ATP Hydrolase Research Articles

ATP Hydrolases Superfamily Protein 1 (ASP1) Maintains Root Stem Cell Niche Identity through Regulating Reactive Oxygen Species Signaling in Arabidopsis.

The maintenance of the root stem cell niche identity in Arabidopsis relies on the delicate balance of reactive oxygen species (ROS) levels in root tips; however, the intricate molecular mechanisms governing ROS homeostasis within the root stem cell niche remain unclear. In this study, we unveil the role of ATP hydrolase superfamily protein 1 (ASP1) in orchestrating root stem cell niche maintenance through its interaction with the redox regulator cystathionine β-synthase domain-containing protein 3 (CBSX3). ASP1 is exclusively expressed in the quiescent center (QC) cells and governs the integrity of the root stem cell niche. Loss of ASP1 function leads to enhanced QC cell division and distal stem cell differentiation, attributable to reduced ROS levels and diminished expression of SCARECROW and SHORT ROOT in root tips. Our findings illuminate the pivotal role of ASP1 in regulating ROS signaling to maintain root stem cell niche homeostasis, achieved through direct interaction with CBSX3.

Kinetic regularities of thiacalix[4]arene C-1087 inhibitory effect on the activity of Mg(2+)-dependent Ca(2+)-transporting ATP hydrolase in the plasma membrane of smooth muscle cells

The experiments with the suspension of plasma membranes of myometrium cells, treated with 0.1% digitonin solution, were used to study kinetic regularities of the inhibitory effect of tetra-N-phenylsulfonyl trifluoroacetamidine-thiacalixarene (С-1087) on the activity of Са2+,Mg2+-ATPase. The studies demonstrated the impact of C-1087 on the cumulative effect and the maximal velocity of ATP hydrolysis. No effect of С-1087 on the affinity between Са2+,Mg2+-ATPase, and АТР, affinity and cumulative effect of Ca ions and activation coefficient for Mg ions was revealed. A considerable decrease in the maximal velocity of ATP hydrolysis evidenced a complete non-competitive mechanism of inhibiting Са2+,Mg2+-АТРase activity with thiacalix[4]arene С-1087. Computer simulation demonstrated that thiacalix[4]arene С-1087 inhibiting effect on Са2+,Mg2+-ATPase may be conditioned by the cumulative effect of four spatially oriented N-sulfonylamidine groups on the upper rim of its macrocyclic platform.

Elucidating the mechanisms underlying astrocyte-microglia crosstalk in hippocampal neuroinflammation induced by acute diquat exposure.

The transition from paraquat (PQ) to diquat (DQ), both organic dication herbicides, in China has led to significant increases in the number of acute DQ poisoning cases. Case studies have shown that acute DQ poisoning resulted in injury to the central nervous system (CNS), but the mechanism underlying the injury remains to be explored. The present study aimed to investigate how DQ influenced purinergic signaling between astrocytes and microglia and whether extracellular ATP (eATP) was involved in promoting neuroinflammation induced by acute DQ toxicity through the activation of the P2X4/NLRP3 signaling pathway. We constructed a rat model of acute DQ toxicity to observe the pathological changes in hippocampal tissues after DQ exposure and measure the expression levels of IL-1β and TNF-α in the hippocampal tissue. We also established an in vitro co-culture model of C6 astrocytes and BV-2 microglia using transwell chambers, measured the amount of eATP secreted into C6 astrocytes after DQ treatment, and assessed the inflammatory response and changes in the P2X4/NLRP3 signaling pathway in BV-2 microglia. The results showed that the neurons in the hippocampal tissue of rats exhibited loose arrangement, nuclear consolidation, and necrosis after DQ exposure, and IL-1β and TNF-α levels were signification higher in the hippocampal tissue after DQ exposure. DQ exposure to the co-cultured cells induced an increase in ATP secretion from C6 astrocytes as well as a significant increase of P2X4, NLRP3, IL-1β, and IL-18 expression in BV-2 microglia. In contrast, pretreatment of C6 astrocytes with apyrase (an ATP hydrolase) resulted in a significant decrease of P2X4, NLRP3, IL-1β, and IL-18 expression in BV-2 microglia. Furthermore, inhibition of P2X4 expression in BV-2 microglia by transfection with si-P2X4 effectively reversed the increase of NLRP3, IL-1β, and IL-18 in BV-2 microglia induced by DQ when co-cultured with C6 astrocytes. These results indicate that astrocytes can activate the P2X4/NLRP3 signaling pathway in microglia through the DQ-induced extracellular release of ATP to promote neuroinflammation in rat hippocampal tissue.

Interaction between membrane curvature sensitive factors SpoVM and SpoIVA in Bicelle condition

SpoVM and SpoIVA are essential proteins for coat assembly in Bacillus subtilis. SpoVM is a membrane curvature sensor, specifically localized on the forespore membrane. SpoIVA is an ATP hydrolase that self-assembles by hydrolyzing ATP. In this work, SpoVM and its mutant SpoVMP9A were obtained by cyanogen bromide cleavage and reconstituted into bicelles. The purification of SpoIVA was achieved through a rigorous process involving Ni-NTA chromatography column and size exclusion chromatography. This study utilized Biacore to obtain a direct determination of the kinetic parameters of interaction between SpoVM (SpoVMP9A) and SpoIVA in Bicelle conditions.

Discovery and in vivo evaluation of novel inhibitors of the hydrolytic activity of mitochondrial F1Fo ATP synthase to alleviate myocardial ischemia reperfusion injury

Abstract Background F1Fo ATP-synthase is the mitochondrial complex responsible for ATP production. During myocardial ischemia, ATP synthase reverses its activity to hydrolyze ATP leading to energetic deficit and cardiac injury. We have previously discovered via in-silico virtual screening selective hydrolase inhibitors with pyrazole-pyridine scaffold and verified their inhibitory effect on hydrolysis on isolated murine mitochondria. Purpose In the present work we aimed to 1) synthesize novel hydrolase inhibitors, 2) select the best candidates to evaluate their effect against myocardial ischemia (I) reperfusion (R) injury in vivo and 3) investigate the underlying molecular mechanisms of cardioprotection. Methods The inhibitory effect on ATP hydrolysis for all compounds was evaluated on isolated murine heart mitochondria and at a cellular level on H9C2 cells in the presence of rotenone where their ability to maintain membrane potential was monitored. The previously described ATP hydrolase inhibitor BTB06584 (BTB) was used in vitro and in vivo as a reference and three novel compounds were selected for in vivo evaluation namely 1117, 1119 and STK-71. In the first cohort, C57Bl6 mice were randomized into 5 groups that received intravenously: 1) vehicle, 2) 1117, 3)1119, 4) STK-71 and 5) BTB. The administration was performed 10 min prior to 30 min of I and 2 hours of R and infarct size (IS) was determined. The dose of each compound was based on the effective concentration needed at a cellular level to inhibit the ATP hydrolysis. In a second cohort of mice, the best candidate and vehicle were given 10 min after the induction of I and IS was measured to test the intervention in a more translational setting. Finally, in the third cohort, the cardioprotective mechanism was investigated at the 10th min of R. Results We discovered three candidates that inhibit the ATP hydrolytic activity with comparable IC50 values to BTB. These three compounds inhibited ATP hydrolysis on the H9C2 cells at 50μΜ while BTB was inactive at the same concentration. In vivo, the three novel inhibitors reduced IS compared to the control group with STK-71 having the most remarkable cardioprotective effect while BTB did not result in attenuation of IS. STK-71 when given after the induction of I, also reduced IS indicating that its cardioprotective effect is pertained in a translational protocol. Regarding the mechanism of cardioprotection, STK-71 increased T173 phosphorylation and activation of PKA which led to the downstream activation of phospholamban. STK-71 also led to the significant activation of the RISK pathway, increased the expression of the antiapoptotic protein Bcl-Xl and reduced apoptosis. Conclusion We discovered a novel pyrazolopyridine derivative that acts as an inhibitor of ATP hydrolysis and reduces myocardial IS in vivo. Its cardioprotective mechanism involves the activation of PKA signaling and alleviation of apoptosis.

Reversible binding of divalent cations to Ductin protein assemblies-A putative new regulatory mechanism of membrane traffic processes.

Ductins are a family of homologous and structurally similar membrane proteins with 2 or 4 trans-membrane alpha-helices. The active forms of the Ductins are membranous ring- or star-shaped oligomeric assemblies and they provide various pore, channel, gap-junction functions, assist in membrane fusion processes and also serve as the rotor c-ring domain of V-and F-ATPases. All functions of the Ductins have been reported to be sensitive to the presence of certain divalent metal cations (Me2+), most frequently Cu2+ or Ca2+ ions, for most of the better known members of the family, and the mechanism of this effect is not yet known. Given that we have earlier found a prominent Me2+ binding site in a well-characterised Ductin protein, we hypothesise that certain divalent cations can structurally modulate the various functions of Ductin assemblies via affecting their stability by reversible non-covalent binding to them. A fine control of the stability of the assembly ranging from separated monomers through a loosely/weakly to tightly/strongly assembled ring might render precise regulation of Ductin functions possible. The putative role of direct binding of Me2+ to the c-ring subunit of active ATP hydrolase in autophagy and the mechanism of Ca2+-dependent formation of the mitochondrial permeability transition pore are also discussed.

Prognostic effect of CD73 in pancreatic ductal adenocarcinoma for disease-free survival after radical surgery.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with a high potency of metastasis or recurrence after radical resection. Effective predictors for metastasis and recurrence postoperatively were dominant for the development of systemic adjuvant treatment regimens. The ATP hydrolase correlated gene CD73 was described as a promoter in tumor growth and immune escape of PDAC. However, there lacked research focused on the role of CD73 in PDAC metastasis. This study aimed to investigate the expression of CD73 in PDAC patients with different outcomes as well as the prognostic effect of CD73 for disease-free survival (DFS). The expression level of CD73 in cancerous samples from 301 PDAC patients was evaluated by immunohistochemistry (IHC) and translated into a histochemistry score (H-score) by the HALO analysis system. Then, the CD73 H-score was involved in multivariate Cox regression along with other clinicopathological characteristics to find independent prognostic factors for DFS. Finally, a nomogram was constructed based on those independent prognostic factors for DFS prediction. Higher CD73 expression was found in PDAC patients with tumor metastasis postoperatively. Meanwhile, higher CD73 expressions were also investigated in PDAC patients diagnosed with advanced N stage and T stage. Furthermore, CD73 H-score along with tumor margin status, CA19-9, 8th N stage, and adjuvant chemotherapy was indicated as independent prognostic factors for DFS in PDAC patients. The nomogram based on these factors predicted DFS in a good manner. CD73 was associated with PDAC metastasis and served as an effective prognostic factor for DFS in PDAC patients after radical surgery.

Whole Genome Resequencing Revealed the Effect of Helicase yqhH Gene on Regulating Bacillus thuringiensis LLP29 against Ultraviolet Radiation Stress.

Bacillus thuringiensis (Bt) is a widely used microbial pesticide. However, its duration of effectiveness is greatly shortened due to the irradiation of ultraviolet rays, which seriously hinders the application of Bt preparations. Therefore, it is of great importance to study the resistance mechanism of Bt to UV at the molecular level to improve the UV-resistance of Bt strains. In order to know the functional genes in the UV resistance, the genome of UV-induced mutant Bt LLP29-M19 was re-sequenced and compared with the original strain Bt LLP29. It was shown that there were 1318 SNPs, 31 InDels, and 206 SV between the mutant strain and the original strain Bt LLP29 after UV irradiation, which were then analyzed for gene annotation. Additionally, a mutated gene named yqhH, a member of helicase superfamily II, was detected as an important candidate. Then, yqhH was expressed and purified successfully. Through the result of the enzymatic activity in vitro, yqhH was found to have ATP hydrolase and helicase activities. In order to further verify its function, the yqhH gene was knocked out and complemented by homologous recombinant gene knockout technology. The survival rate of the knockout mutant strain Bt LLP29-ΔyqhH was significantly lower than that of the original strain Bt LLP29 and the back-complemented strain Bt LLP29-ΔyqhH-R after treated with UV. Meanwhile, the total helicase activity was not significantly different on whether Bt carried yqhH or not. All of these greatly enrich important molecular mechanisms of Bt when it is in UV stress.

Rotations of F-ATPase and V-ATPase analyzed by a torque approach

F-type ATP synthase (F-ATPase) and vacuolar ATP hydrolase (V-ATPase) are well-known biomolecular motors, which play significant catalytic roles in ATP synthesis and ATP hydrolysis reactions. Their rotational torques are important factors involved in their rotational behavior that can be measured experimentally but with considerable difficulty. To overcome this difficulty and thereby provide an in-depth understanding of their operation mechanism, we herein carry out simple and fast computer modelling to study the two proteins, using our torque approach that relies on interatomic forces and coordinates of unequilibrated configurations taken from brief molecular dynamics (MD) simulations. As predicted by the torque approach, F-ATPase is demonstrated to be a random rotor, but it prefers to rotate in clockwise direction (as seen from the membrane toward the protein) for ATP synthesis, owing to the predominantly negative angle-averaged torques. By contrast, V-ATPase tends to rotate only in counterclockwise direction for ATP hydrolysis, due to the almost uniform averaged positive torques generated by the unidirectional rotation near the three catalytic sites. The rotational behaviors of both proteins are also affected by the surrounding solvent which can promote or hinder the internal rotation. By combining the torque approach with classic force-field MD simulations, the torques of two biomolecular motors can be calculated economically, and are found to agree with previous experiments and theoretical calculations. This work demonstrates that our torque approach can be extended to the field of biology and can help gain a deeper insight into the mechanistic rotation of biomolecular motors with modest computation time. Communicated by Ramaswamy H. Sarma

Cultivar-, stress duration- and leaf age-specific hub genes and co-expression networks responding to waterlogging in barley

Mature leaf degradation for supporting the younger leaf growth is a survival strategy for plants under waterlogging stress, but its molecular mechanism is rarely known. In this study, two barley cultivars Laurikka (B1) and Evergreen (B2), differing in waterlogging tolerance, were subjected to 6- or 10- day waterlogging stress during tillering stage. B1 was found more sensitive to waterlogging stress than B2, showing a more rapid leaf chlorophyll loss, but the elongation rate of the youngest leaf had little difference between the two cultivars. The youngest and mature leaves were sampled for dynamic transcriptome analysis. The results showed that 4384 genes were differentially expressed (DEGs) in the two cultivars, displaying significant enrichment of ATP binding, oxidoreductase and hydrolase activity and iron transport. More DEGs were identified between the waterlogging durations and leaf ages, whereas leaf age-specific DEGs were additionally enriched in the photosystem II, thylakoid membrane and carbohydrate binding pathways. A weighted gene co-expression network analysis (WGCNA) of 17669 highly expressed genes was performed to identify hub genes and construct regulatory networks. A cultivar-specific network was dominated by HST1, MLH1 and SYP22 etc., while leaf age-specific networks were largely regulated by chlorophyll metabolism related hub genes CURT1B, PNSL4, and PSY1 etc. This study provided a new insight into deciphering the role of hub genes, networks and pathways with relevance to whole leaves responses to waterlogging stress.

The signaling role of extracellular ATP in co-culture of Shiraia sp. S9 and Pseudomonas fulva SB1 for enhancing hypocrellin A production

BackgroundAdenosine 5′-triphosphate (ATP) plays both a central role as an intracellular energy source, and a crucial extracellular signaling role in diverse physiological processes of animals and plants. However, there are less reports concerning the signaling role of microbial extracellular ATP (eATP). Hypocrellins are effective anticancer photodynamic therapy (PDT) agents from bambusicolous Shiraia fungi. The co-culture of Shiraia sp. S9 and a bacterium Pseudomonas fulva SB1 isolated from Shiraia fruiting bodies was established for enhanced hypocrellin A (HA) production. The signaling roles of eATP to mediate hypocrellin biosynthesis were investigated in the co-culture.ResultsThe co-culture induced release of eATP at 378 nM to the medium around 4 h. The eATP release was interdependent on cytosolic Ca2+ concentration and reactive oxygen species (ROS) production, respectively. The eATP production could be suppressed by the Ca2+ chelator EGTA or abolished by the channel blocker La3+, ROS scavenger vitamin C and NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI). The bacterium-induced H2O2 production was strongly inhibited by reactive blue (RB), a specific inhibitor of membrane purinoceptors, but dependent on the induced Ca2+ influx in the co-culture. On the other hand, the application of exogenous ATP (exATP) at 10–300 µM to Shiraia cultures also promoted fungal conidiation and HA production, both of which were blocked effectively by the purinoceptor inhibitors pyridoxalphosphate-6-azophenyl-2′, 4′-disulfonic acid (PPADS) and RB, and ATP hydrolase apyrase. Both the induced expression of HA biosynthetic genes and HA accumulation were inhibited significantly under the blocking of the eATP or Ca2+ signaling, and the scavenge of ROS in the co-culture.ConclusionsOur results indicate that eATP release is an early event during the intimate bacterial–fungal interaction and eATP plays a signaling role in the bacterial elicitation on fungal metabolites. Ca2+ and ROS are closely linked for activation of the induced ATP release and its signal transduction. This is the first report on eATP production in the fungal–bacterial co-culture and its involvement in the induced biosynthesis of fungal metabolites.Graphic abstract

Intracellular pH regulation: characterization and functional investigation of H+ transporters in Stylophora pistillata

BackgroundReef-building corals regularly experience changes in intra- and extracellular H+ concentrations ([H+]) due to physiological and environmental processes. Stringent control of [H+] is required to maintain the homeostatic acid-base balance in coral cells and is achieved through the regulation of intracellular pH (pHi). This task is especially challenging for reef-building corals that share an endosymbiotic relationship with photosynthetic dinoflagellates (family Symbiodinaceae), which significantly affect the pHi of coral cells. Despite their importance, the pH regulatory proteins involved in the homeostatic acid-base balance have been scarcely investigated in corals. Here, we report in the coral Stylophora pistillata a full characterization of the genomic structure, domain topology and phylogeny of three major H+ transporter families that are known to play a role in the intracellular pH regulation of animal cells; we investigated their tissue-specific expression patterns and assessed the effect of seawater acidification on their expression levels.ResultsWe identified members of the Na+/H+ exchanger (SLC9), vacuolar-type electrogenic H+-ATP hydrolase (V-ATPase) and voltage-gated proton channel (HvCN) families in the genome and transcriptome of S. pistillata. In addition, we identified a novel member of the HvCN gene family in the cnidarian subclass Hexacorallia that has not been previously described in any species. We also identified key residues that contribute to H+ transporter substrate specificity, protein function and regulation. Last, we demonstrated that some of these proteins have different tissue expression patterns, and most are unaffected by exposure to seawater acidification.ConclusionsIn this study, we provide the first characterization of H+ transporters that might contribute to the homeostatic acid-base balance in coral cells. This work will enrich the knowledge of the basic aspects of coral biology and has important implications for our understanding of how corals regulate their intracellular environment.

Circulating Inhibitory Factor 1 levels in adult patients with Prader-Willi syndrome.

Prader-Willi syndrome (PWS) is a rare genetic syndrome characterized by hyperphagia and early development of morbid obesity. Cardiovascular disease (CVD) and metabolic syndrome (MetS) are major comorbidities in these patients leading to premature death. Inhibitory factor 1 (IF1) works as a regulatory protein, inhibiting the ATP hydrolase activity of mitochondrial ATP synthase and likely playing a role in lipid metabolism. We aimed to assay IF1 in adult patients with PWS evaluating any relationship with clinical, genetic and biochemical parameters. We recruited 35 adult patients with genetically confirmed PWS. IF1 serum concentration displayed a normal distribution with an average value of 70.7±22.6pg/mL, a median value of 66.1pg/mL. It was above the reference range only in one patient. All parameters were compared from both sides of IF1 median without displaying any significant differences. Patients with normal or low HDL-cholesterol did not present any difference as regards IF1 levels, which were not different between patients with and without MetS. Non-esterified fatty acids (NEFA) serum levels (r=0.623; p<0.001) showed a statistically significant correlation with IF1. Cholesterol and its fractions did not present any correlation with IF1. In this study we do not confirm that HDL-cholesterol and IF1 are correlated, but we show that in adult PWS patients, NEFA are correlated with serum IF1. This protein could play a role to some extent in determining the complex metabolic alterations in PWS patients.

Regulation of bacterial ATP synthase activity: A gear-shifting or a pawl-ratchet mechanism?

The F1 Fo -ATP synthase, a widely distributed nanomotor responsible of ATP synthesis, rotates its central rotor reversibly: In the clockwise direction when viewed from the Fo (with the observer facing the positive side of the energy transducing membrane and looking down into the negative side of the membrane), it functions as ATP synthase, while in counterclockwise sense, it operates as a proton-pumping ATP hydrolase. Regulation exerted by naturally occurring inhibitory proteins of the enzyme appears to function by avoiding ATP hydrolysis while preserving ATP synthesis. The work of Liu et al. describes an unbiased, elegant analytical pipeline that provides important insights into the inhibitory role of the ε-subunit of the bacterial F1 Fo -ATP synthase invivo. We discuss if a gear-shifting versus a pawl-ratchet mechanism may explain the regulatory role of the ε-subunit.

Effects of light intensity on material and energy metabolism of Viola yedoensis

Light energy is an important factor affecting plant growth. The hypothesis of &quot;light-cold and heat property&quot; holds that the original plants of traditional Chinese medicines(TCM) with cold property can obtain more energy to maintain growth in high light intensity environment, whereas the original plants of TCM with heat property prefer weak light environment. The current experiment investigated the effects of different light intensities on primary metabolites levels, energy levels, cell apoptosis, and leaves ultrastructure of Viola yedoensis, the original plants of TCM Violae Herba with cold property. There were five treatment groups of V. yedoensis, which was planted under Li1(8 500 lx),Li2(7 250 lx),Li3(6 000 lx),Li4(4 750 lx),Li5(3 500 lx)LEDs light intensity conditions, respectively. After harvest, primary metabolites levels, contents of ATP, ADP, AMP, activities of ATP synthesis and hydrolysis related enzyme, as well as cell apoptosis activation degree were measured, and transmission electron microscopy technique was used to observe leaves ultrastructure. The results showed that the total sugar, total protein, contents of ATP, ADP and AMP, activities of NADH dehydrogenase, cytochrome C reductase, ATP synthase and ATP hydrolase were positively correlated with light intensities(P&lt;0.05). The crude fat content, activities of SDH and CCO enzyme showed a trend of increasing first and then decreasing, the highest value were found in Li2 group and Li3 group respectively(P&lt;0.05). The vitality of caspase-3 and caspase-9 was negatively correlated with light intensities(P&lt;0.05). The structure of chloroplast and mitochondria were normal and intact in Li1-Li3 groups, and the damage degree of Li4 and Li5 groups increased with the decrease of light intensities. The analysis of results indicated that the structure of chloroplast and mitochondria of V. yedoensis is normal under the light intensity of 6 000-8 500 lx, which can obtain more energy to maintain its growth and metabolism. When the light intensity is lower than 4 750 lx, the chloroplast morphology and mitochondrial membrane are damaged, affecting the metabolism of material and energy. There was no significant difference in energy charge of V. yedoensis in the light intensity range of 3 500～8 500 lx. The effect of light intensity on energy metabolism of V. yedoensis accords with the hypothesis of &quot;light-cold and heat property&quot;.

ANT2-Mediated ATP Import into Mitochondria Protects against Hypoxia Lethal Injury

Following a prolonged exposure to hypoxia–reoxygenation, a partial disruption of the ER-mitochondria tethering by mitofusin 2 (MFN2) knock-down decreases the Ca2+ transfer between the two organelles limits mitochondrial Ca2+ overload and prevents the Ca2+-dependent opening of the mitochondrial permeability transition pore, i.e., limits cardiomyocyte cell death. The impact of the metabolic changes resulting from the alteration of this Ca2+crosstalk on the tolerance to hypoxia–reoxygenation injury remains partial and fragmented between different field of expertise. >In this study, we report that MFN2 loss of function results in a metabolic switch driven by major modifications in energy production by mitochondria. During hypoxia, mitochondria maintain their ATP concentration and, concomitantly, the inner membrane potential by importing cytosolic ATP into mitochondria through an overexpressed ANT2 protein and by decreasing the expression and activity of the ATP hydrolase via IF1. This adaptation further blunts the detrimental hyperpolarisation of the inner mitochondrial membrane (IMM) upon re-oxygenation. These metabolic changes play an important role to attenuate cell death during a prolonged hypoxia–reoxygenation challenge.

Hydrolytic activity of mitochondrial F1Fo ATP synthase as a target for myocardial ischemia: discovery and in vitro evaluation of novel inhibitors

Abstract Background/Introduction F1Fo ATP synthase is the mitochondrial complex responsible for ATP production. During myocardial ischemia, ATP synthase reverses its activity to hydrolyse ATP leading to cellular energetic deficit, contracture and lethal cardiomyocyte injury. Therefore, inhibition of ATP hydrolase is of major significance and the discovery of selective hydrolase inhibitors could be of particular interest in terms of cardiac response to ischemia. Purpose We performed an in vitro screening in order to identify and evaluate novel specific inhibitors of the hydrolytic activity of ATP synthase. Methods Initially, we identified inhibitors of the hydrolytic activity of ATP synthase using virtual screening methods. Docking-scoring calculations were performed targeting the three major inhibition sites of a holistic model of ATP synthase of mus musculus that was modelled for the first time. In silico ligand-based virtual screening was carried out using known binders such as BMS199264. The workflow was implemented on our in-house library of 2000 compounds, Pharmalab, plus 266,151 compounds of the National Cancer Institute (NCI) database. The best candidates were evaluated in vitro on isolated murine heart mitochondria to verify their inhibitory effect on ATP synthase hydrolytic activity. Moreover, we confirmed their action at a cellular level. H9C2 cells were treated with the three best candidates in the presence of rotenone and their ability to maintain membrane potential was monitored. The experiment was repeated in absence of rotenone in order to detect toxic or non-specific effects (n=5 independent experiments). Finally, the compounds were tested using an assay in which primary adult rat ventricular cardiomyocytes (ARVCs) were challenged with the mitochondrial uncoupler CCCP to induce reverse ATPase activity, and time until contracture was determined. For the in vitro experiments, oligomycin, a non-selective ATPase inhibitor and BTB06584 a selective hydrolase inhibitor were used as positive controls. Results Different steps of filtering through the virtual screening provided 38 molecules from Pharmalab and 15 candidates form NCI database. From the 53 candidates in total, five compounds displayed in vitro inhibitory activity at 200μM on isolated mitochondria and their IC50 values were determined. Among them, three synthetic derivatives possessing a central pyrazolopyridine core displayed the best IC50 values (81.7±1.3 μM, 99.8±1.2 μM, 144.8±1.3μM) and were evaluated on the H9C2 cells. They exhibited significant inhibitory activity at 50μM (p&amp;lt;0.01 compared to vehicle) while the BTB06584 inhibitor was inactive at the same concentration and two of them were selective. Finally, the final novel inhibitors significantly extended (p&amp;lt;0.001) the time until shortening of the ARVCs. Conclusion We have discovered two novel agents that act as selective inhibitors of ATP hydrolase and can be tested against myocardial ischemia. Funding Acknowledgement Type of funding source: None

ATP hydrolysis by yeast Hsp104 determines protein aggregate dissolution and size in vivo

Signs of proteostasis failure often entwine with those of metabolic stress at the cellular level. Here, we study protein sequestration during glucose deprivation-induced ATP decline in Saccharomyces cerevisiae. Using live-cell imaging, we find that sequestration of misfolded proteins and nascent polypeptides into two distinct compartments, stress granules, and Q-bodies, is triggered by the exhaustion of ATP. Both compartments readily dissolve in a PKA-dependent manner within minutes of glucose reintroduction and ATP level restoration. We identify the ATP hydrolase activity of Hsp104 disaggregase as the critical ATP-consuming process determining compartments abundance and size, even in optimal conditions. Sequestration of proteins into distinct compartments during acute metabolic stress and their retrieval during the recovery phase provide a competitive fitness advantage, likely promoting cell survival during stress.

Electrogenesis in Plasma Membrane Fraction of Halotolerant Microalga Dunaliella maritima and Effects of N,N′-Dicyclohexylcarbodiimide

The effects of N,N'-dicyclohexylcarbodiimide (DCCD), non-specific inhibitor of various transport systems functioning in biological membranes, on Na+-transporting P-type ATPase of the green halotolerant microalga Dunaliella maritima were studied in the experiments with vesicular plasma membranes isolated from the alga cells. The effects of DCCD on electrogenic/ion transport function of the enzyme and its ATP hydrolase activity were investigated. Electrogenic/ion transport function of the enzyme was recorded as a Na+-dependent generation of electric potential on the vesicle membranes with the help of the potential-sensitive probe oxonol VI. It was found that unlike many other ion-transporting ATPases, the Na+-ATPase of D. maritima is insensitive to DCCD. This agent did not inhibit either ATP hydrolysis catalyzed by this enzyme or its transport activity. At the same time DCCD affected the ability of the vesicle membranes to maintain electric potential generated by the D. maritima Na+-ATPase. The observed effects can be explained based on the assumption that DCCD interacts with the Na+/H+ antiporter in the plasma membrane of D. maritima.

The spatio-temporal organization of mitochondrial F1FO ATP synthase in cristae depends on its activity mode

F1FO ATP synthase, also known as complex V, is a key enzyme of mitochondrial energy metabolism that can synthesize and hydrolyze ATP. It is not known whether the ATP synthase and ATPase function are correlated with a different spatio-temporal organisation of the enzyme. In order to analyze this, we tracked and localized single ATP synthase molecules in situ using live cell microscopy. Under normal conditions, complex V was mainly restricted to cristae indicated by orthogonal trajectories along the cristae membranes. In addition confined trajectories that are quasi immobile exist. By inhibiting glycolysis with 2-DG, the activity and mobility of complex V was altered. The distinct cristae-related orthogonal trajectories of complex V were obliterated. Moreover, a mobile subpopulation of complex V was found in the inner boundary membrane. The observed changes in the ratio of dimeric/monomeric complex V, respectively less mobile/more mobile complex V and its activity changes were reversible. In IF1-KO cells, in which ATP hydrolysis is not inhibited by IF1, complex V was more mobile, while inhibition of ATP hydrolysis by BMS-199264 reduced the mobility of complex V. Taken together, these data support the existence of different subpopulations of complex V, ATP synthase and ATP hydrolase, the latter with higher mobility and probably not prevailing at the cristae edges. Obviously, complex V reacts quickly and reversibly to metabolic conditions, not only by functional, but also by spatial and structural reorganization.