrophosphatases (PPases) convert pyrophosphate (PP_i ) to phosphate and are present in all cell types. Soluble PPases belong to three nonhomologous families, of which Family II is found in approximately a quarter of prokaryotic organisms, often pathogenic ones. Each subunit of dimeric canonical Family II PPases is formed by two domains connected by a flexible linker, with the active site located between the domains. These enzymes require both magnesium and a transition metal ion (manganese or cobalt) for maximal activity and are the most active (k_cat ≈ 10⁴ s^-1 ) among all PPase types. Catalysis by Family II PPases requires four metal ions per substrate molecule, three of which form a unique trimetal center that coordinates the nucleophilic water and converts it to a reactive hydroxide ion. A quarter of Family II PPases contain an autoinhibitory regulatory insert formed by two cystathionine β-synthase (CBS) domains and one DRTGG domain. Adenine nucleotide binding either activates or inhibits the CBS domain-containing PPases, thereby tuning their activity and, hence, PP_i levels, in response to changes in cell energy status (ATP/ADP ratio).

Structural and Biochemical Characterization of Apicomplexan Inorganic Pyrophosphatases

Inorganic pyrophosphatases (PPase) participate in energy cycling and they are essential for growth and survival of organisms. Here we report extensive structural and functional characterization of soluble PPases from the human parasites Plasmodium falciparum (PfPPase) and Toxoplasma gondii (TgPPase). Our results show that PfPPase is a cytosolic enzyme whose gene expression is upregulated during parasite asexual stages. Cambialistic PfPPase actively hydrolyzes linear short chain polyphosphates like PP_i, polyP₃ and ATP in the presence of Zn²⁺. A remarkable new feature of PfPPase is the low complexity asparagine-rich N-terminal region that mediates its dimerization. Deletion of N-region has an unexpected and substantial effect on the stability of PfPPase domain, resulting in aggregation and significant loss of enzyme activity. Significantly, the crystal structures of PfPPase and TgPPase reveal unusual and unprecedented dimeric organizations and provide new fundamental insights into the variety of oligomeric assemblies possible in eukaryotic inorganic PPases.

Role of leishmanial acidocalcisomal pyrophosphatase in the cAMP homeostasis in phagolysosome conditions required for intra-macrophage survival

Exposure of Leishmania donovani to macrophage phagolysosome conditions (PC) (37°C and pH 5.5) led to increased intracellular cAMP and cAMP-mediated responses, which help in intra-macrophage survival pre-requisite for infectivity. In the absence of typical orthologs for G-proteins and G-protein coupled receptors, we sought to study the precise mechanisms for positive modulation of cAMP production during exposure to PC. Amongst two promastigote-stage specific membrane bound receptor adenylate cyclases (LdRAC-A and LdRAC-B), LdRAC-A appeared to function as a major cAMP generator following PC exposure. Pyrophosphate (PPi), an energy storage compound as well as a by-product of cAMP biosynthesis by adenylate cyclise, was found to be decreased following PC exposure. This may be due to microtubule and microfilament-driven translocation of acidocalcisomes near plasma membrane vicinity with concomitant increase of acidocalcisome membrane pyrophosphatase (LdV-H⁺PPase) and acidocalcisomal soluble pyrophosphatase (LdVSP1). Episomal over-expression and conditional silencing demonstrated regulatory role of V-H⁺PPase on cAMP trigger and consequent induction of resistance to macrophage-derived pro-oxidants and parasite killing. Furthermore, immunofluorescence analysis revealed possible co-localization of LdV-H⁺PPase and LdRAC-A during PC exposure. Collectively, these results suggest that translocation of acidocalcisome in membrane vicinity functions as a trigger for LdRAC-A-driven cAMP generation through depletion of PPi pool by LdV-H⁺PPase.

Ppn2, a novel Zn2+-dependent polyphosphatase in the acidocalcisome-like yeast vacuole

Acidocalcisome-like organelles are found in all kingdoms of life. Many of their functions, such as the accumulation and storage of metal ions, nitrogen and phosphate, the activation of blood clotting and inflammation, depend on the controlled synthesis and turnover of polyphosphate (polyP), a polymer of inorganic phosphate linked by phosphoric anhydride bonds. The exploration of the role of acidocalcisomes in metabolism and physiology requires manipulation of polyP turnover, yet the complete set of proteins responsible for this turnover is unknown. Here, we identify a novel type of polyphosphatase operating in the acidocalcisome-like vacuoles of yeast, Ppn2. Ppn2 belongs to the PPP-superfamily of metallo-phosphatases, is activated by Zn2+ ions and exclusively shows endopolyphosphatase activity. It is sorted to vacuoles via the multivesicular body pathway. Together with Ppn1, Ppn2 constitutes a major fraction of polyphosphatase activity that is necessary to mobilize polyP stores, for example in response to phosphate scarcity. This finding opens the way to manipulating polyP metabolism more profoundly and deciphering its roles in phosphate and energy homeostasis, as well as in signaling.

Polyphosphate and acidocalcisomes

Inorganic polyphosphate (polyP) accumulates in acidocalcisomes, acidic calcium stores that have been found from bacteria to human cells. Proton pumps, such as the vacuolar proton pyrophosphatase (V-H(+)-PPase or VP1), the vacuolar proton ATPase (V-H(+)-ATPase) or both, maintain their acidity. A vacuolar transporter chaperone (VTC) complex is involved in the synthesis and translocation of polyP to these organelles in several eukaryotes, such as yeast, trypanosomatids, Apicomplexan and algae. Studies in trypanosomatids have revealed the role of polyP and acidocalcisomes in osmoregulation and calcium signalling.

Structures of Trypanosome Vacuolar Soluble Pyrophosphatases: Antiparasitic Drug Targets

Trypanosomatid parasites are the causative agents of many neglected tropical diseases, including the leishmaniases, Chagas disease, and human African trypanosomiasis. They exploit unusual vacuolar soluble pyrophosphatases (VSPs), absent in humans, for cell growth and virulence and, as such, are drug targets. Here, we report the crystal structures of VSP1s from Trypanosoma cruzi and T. brucei, together with that of the T. cruzi protein bound to a bisphosphonate inhibitor. Both VSP1s form a hybrid structure containing an (N-terminal) EF-hand domain fused to a (C-terminal) pyrophosphatase domain. The two domains are connected via an extended loop of about 17 residues. Crystallographic analysis and size exclusion chromatography indicate that the VSP1s form tetramers containing head-to-tail dimers. Phosphate and diphosphate ligands bind in the PPase substrate-binding pocket and interact with several conserved residues, and a bisphosphonate inhibitor (BPH-1260) binds to the same site. On the basis of Cytoscape and other bioinformatics analyses, it is apparent that similar folds will be found in most if not all trypanosomatid VSP1s, including those found in insects (Angomonas deanei, Strigomonas culicis), plant pathogens (Phytomonas spp.), and Leishmania spp. Overall, the results are of general interest since they open the way to structure-based drug design for many of the neglected tropical diseases.

Acidocalcisomes of eukaryotes

Acidocalcisomes are organelles rich in polyphosphate and cations and acidified by proton pumps. Although they have also been described in prokaryotes they have been better characterized in unicellular and multicellular eukaryotes. Eukaryotic acidocalcisomes belong to the group of lysosome-related organelles. They have a variety of functions, from the storage of cations and phosphorus to calcium signaling, autophagy, osmoregulation, blood coagulation, and inflammation. Acidocalcisomes of several unicellular eukaryotes possess a variety of transporters, channels and pumps implying a large energetic requirement for their maintenance and suggesting other important functions waiting to be discovered.

The origin and evolution of the acidocalcisome and its interactions with other organelles

Acidocalcisomes are acidic calcium stores that have been found from bacteria to human cells. They are rich in phosphorus compounds in the form of orthophosphate (P_i), pyrophosphate (PP_i), and polyphosphate (polyP) and their acidity is maintained by proton pumps such as the vacuolar proton pyrophosphatase (V-H⁺-PPase, or VP1), the vacuolar proton ATPase (V-H⁺-ATPase), or both. Recent studies in trypanosomatids and in other species have revealed their role in phosphate metabolism, and cation and water homeostasis, as suggested by the presence of novel pumps, transporters, and channels. An important role in autophagy has also been described. The study of the biogenesis of acidocalcisomes as well as of the interactions of these lysosome-related organelles with other organelles have uncovered important roles in calcium signaling and osmoregulation. Significantly, despite conservation of acidocalcisomes across all of cellular life, there is evidence for intimate integration of these organelles with eukaryotic cellular functions, and which are directly relevant to parasites.

Structural and Functional Highlights of Vacuolar Soluble Protein 1 from Pathogen Trypanosoma brucei brucei

Trypanosoma brucei (T. brucei) is responsible for the fatal human disease called African trypanosomiasis, or sleeping sickness. The causative parasite, Trypanosoma, encodes soluble versions of inorganic pyrophosphatases (PPase), also called vacuolar soluble proteins (VSPs), which are localized to its acidocalcisomes. The latter are acidic membrane-enclosed organelles rich in polyphosphate chains and divalent cations whose significance in these parasites remains unclear. We here report the crystal structure of T. brucei brucei acidocalcisomal PPases in a ternary complex with Mg(2+) and imidodiphosphate. The crystal structure reveals a novel structural architecture distinct from known class I PPases in its tetrameric oligomeric state in which a fused EF hand domain arranges around the catalytic PPase domain. This unprecedented assembly evident from TbbVSP1 crystal structure is further confirmed by SAXS and TEM data. SAXS data suggest structural flexibility in EF hand domains indicative of conformational plasticity within TbbVSP1.

CRISPR/Cas9-Induced Disruption of Paraflagellar Rod Protein 1 and 2 Genes in Trypanosoma cruzi Reveals Their Role in Flagellar Attachment

Trypanosoma cruzi is the etiologic agent of Chagas disease, and current methods for its genetic manipulation have been highly inefficient. We report here the use of the CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 (CRISPR-associated gene 9) system for disrupting genes in the parasite by three different strategies. The utility of the method was established by silencing genes encoding the GP72 protein, which is required for flagellar attachment, and paraflagellar rod proteins 1 and 2 (PFR1, PFR2), key components of the parasite flagellum. We used either vectors containing single guide RNA (sgRNA) and Cas9, separately or together, or one vector containing sgRNA and Cas9 plus donor DNA for homologous recombination to rapidly generate mutant cell lines in which the PFR1, PFR2, and GP72 genes have been disrupted. We demonstrate that genome editing of these endogenous genes in T. cruzi is successful without detectable toxicity of Cas9. Our results indicate that PFR1, PFR2, and GP72 contribute to flagellar attachment to the cell body and motility of the parasites. Therefore, CRISPR/Cas9 allows efficient gene disruption in an almost genetically intractable parasite and suggest that this method will improve the functional analyses of its genome.

Trypanosoma cruzi is the agent of Chagas disease, which affects millions of people worldwide. Vaccines to prevent this disease are not available, and drug treatments are not completely effective. The study of the biology of this parasite through genetic approaches will make possible the development of new preventive or treatment options. Previous attempts to use the CRISPR/Cas9 in T. cruzi found a detectable but low frequency of Cas9-facilitated homologous recombination and fluorescent marker swap between exogenous genes, while Cas9 was toxic to the cells. In this report, we describe new approaches that generate complete disruption of an endogenous gene without toxicity to the parasites and establish the relevance of several proteins for flagellar attachment and motility.

Proteomic analysis of acidocalcisomes of Trypanosoma brucei uncovers their role in phosphate metabolism, cation homeostasis, and calcium signaling

Trypanosomabrucei, the causative agent of African trypanosomiasis, is a unicellular parasite that possesses lysosome-related organelles known as acidocalcisomes. These organelles have been found from bacteria to human cells, and are characterized by their acidic nature and high calcium and polyphosphate (polyP) content. Our proteomic analysis of acidocalcisomes of T. brucei procyclic stages, together with in situ epitope-tagging and immunofluorescence assays with specific antibodies against selected proteins, established the presence of 2 H⁺ pumps, a vacuolar H⁺-ATPase and a vacuolar H⁺-pyrophosphatase, that acidify the organelles as well as of a number of transporters and channels involved in phosphate metabolism, cation uptake and calcium signaling. Together with recent work in other organisms, these results provide direct evidence that acidocalcisomes are especially adapted to accumulate polyP bound to cations and for calcium signaling.

A soluble pyrophosphatase is essential to oogenesis and is required for polyphosphate metabolism in the red flour beetle (Tribolium castaneum)

Polyphosphates have been found in all cell types examined to date and play diverse roles depending on the cell type. In eukaryotic organisms, polyphosphates have been mainly investigated in mammalian cells with few studies on insects. Some studies have demonstrated that a pyrophosphatase regulates polyphosphate metabolism, and most of them were performed on trypanosomatids. Here, we investigated the effects of sPPase gene knocked down in oogenesis and polyphosphate metabolism in the red flour beetle (Tribolium castaneum) A single sPPase gene was identified in insect genome and is maternally provided at the mRNA level and not restricted to any embryonic or extraembryonic region during embryogenesis. After injection of Tc-sPPase dsRNA, female survival was reduced to 15% of the control (dsNeo RNA), and egg laying was completely impaired. The morphological analysis by nuclear DAPI staining of the ovarioles in Tc-sPPase dsRNA-injected females showed that the ovariole number is diminished, degenerated oocytes can be observed, and germarium is reduced. The polyphosphate level was increased in cytoplasmic and nuclear fractions in Tc-sPPase RNAi; Concomitantly, the exopolyphosphatase activity decreased in both fractions. Altogether, these data suggest a role for sPPase in the regulation on polyphosphate metabolism in insects and provide evidence that Tc-sPPase is essential to oogenesis.

Role of β-hydroxybutyrate, its polymer poly-β-hydroxybutyrate and inorganic polyphosphate in mammalian health and disease

We provide a comprehensive review of the role of β-hydroxybutyrate (β-OHB), its linear polymer poly-β-hydroxybutyrate (PHB), and inorganic polyphosphate (polyP) in mammalian health and disease. β-OHB is a metabolic intermediate that constitutes 70% of ketone bodies produced during ketosis. Although ketosis has been generally considered as an unfavorable pathological state (e.g., diabetic ketoacidosis in type-1 diabetes mellitus), it has been suggested that induction of mild hyperketonemia may have certain therapeutic benefits. β-OHB is synthesized in the liver from acetyl-CoA by β-OHB dehydrogenase and can be used as alternative energy source. Elevated levels of PHB are associated with pathological states. In humans, short-chain, complexed PHB (cPHB) is found in a wide variety of tissues and in atherosclerotic plaques. Plasma cPHB concentrations correlate strongly with atherogenic lipid profiles, and PHB tissue levels are elevated in type-1 diabetic animals. However, little is known about mechanisms of PHB action especially in the heart. In contrast to β-OHB, PHB is a water-insoluble, amphiphilic polymer that has high intrinsic viscosity and salt-solvating properties. cPHB can form non-specific ion channels in planar lipid bilayers and liposomes. PHB can form complexes with polyP and Ca(2+) which increases membrane permeability. The biological roles played by polyP, a ubiquitous phosphate polymer with ATP-like bonds, have been most extensively studied in prokaryotes, however polyP has recently been linked to a variety of functions in mammalian cells, including blood coagulation, regulation of enzyme activity in cancer cells, cell proliferation, apoptosis and mitochondrial ion transport and energy metabolism. Recent evidence suggests that polyP is a potent activator of the mitochondrial permeability transition pore in cardiomyocytes and may represent a hitherto unrecognized key structural and functional component of the mitochondrial membrane system.