SummaryIn animals, inositol 1,4,5-trisphosphate receptors (IP3Rs) are ion channels that play a pivotal role in many biological processes by mediating Ca 2+ release from the endoplasmic reticulum. Here, we report the identification and characterization of a novel IP3R in the parasitic protist, Trypanosoma cruzi, the pathogen responsible for Chagas disease. DT40 cells lacking endogenous IP3R genes expressing T. cruzi IP3R (TcIP3R) exhibited IP3-mediated Ca 2+ release from the ER, and demonstrated receptor binding to IP3. TcIP3R was expressed throughout the parasite life cycle but the expression level was much lower in bloodstream trypomastigotes than in intracellular amastigotes or epimastigotes. Disruption of two of the three TcIP 3R gene loci led to the death of the parasite, suggesting that IP3R is essential for T. cruzi. Parasites expressing reduced or increased levels of TcIP3R displayed defects in growth, transformation and infectivity, indicating that TcIP3R is an important regulator of the parasite's life cycle. Furthermore, mice infected with T. cruzi expressing reduced levels of TcIP3R exhibited a reduction of disease symptoms, indicating that TcIP3R is an important virulence factor. Combined with the fact that the primary structure of TcIP3R has low similarity to that of mammalian IP3Rs, TcIP3R is a promising drug target for Chagas disease.

Mitochondrial respiratory enzymes play a central role in energy production in aerobic organisms. They differentiated from the ␣-proteobacteria-derived ancestors by adding noncatalytic subunits. An exception is Complex II (succinate: ubiquinone reductase), which is composed of four ␣-proteobacteria-derived catalytic subunits (SDH1-SDH4). Complex II often plays a pivotal role in adaptation of parasites in host organisms and would be a potential target for new drugs. We purified Complex II from the parasitic protist Trypanosoma cruzi and obtained the unexpected result that it consists of six hydrophilic (SDH1, SDH2 N , SDH2 C , and SDH5-SDH7) and six hydrophobic (SDH3, SDH4, and SDH8 -SDH11) nucleus-encoded subunits. Orthologous genes for each subunit were identified in Trypanosoma brucei and Leishmania major. Notably, the iron-sulfur subunit was heterodimeric; SDH2 N and SDH2 C contain the plant-type ferredoxin domain in the N-terminal half and the bacterial ferredoxin domain in the C-terminal half, respectively. Catalytic subunits (SDH1, SDH2 N plus SDH2 C , SDH3, and SDH4) contain all key residues for binding of dicarboxylates and quinones, but the enzyme showed the lower affinity for both substrates and inhibitors than mammalian enzymes. In addition, the enzyme binds protoheme IX, but SDH3 lacks a ligand histidine. These unusual features are unique in the Trypanosomatida and make their Complex II a target for new chemotherapeutic agents.The parasitic protist Trypanosoma cruzi is the etiological agent of Chagas disease, a public health threat in Central and South America. These parasites are normally transmitted by reduviid bugs via the vector feces after a bug bite and also via transfusion of infected blood. About 16 -18 million people are infected, and 100 million are at risk, but there are no definitive chemotherapeutic treatments available (1). Despite having potential pathways for oxidative phosphorylation (2), all trypanosomatids (Trypanosoma and Leishmania species) analyzed so far are characterized by incomplete oxidation of glucose with secretion of end products, such as succinate, alanine, ethanol, acetate, pyruvate, and glycerol (3, 4) (Fig. 1). Major routes for formation of succinate in Trypanosoma brucei are via NADH-dependent fumarate reductase in glycosomes and mitochondria (5, 6). In trypanosomatid mitochondria, the Krebs cycle is inefficient, and pyruvate is principally converted to acetate via acetate:succinate CoA transferase (7). A part of the Krebs cycle operates the utilization of histidine in the insect stage of T. cruzi (8).Mitochondrial Complex II (succinate:quinone reductase (SQR) 5 and succinate dehydrogenase (SDH)) serves as a membrane-bound Krebs cycle enzyme and often plays a pivotal role in adaptation of parasites to environments in their host (9, 10). In general, Complex II consists of four subunits (11). A flavoprotein subunit (SDH1, Fp) and an iron-sulfur subunit (SDH2, Ip) form a soluble heterodimer, which then binds to a membrane anchor heterodimer, SDH3 (CybL) and SDH4 (CybS)....

The remodelling of organelle function is increasingly appreciated as a central driver of eukaryotic biodiversity and evolution. Kinetoplastids including Trypanosoma and Leishmania have evolved specialized peroxisomes, called glycosomes. Glycosomes uniquely contain a glycolytic pathway as well as other enzymes, which underpin the physiological flexibility of these major human pathogens. The sister group of kinetoplastids are the diplonemids, which are among the most abundant eukaryotes in marine plankton. Here we demonstrate the compartmentalization of gluconeogenesis, or glycolysis in reverse, in the peroxisomes of the free-living marine diplonemid, Diplonema papillatum. Our results suggest that peroxisome modification was already under way in the common ancestor of kinetoplastids and diplonemids, and raise the possibility that the central importance of gluconeogenesis to carbon metabolism in the heterotrophic free-living ancestor may have been an important selective driver. Our data indicate that peroxisome modification is not confined to the kinetoplastid lineage, but has also been a factor in the success of their free-living euglenozoan relatives.

Salt tolerance is an agronomically important trait that affects plant species around the globe. The Salt Overly Sensitive 1 (SOS1) gene encodes a plasma membrane Na+/H+ antiporter that plays an important role in germination and growth of plants in saline environments. Quinoa (Chenopodium quinoa Willd.) is a halophytic, allotetraploid grain crop of the family Amaranthaceae with impressive nutritional content and an increasing worldwide market. Many quinoa varieties have considerable salt tolerance, and research suggests quinoa may utilize novel mechanisms to confer salt tolerance. Here we report the cloning and characterization of two homoeologous SOS1 loci (cqSOS1A and cqSOS1B) from C. quinoa, including full-length cDNA sequences, genomic sequences, relative expression levels, fluorescent in situ hybridization (FISH) analysis, and a phylogenetic analysis of SOS1 genes from 13 plant taxa. The cqSOS1A and cqSOS1B genes each span 23 exons spread over 3477 bp and 3486 bp of coding sequence, respectively. These sequences share a high level of similarity with SOS1 homologs of other species and contain two conserved domains, a Nhap cation-antiporter domain and a cyclic-nucleotide binding domain. Genomic sequence analysis of two BAC clones (98 357 bp and 132 770 bp) containing the homoeologous SOS1 genes suggests possible conservation of synteny across the C. quinoa sub-genomes. This report represents the first molecular characterization of salt-tolerance genes in a halophytic species in the Amaranthaceae as well as the first comparative analysis of coding and non-coding DNA sequences of the two homoeologous genomes of C. quinoa.