Characterization of the plasma-membrane calcium pump from Trypanosoma cruzi.
Ontology highlight
ABSTRACT:
SUBMITTER: Benaim G
PROVIDER: S-EPMC1136516 | biostudies-other | 1995 Feb
REPOSITORIES: biostudies-other
Similar Datasets
Project description:The survival of a eukaryotic protozoan as an obligate parasite in the interior of a eukaryotic host cell implies its adaptation to an environment with a very different ionic composition from that of its extracellular habitat. This is particularly important in the case of Ca2+, the intracellular concentration of which is 3 orders of magnitude lower than the extracellular value. Ca2+ entry across the plasma membrane is a widely recognized mechanism for Ca2+ signaling, needed for a number of intracellular processes, and obviously, it would be restricted in the case of intracellular parasites. Here we show that Trypanosoma cruzi amastigotes possess a higher Ca2+ content than the extracellular stages of the parasite. This correlates with the higher expression of a calcium pump, the gene for which was cloned and sequenced. The deduced protein product (Tca1) of this gene has a calculated molecular mass of 121,141 Da and exhibits 34 to 38% identity with vacuolar Ca2+-ATPases of Saccharomyces cerevisiae and Dictyostelium discoideum, respectively. The tca1 gene suppresses the Ca2+ hypersensitivity of a mutant of S. cerevisiae that has a defect in vacuolar Ca2+ accumulation. Indirect immunofluorescence and immunoelectron microscopy analysis indicate that Tca1 colocalizes with the vacuolar H+-ATPase to the plasma membrane and to intracellular vacuoles of T. cruzi. These vacuoles were shown to have the same size and distribution as the calcium-containing vacuoles identified by the potassium pyroantimoniate-osmium technique and as the electron-dense vacuoles observed in whole unfixed parasites by transmission electron microscopy and identified in a previous work (D. A. Scott, R. Docampo, J. A. Dvorak, S. Shi, and R. D. Leapman, J. Biol. Chem. 272:28020-28029, 1997) as being acidic and possessing a high calcium content (i.e., acidocalcisomes). Together, these results suggest that acidocalcisomes are distinct from other previously recognized organelles present in these parasites and underscore the ability of intracellular parasites to adapt to the hostile environment of their hosts.
| S-EPMC121484 | biostudies-literature
Project description:During the aggregation and differentiation of amoebae of Dictyostelium discoideum, changes in free cytosolic Ca2+ appear to regulate a number of physiological processes. To understand the mechanisms regulating free intracellular Ca2+ in this organism, we have isolated and characterized an ATP/Mg2+-dependent, high-affinity Ca2+ pump. When homogenates of 2 h starved cells were fractionated on Percoll/KCl gradients, one peak of high-affinity Ca2+-pumping activity was detected. This activity was resolved from enzyme markers of the mitochondrion and the rough endoplasmic reticulum but it cosedimented with the plasma membrane marker, alkaline phosphatase. Further studies suggested that the pump was associated with 'inside-out' plasma membrane vesicles. Like plasma membrane Ca2+-transport ATPases from other systems, this isolated Ca2+ pump: (1) was Mg2+-dependent, (2) displayed a high specificity for ATP as an energy source, (3) exhibited a high affinity for free Ca2+ with a Km of 0.3 microM, and (4) was very sensitive to inhibition by vanadate (IC50 2 microM) but was unaffected by mitochondrial inhibitors, ouabain and Ca2+-channel blockers. Unlike plasma membrane Ca2+ pumps from most other systems, this enzyme appeared not to be regulated by calmodulin. During development, non-mitochondrial, vanadate-sensitive, high-affinity Ca2+-pumping activity in crude lysates remained relatively constant for at least 15 h. These observations suggest that this plasma membrane Ca2+ pump probably functions in Dictyostelium to maintain Ca2+ homeostasis by extruding free cytosolic Ca2+ from the cells.
| S-EPMC1148688 | biostudies-other
Project description:BackgroundTrypomastigotes of Trypanosoma cruzi are able to invade several types of non-phagocytic cells through a lysosomal dependent mechanism. It has been shown that, during invasion, parasites trigger host cell lysosome exocytosis, which initially occurs at the parasite-host contact site. Acid sphingomyelinase released from lysosomes then induces endocytosis and parasite internalization. Lysosomes continue to fuse with the newly formed parasitophorous vacuole until the parasite is completely enclosed by lysosomal membrane, a process indispensable for a stable infection. Previous work has shown that host membrane cholesterol is also important for the T. cruzi invasion process in both professional (macrophages) and non-professional (epithelial) phagocytic cells. However, the mechanism by which cholesterol-enriched microdomains participate in this process has remained unclear.Methodology/principal findingIn the present work we show that cardiomyocytes treated with MβCD, a drug able to sequester cholesterol from cell membranes, leads to a 50% reduction in invasion by T. cruzi trypomastigotes, as well as a decrease in the number of recently internalized parasites co-localizing with lysosomal markers. Cholesterol depletion from host membranes was accompanied by a decrease in the labeling of host membrane lipid rafts, as well as excessive lysosome exocytic events during the earlier stages of treatment. Precocious lysosomal exocytosis in MβCD treated cells led to a change in lysosomal distribution, with a reduction in the number of these organelles at the cell periphery, and probably compromises the intracellular pool of lysosomes necessary for T. cruzi invasion.Conclusion/significanceBased on these results, we propose that cholesterol depletion leads to unregulated exocytic events, reducing lysosome availability at the cell cortex and consequently compromise T. cruzi entry into host cells. The results also suggest that two different pools of lysosomes are available in the cell and that cholesterol depletion may modulate the fusion of pre-docked lysosomes at the cell cortex.
| S-EPMC3313932 | biostudies-literature
Project description:The aim of this work was to study the plasma membrane calcium pump (PMCA) reaction cycle by characterizing conformational changes associated with calcium, ATP, and vanadate binding to purified PMCA. This was accomplished by studying the exposure of PMCA to surrounding phospholipids by measuring the incorporation of the photoactivatable phosphatidylcholine analog 1-O-hexadecanoyl-2-O-[9-[[[2-[(125)I]iodo-4-(trifluoromethyl-3H-diazirin-3-yl)benzyl]oxy]carbonyl]nonanoyl]-sn-glycero-3-phosphocholine to the protein. ATP could bind to the different vanadate-bound states of the enzyme either in the presence or in the absence of Ca(2+) with high apparent affinity. Conformational movements of the ATP binding domain were determined using the fluorescent analog 2'(3')-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate. To assess the conformational behavior of the Ca(2+) binding domain, we also studied the occlusion of Ca(2+), both in the presence and in the absence of ATP and with or without vanadate. Results show the existence of occluded species in the presence of vanadate and/or ATP. This allowed the development of a model that describes the transport of Ca(2+) and its relation with ATP hydrolysis. This is the first approach that uses a conformational study to describe the PMCA P-type ATPase reaction cycle, adding important features to the classical E1-E2 model devised using kinetics methodology only.
| S-EPMC3829416 | biostudies-literature
Project description:Alpha-synuclein (aSN) is a membrane-associated and intrinsically disordered protein, well-known for pathological aggregation in neurodegeneration. However, the physiological function of aSN is disputed. Pull-down experiments have pointed to plasma membrane Ca2+-ATPase (PMCA) as a potential interaction partner. From proximity ligation assays we find that aSN and PMCA colocalize at neuronal synapses, and we show that calcium expulsion is activated by aSN and PMCA. We further show that soluble, monomeric aSN activates PMCA at par with calmodulin, but independent of the autoinhibitory domain of PMCA, and highly dependent on acidic phospholipids and membrane-anchoring properties of aSN. On PMCA, the key site is mapped to the acidic lipid-binding site, located within a disordered PMCA-specific loop connecting the cytosolic A domain and transmembrane segment 3. Our studies point towards a novel physiological role of monomeric aSN as a stimulator of calcium clearance in neurons through activation of PMCA
| S-SCDT-10_15252-EMBJ_2022111122 | biostudies-other
Project description:The Homer family of scaffold proteins couples NMDA receptors to metabotropic glutamate receptors and links extracellular signals to calcium release from intracellular stores. Ania-3 is a member of the Homer family and is rapidly inducible in brain in response to diverse stimuli. Here, we report the identification of the plasma membrane Ca2+ ATPase (PMCA) as a novel Ania-3/Homer-associated protein. Ania-3/Homer interacts with the b-splice forms of all PMCAs (PMCA1b, 2b, 3b, and 4b) via their PDZ domain-binding COOH-terminal tail. Ectopically expressed Ania-3 colocalized with the PMCA at the plasma membrane of polarized MDCK epithelial cells, and endogenous Ania-3/Homer and PMCA2 are co-expressed in the soma and dendrites of primary rat hippocampal neurons. The interaction between Ania-3/Homer and PMCAs may represent a novel mechanism by which local calcium signaling and hence synaptic function can be modulated in neurons.
| S-EPMC3873836 | biostudies-literature
Project description:Plasma membrane proton pump maintains proton electrochemical gradient and provides energy to secondary transporters. Arabidopsis mutant plants with reduced proton pump activity grow normal under ideal growth conditions; however their growth are reduced compared with wildtype plants when placed under the conditions that stress on protonmotive force (high external pH or high external potassium).
2015-04-01 | GSE34202 | GEO
Project description:Plasma membrane proton pump maintains proton electrochemical gradient and provides energy to secondary transporters. Arabidopsis mutant plants with reduced proton pump activity grow normal under ideal growth conditions; however their growth are reduced compared with wildtype plants when placed under the conditions that stress on protonmotive force (high external pH or high external potassium). Seedlings of wildtype, aha1, and aha2 mutant plants were grown under ideal growth condition. Total RNA from those seedlings were subjected to transcriptome analyses using Affymetrix Gene Chip.
2015-04-01 | E-GEOD-34202 | biostudies-arrayexpress
Project description:Trypanosoma cruzi develops in environments where nutrient availability, osmolarity, ionic concentrations, and pH undergo significant changes. The ability to adapt and respond to such conditions determines the survival and successful transmission of T. cruzi. Ion channels play fundamental roles in controlling physiological parameters that ensure cell homeostasis by rapidly triggering compensatory mechanisms. Combining molecular, cellular and electrophysiological approaches we have identified and characterized the expression and function of a novel calcium-activated potassium channel (TcCAKC). This channel resides in the plasma membrane of all 3 life stages of T. cruzi and shares structural features with other potassium channels. We expressed TcCAKC in Xenopus laevis oocytes and established its biophysical properties by two-electrode voltage clamp. Oocytes expressing TcCAKC showed a significant increase in inward currents after addition of calcium ionophore ionomycin or thapsigargin. These responses were abolished by EGTA suggesting that TcCAKC activation is dependent of extracellular calcium. This activation causes an increase in current and a negative shift in reversal potential that is blocked by barium. As predicted, a single point mutation in the selectivity filter (Y313A) completely abolished the activity of the channels, confirming its potassium selective nature. We have generated knockout parasites deleting one or both alleles of TcCAKC. These parasite strains showed impaired growth, decreased production of trypomastigotes and slower intracellular replication, pointing to an important role of TcCAKC in regulating infectivity. To understand the cellular mechanisms underlying these phenotypic defects, we used fluorescent probes to evaluate intracellular membrane potential, pH, and intracellular calcium. Epimastigotes lacking the channel had significantly lower cytosolic calcium, hyperpolarization, changes in intracellular pH, and increased rate of proton extrusion. These results are in agreement with previous reports indicating that, in trypanosomatids, membrane potential and intracellular pH maintenance are linked. Our work shows TcCAKC is a novel potassium channel that contributes to homeostatic regulation of important physiological processes in T. cruzi and provides new avenues to explore the potential of ion channels as targets for drug development against protozoan parasites.
| S-EPMC6974456 | biostudies-literature
Project description:The flagellar calcium-binding protein (FCaBP) of the protozoan Trypanosoma cruzi is targeted to the flagellar membrane where it regulates flagellar function and assembly. As a first step toward understanding the Ca(2+)-induced conformational changes important for membrane-targeting, we report here the x-ray crystal structure of FCaBP in the Ca(2+)-free state determined at 2.2A resolution. The first 17 residues from the N terminus appear unstructured and solvent-exposed. Residues implicated in membrane targeting (Lys-19, Lys-22, and Lys-25) are flanked by an exposed N-terminal helix (residues 26-37), forming a patch of positive charge on the protein surface that may interact electrostatically with flagellar membrane targets. The four EF-hands in FCaBP each adopt a "closed conformation" similar to that seen in Ca(2+)-free calmodulin. The overall fold of FCaBP is closest to that of grancalcin and other members of the penta EF-hand superfamily. Unlike the dimeric penta EF-hand proteins, FCaBP lacks a fifth EF-hand and is monomeric. The unstructured N-terminal region of FCaBP suggests that its covalently attached myristoyl group at the N terminus may be solvent-exposed, in contrast to the highly sequestered myristoyl group seen in recoverin and GCAP1. NMR analysis demonstrates that the myristoyl group attached to FCaBP is indeed solvent-exposed in both the Ca(2+)-free and Ca(2+)-bound states, and myristoylation has no effect on protein structure and folding stability. We propose that exposed acyl groups at the N terminus may anchor FCaBP to the flagellar membrane and that Ca(2+)-induced conformational changes may control its binding to membrane-bound protein targets.
| S-EPMC2516990 | biostudies-literature