Use of fluorinated tyrosine phosphates to probe the substrate specificity of the low molecular weight phosphatase activity of calcineurin

Endothelin-1 acutely increases nitric oxide production via the calcineurin mediated dephosphorylation of Caveolin-1

Endothelin (ET)-1 is an endothelial-derived peptide that exerts biphasic effects on nitric oxide (NO) levels in endothelial cells such that acute exposure stimulates-while sustained exposure attenuates-NO production. Although the mechanism involved in the decrease in NO generation has been identified but the signaling involved in the acute increase in NO is still unresolved. This was the focus of this study. Our data indicate that exposing pulmonary arterial endothelial cells (PAEC) to ET-1 led to an increase in NO for up to 30min after which levels declined. These effects were attenuated by ET receptor antagonists. The increase in NO correlated with significant increases in pp60Src activity and increases in eNOS phosphorylation at Tyr83 and Ser1177. The ET-1 mediated increase in phosphorylation and NO generation were attenuated by the over-expression of a pp60Src dominant negative mutant. The increase in pp60Src activity correlated with a reduction in the interaction of Caveolin-1 with pp60Src and the calcineurin-mediated dephosphorylation of caveolin-1 at three previously unidentified sites: Thr91, Thr93, and Thr95. The calcineurin inhibitor, Tacrolimus, attenuated the acute increase in pp60Src activity induced by ET-1 and a calcineurin siRNA attenuated the ET-1 mediated increase in eNOS phosphorylation at Tyr83 and Ser1177 as well as the increase in NO. By using a Caveolin-1 celluSpot peptide array, we identified a peptide targeting a sequence located between aa 41-56 as the pp60Src binding region. This peptide fused to the TAT sequence was found to decrease caveolin-pp60Src interaction, increased pp60Src activity, increased eNOS pSer1177 and NO levels in PAEC and induce vasodilation in isolated aortic rings in wildtype but not eNOS knockout mice. Together, our data identify a novel mechanism by which ET-1 acutely increases NO via a calcineurin-mediated dephosphorylation of caveolin-1 and the subsequent stimulation of pp60Src activity, leading to increases in phosphorylation of eNOS at Tyr83 and Ser1177.

The PtdIns3P phosphatase MtMP promotes symbiotic nitrogen fixation via mitophagy in Medicago truncatula

Symbiotic nitrogen fixation is a complex process in which legumes interact with rhizobia under nitrogen starvation. In this study, we found that myotubularin phosphatase (MtMP) is mainly expressed in roots and nodules in Medicago truncatula. MtMP promotes autophagy by dephosphorylating PtdIns3P on autophagosomes. The mp mutants inoculated with rhizobia showed a significant reduction in nitrogenase activity and significantly higher number of mitochondria than those of wild-type plants under nitrogen starvation, indicating that MtMP is involved in mitophagy of the infection zone. Mitophagy may provide carbon skeletons and nitrogen for the development of bacteroids and the reprogramming of infected cells. In conclusion, we found, for the first time, that myotubularin phosphatase is involved in autophagy in plants. MtMP-involved autophagy plays an active role in symbiotic nitrogen fixation. These results deepen our understanding of symbiotic nitrogen fixation.

Colorimetry-Based Phosphate Measurement for Polymerase Elongation

DNA detection, which includes the measurement of variants in sequences or the presence of certain genes, is widely used in research and clinical diagnosis. Both require DNA-dependent DNA polymerase-catalyzed strand extension. Currently, these techniques rely heavily on the instruments used to visualize the results. This study introduced a simple and direct colorimetric method to measure polymerase-directed elongation. First, pyrophosphate (PPi), a by-product of strand extension, is converted into phosphate (Pi). Phosphate levels were measured using either Mo-Sb or BIOMOL Green reagent. This study showed that this colorimetry can distinguish single-base variants and detect PCR products in preset stringent conditions, implicating the potential value of this strategy to detect DNA.

Identification of the inhibitory mechanism of ecumicin and rufomycin 4-7 on the proteolytic activity of Mycobacterium tuberculosis ClpC1/ClpP1/ClpP2 complex

Ecumicin and rufomycin 4-7 disrupt protein homeostasis in Mycobacterium tuberculosis by inhibiting the proteolytic activity of the ClpC1/ClpP1/ClpP2 complex. Although these compounds target ClpC1, their effects on the ATPase activity of ClpC1 and proteolytic activity of ClpC1/ClpP1/ClpP2 vary. Herein, we explored the ClpC1 molecular dynamics with these compounds through fluorescence correlation spectroscopy. The effect of these compounds on the ATPase activity of ClpC1-cys, the recombinant protein for fluorescence labeling, and proteolytic activity of ClpC1-cys/ClpP1/ClpP2 were identical to those of native ClpC1, whereas the intermolecular dynamics of fluorescence-labelled ClpC1 were different. Treatment with up to 1 nM ecumicin increased the population of slower diffused ClpC1 components compared with ClpC1 without ecumicin. However, this population was considerably reduced when treated with 10 nM ecumicin. Rufomycin 4-7 treatment resulted in a slower diffused component of ClpC1, and the portion of this component increased in a concentration-dependent manner. Ecumicin can generate an abnormal ClpC1 component, which cannot form normal ClpC1/ClpP1/ClpP2, via two different modes. Rufomycin 4-7 only generates slower diffused ClpC1 component that is inadequate to form normal ClpC1/ClpP1/ClpP2. Overall, we demonstrate that ecumicin and rufomycin 4-7 use different action mechanisms to generate abnormal ClpC1 components that cannot couple with ClpP1/ClpP2.

Virtual Screening Based Discovery of PTP1B Inhibitors and Their Biological Evaluations

Background :

The discovery of novel antidiabetics for the treatment of type 2 diabetes mellitus (T2DM) is an important task nowadays because the current treatment approaches have certain limitations. The reported studies showed that the protein tyrosine phosphatase 1B (PTP1B) is a valuable target, can be used to develop significant antidiabetic molecules.

Objective:

In the present investigation, computational methods and biological evaluation studies have been applied to develop novel PTP1B inhibitors with good enzyme binding affinity and activity.

Methods:

Virtual screening (docking) analysis of SPECS database compounds on PTP1B enzyme was performed using Schrodinger software. In vitro and in vivo biological evaluations had been conducted with the identified hits.

Results:

The results revealed that the molecules identified through these studies have shown significant interactions with the active site residues of the PTP1B enzyme. The compounds S1 and S2 provided significant binding interactions with the residues (Arg221 and Gln262) and have shown considerable in vitro PTP1B inhibitory activity and in vivo antidiabetic activity. The compounds S1 and S2 possessed 35.44±0.12% and 33.68±0.08% inhibitory activities, respectively.

Conclusion:

These identified hits will be used as a template for design and development of novel PTP1B inhibitors with a compatible pharmacokinetic profile.

Altering of host larval (Spodoptera exigua) calcineurin activity in response to ascovirus infection

BACKGROUND

Calcineurin (CaN) is involved in numerous cellular processes and Ca²⁺ -dependent signal transduction pathways. According to our previous transcriptome studies, thousands of host larval (Spodoptera exigua) transcripts were downregulated after the infection of Heliothis virescent ascovirus 3h (HvAV-3h), while the Spodoptera exigua calcineurin genes (SeCaNs) were significantly upregulated. To understand the regulation of SeCaNs in S. exigua larvae during the infection of HvAV-3h, the functions of CaN subunit A (SeCaN-SubA) and CaN binding protein (SeCaN-BP) were analysed.

RESULTS

The in vitro assays indicated that the bacterial expressed SeCaN-SubA is an acid phosphatase, but no phosphatase activity was detected with the purified SeCaN-BP. The transcription level of SeCaN-SubA was upregulated after HvAV-3h infection and the CaN activity was significantly increased after HvAV-3h infection in S. exigua larvae. Interestingly, the SeCaN-BP transcripts were only detectable in the HvAV-3h infected larvae. Further immunoblotting results consistently agree with those obtained by qPCR, indicating that the infection of HvAV-3h causes the upregulated expression of SeCaN-SubA and the appearance of SeCaN-BP. An interaction between the cleaved SeCaN-SubA and SeCaN-BP was detected by co-immunoprecipitation assays, and the expression of SeCaN-BP in Spodoptera frugiperda-9 (Sf9) cells can help to increase the CaN activity of SeCaN-SubA. Further investigations with CaN inhibitors suggested that HvAV-3h. Further investigations with CaN inhibitors suggested that the inhibition on host larval CaN activity can also inhibit the viral replication of HvAV-3h.

CONCLUSION

The increase in CaN activity caused by HvAV-3h infection might be due to the upregulation of SeCaN-SubA and the induced expression of SeCaN-BP, and increased CaN activity is essential for ascoviral replication. © 2019 Society of Chemical Industry.

Physiologically relevant orthogonal assays for the discovery of small-molecule modulators of WIP1 phosphatase in high-throughput screens

WT P53-Induced Phosphatase 1 (WIP1) is a member of the magnesium-dependent serine/threonine protein phosphatase (PPM) family and is induced by P53 in response to DNA damage. In several human cancers, the WIP1 protein is overexpressed, which is generally associated with a worse prognosis. Although WIP1 is an attractive therapeutic target, no potent, selective, and bioactive small-molecule modulator with favorable pharmacokinetics has been reported. Phosphatase enzymes are among the most challenging targets for small molecules because of the difficulty of achieving both modulator selectivity and bioavailability. Another major obstacle has been the availability of robust and physiologically relevant phosphatase assays that are suitable for high-throughput screening. Here, we describe orthogonal biochemical WIP1 activity assays that utilize phosphopeptides from native WIP1 substrates. We optimized an MS assay to quantify the enzymatically dephosphorylated peptide reaction product in a 384-well format. Additionally, a red-shifted fluorescence assay was optimized in a 1,536-well format to enable real-time WIP1 activity measurements through the detection of the orthogonal reaction product, P_i. We validated these two optimized assays by quantitative high-throughput screening against the National Center for Advancing Translational Sciences (NCATS) Pharmaceutical Collection and used secondary assays to confirm and evaluate inhibitors identified in the primary screen. Five inhibitors were further tested with an orthogonal WIP1 activity assay and surface plasmon resonance binding studies. Our results validate the application of miniaturized physiologically relevant and orthogonal WIP1 activity assays to discover small-molecule modulators from high-throughput screens.

Inhibitors of Serine/Threonine Protein Phosphatases: Biochemical and Structural Studies Provide Insight for Further Development

BACKGROUND

The reversible phosphorylation of proteins regulates many key functions in eukaryotic cells. Phosphorylation is catalyzed by protein kinases, with the majority of phosphorylation occurring on side chains of serine and threonine residues. The phosphomonoesters generated by protein kinases are hydrolyzed by protein phosphatases. In the absence of a phosphatase, the half-time for the hydrolysis of alkyl phosphate dianions at 25º C is over 1 trillion years; knon ~2 x 10-20 sec-1. Therefore, ser/thr phosphatases are critical for processes controlled by reversible phosphorylation.

METHODS

This review is based on the literature searched in available databases. We compare the catalytic mechanism of PPP-family phosphatases (PPPases) and the interactions of inhibitors that target these enzymes.

RESULTS

PPPases are metal-dependent hydrolases that enhance the rate of hydrolysis ([kcat/kM]/knon ) by a factor of ~1021, placing them among the most powerful known catalysts on earth. Biochemical and structural studies indicate that the remarkable catalytic proficiencies of PPPases are achieved by 10 conserved amino acids, DXH(X)~26DXXDR(X)~20- 26NH(X)~50H(X)~25-45R(X)~30-40H. Six act as metal-coordinating residues. Four position and orient the substrate phosphate. Together, two metal ions and the 10 catalytic residues position the phosphoryl group and an activated bridging water/hydroxide nucleophile for an inline attack upon the substrate phosphorous atom. The PPPases are conserved among species, and many structurally diverse natural toxins co-evolved to target these enzymes.

CONCLUSION

Although the catalytic site is conserved, opportunities for the development of selective inhibitors of this important group of metalloenzymes exist.

Synthesis, biological evaluation and in silico studies of 5-(3-methoxybenzylidene)thiazolidine-2,4-dione analogues as PTP1B inhibitors

PTP1B (protein tyrosine phosphatase 1B) dephosphorylates the insulin receptor substrate and thus acts as a negative regulator of the insulin and leptin signalling pathway. Recently, it has been considered as a new therapeutic target of intervention for the treatment of type2 diabetes. A series of aryl/alkylsulfonyloxy-5-(3-methoxybenzylidene)thiazolidine-2,4-dione derivatives were synthesized, screened in vitro for their PTP1B inhibitory activity and in vivo for anti-hyperglycaemic activity. Docking results further helped in understanding the nature of interactions governing the binding mode of ligands inside the active site of PTP1B. Among the synthesized compounds, 13 and 16 were found to be potent PTP1B inhibitors having IC₅₀ of 7.31 and 8.73μM respectively. Significant lowering of blood glucose level was observed in some of the synthesized compounds in in vivo study.

Application of a Euryarchaeota-Specific Helicase from Thermococcus kodakarensis for Noise Reduction in PCR

DNA/RNA helicases, which are enzymes for eliminating hydrogen bonds between bases of DNA/DNA, DNA/RNA, and RNA/RNA using the energy of ATP hydrolysis, contribute to various biological activities. In the present study, the Euryarchaeota-specific helicase EshA (TK0566) from the hyperthermophilic archaeon Thermococcus kodakarensis (Tk-EshA) was obtained as a recombinant form, and its enzymatic properties were examined. Tk-EshA exhibited maximal ATPase activity in the presence of RNA at 80°C. Unwinding activity was evaluated with various double-stranded DNAs (forked, 5' overhung, 3' overhung, and blunt end) at 50°C. Tk-EshA unwound forked and 3' overhung DNAs. These activities were expected to unwind the structured template and to peel off misannealed primers when Tk-EshA was added to a PCR mixture. To examine the effect of Tk-EshA on PCR, various target DNAs were selected, and DNA synthesis was investigated. When 16S rRNA genes were used as a template, several misamplified products (noise DNAs) were detected in the absence of Tk-EshA. In contrast, noise DNAs were eliminated in the presence of Tk-EshA. Noise reduction by Tk-EshA was also confirmed when Taq DNA polymerase (a family A DNA polymerase, PolI type) and KOD DNA polymerase (a family B DNA polymerase, α type) were used for PCR. Misamplified bands were also eliminated during toxA gene amplification from Pseudomonas aeruginosa DNA, which possesses a high GC content (69%). Tk-EshA addition was more effective than increasing the annealing temperature to reduce misamplified DNAs during toxA amplification. Tk-EshA is a useful tool to reduce noise DNAs for accurate PCR.

IMPORTANCE

PCR is a technique that is useful for genetic diagnosis, genetic engineering, and detection of pathogenic microorganisms. However, troubles with nonspecific DNA amplification often occur from primer misannealing. In order to achieve a specific DNA amplification by eliminating noise DNAs derived from primer misannealing, a thermostable Euryarchaeota-specific helicase (Tk-EshA) was included in the PCR mixture. The addition of Tk-EshA has reduced noise DNAs in PCR.

New strategy of tacrolimus administration in animal model based on tacrolimus-loaded microspheres

New strategies for tacrolimus administration that conserve its immunosuppressive effect but avoiding fluctuations in tacrolimus circulating levels are needed. The aim was to analyze if subcutaneous biodegradable tacrolimus-loaded microspheres injection promoted a significant immunosuppressive response in rats. Rats received two subcutaneous tacrolimus-loaded microspheres injections at different days, the first injection was done at day 0 and the second injection was done 12 days after. Plasma circulating levels of tacrolimus, interleukin-2 (IL-2) and calcineurin phosphatase (PP2B) activity in mononuclear cells were measured. Tacrolimus plasma levels were significantly increased from the day after tacrolimus-loaded microspheres injection and remained increased during 10days. Compared to control, plasma IL-2 levels and PP2B activity in mononuclear cells were significantly decreased during ten days. At day 12, a new subcutaneous injection of tacrolimus-loaded microspheres was performed and two days after injection, tacrolimus plasma levels were again increased and both IL-2 plasma levels and PP2B activity decreased. A single subcutaneous tacrolimus-loaded microspheres injection was enough to reduce tacrolimus-related immunosuppressive parameters. These results open the possibility of new therapeutic strategies to administrate calcineurin inhibitors reducing the variability of their circulating levels related to gastrointestinal drug absorption/metabolism modifications.

Mechanism of DNA loading by the DNA repair helicase XPD

The xeroderma pigmentosum group D (XPD) helicase is a component of the transcription factor IIH complex in eukaryotes and plays an essential role in DNA repair in the nucleotide excision repair pathway. XPD is a 5′ to 3′ helicase with an essential iron–sulfur cluster. Structural and biochemical studies of the monomeric archaeal XPD homologues have aided a mechanistic understanding of this important class of helicase, but several important questions remain open. In particular, the mechanism for DNA loading, which is assumed to require large protein conformational change, is not fully understood. Here, DNA binding by the archaeal XPD helicase from Thermoplasma acidophilum has been investigated using a combination of crystallography, cross-linking, modified substrates and biochemical assays. The data are consistent with an initial tight binding of ssDNA to helicase domain 2, followed by transient opening of the interface between the Arch and 4FeS domains, allowing access to a second binding site on helicase domain 1 that directs DNA through the pore. A crystal structure of XPD from Sulfolobus acidocaldiarius that lacks helicase domain 2 has an otherwise unperturbed structure, emphasizing the stability of the interface between the Arch and 4FeS domains in XPD.

The calcineurin antagonist RCAN1-4 is induced by exhaustive exercise in rat skeletal muscle

The aim of this work was to study the regulation of the calcineurin antagonist regulator of calcineurin 1 (RCAN1) in rat skeletal muscles after exhaustive physical exercise, which is a physiological modulator of oxidative stress. Three skeletal muscles, namely extensor digitorum longus (EDL), gastrocnemius, and soleus, were investigated. Exhaustive exercise increased RCAN1-4 protein levels in EDL and gastrocnemius, but not in soleus. Protein oxidation as an index of oxidative stress was increased in EDL and gastrocnemius, but remained unchanged in soleus. However, lipid peroxidation was increased in all three muscles. CuZnSOD and catalase protein levels were increased at 3 h postexercise in soleus, whereas they remained unchanged in EDL and gastrocnemius. Calcineurin enzymatic activity declined in EDL and gastrocnemius but not in soleus, and its protein expression was decreased in all three muscles. The level of PGC1-α protein remained unchanged, whereas the protein expression of the transcription factor NFATc4 was decreased in all three muscles. Adiponectin expression was increased in all three muscles. RCAN1-4 expression in EDL and gastrocnemius muscles was augmented by the oxidative stress generated from exhaustive exercise. We propose that increased RCAN1-4 expression and the signal transduction pathways it regulates represent important components of the physiological adaptation to exercise-induced oxidative stress.

Prolonged Subcutaneous Administration of Oxytocin Accelerates Angiotensin II-Induced Hypertension and Renal Damage in Male Rats

Oxytocin and its receptor are synthesised in the heart and blood vessels but effects of chronic activation of this peripheral oxytocinergic system on cardiovascular function are not known. In acute studies, systemic administration of low dose oxytocin exerted a protective, preconditioning effect in experimental models of myocardial ischemia and infarction. In this study, we investigated the effects of chronic administration of low dose oxytocin following angiotensin II-induced hypertension, cardiac hypertrophy and renal damage. Angiotensin II (40 μg/Kg/h) only, oxytocin only (20 or 100 ng/Kg/h), or angiotensin II combined with oxytocin (20 or 100 ng/Kg/h) were infused subcutaneously in adult male Sprague-Dawley rats for 28 days. At day 7, oxytocin or angiotensin-II only did not change hemodynamic parameters, but animals that received a combination of oxytocin and angiotensin-II had significantly elevated systolic, diastolic and mean arterial pressure compared to controls (P < 0.01). Hemodynamic changes were accompanied by significant left ventricular cardiac hypertrophy and renal damage at day 28 in animals treated with angiotensin II (P < 0.05) or both oxytocin and angiotensin II, compared to controls (P < 0.01). Prolonged oxytocin administration did not affect plasma concentrations of renin and atrial natriuretic peptide, but was associated with the activation of calcium-dependent protein phosphatase calcineurin, a canonical signalling mechanism in pressure overload-induced cardiovascular disease. These data demonstrate that oxytocin accelerated angiotensin-II induced hypertension and end-organ renal damage, suggesting caution should be exercised in the chronic use of oxytocin in individuals with hypertension.

A Mutant Chaperonin That Is Functional at Lower Temperatures Enables Hyperthermophilic Archaea To Grow under Cold-Stress Conditions

Thermococcus kodakarensis grows optimally at 85°C and possesses two chaperonins, cold-inducible CpkA and heat-inducible CpkB, which are involved in adaptation to low and high temperatures, respectively. The two chaperonins share a high sequence identity (77%), except in their C-terminal regions. CpkA, which contains tandem repeats of a GGM motif, shows its highest ATPase activity at 60°C to 70°C, whereas CpkB shows its highest activity at temperatures higher than 90°C. To clarify the effects of changes in ATPase activity on chaperonin function at lower temperatures, various CpkA variants were constructed by introducing single point mutations into the C-terminal region. A CpkA variant in which Glu530 was replaced with Gly (CpkA-E530G) showed increased ATPase activity, with its highest activity at 50°C. The efficacy of the CpkA variants against denatured indole-3-glycerol-phosphate synthase of T. kodakarensis (TrpCTk), which is a CpkA target, was then examined in vitro. CpkA-E530G was more effective than wild-type CpkA at facilitating the refolding of chemically unfolded TrpCTk at 50°C. The effect of cpkA-E530G on cell growth was then examined by introducing cpkA-E530G into the genome of T. kodakarensis KU216 (pyrF). The mutant strain, DA4 (pyrF cpkA-E530G), grew as well as the parental KU216 strain at 60°C. In contrast, DA4 grew more vigorously than KU216 at 50°C. These results suggested that the CpkA-E530G mutation prevented cold denaturation of proteins under cold-stress conditions, thereby enabling cells to grow in cooler environments. Thus, a single base pair substitution in a chaperonin gene allows cells to grow vigorously in a new environment.

IMPORTANCE

Thermococcus kodakarensis possesses two group II chaperonins, cold-inducible CpkA and heat-inducible CpkB, which are involved in adaptation to low and high temperatures, respectively. CpkA might act as an "adaptive allele" to adapt to cooler environments. In this study, we compared the last 20 amino acids within the C termini of the chaperonins and found a clear correlation between the CpkA-type chaperonin gene copy number and growth temperature. Furthermore, we introduced single mutations into the CpkA C-terminal region to clarify its role in cold adaptation, and we showed that a single base substitution allowed the organism to adapt to a lower temperature. The present data suggest that hyperthermophiles have evolved by obtaining mutations in chaperonins that allow them to adapt to a colder environment.

A continuous tyrosyl-tRNA synthetase assay that regenerates the tRNA substrate

Tyrosyl-tRNA synthetase catalyzes the attachment of tyrosine to the 3' end of tRNA(Tyr), releasing AMP, pyrophosphate, and l-tyrosyl-tRNA as products. Because this enzyme plays a central role in protein synthesis, it has garnered attention as a potential target for the development of novel antimicrobial agents. Although high-throughput assays that monitor tyrosyl-tRNA synthetase activity have been described, these assays generally use stoichiometric amounts of tRNA, limiting their sensitivity and increasing their cost. Here, we describe an alternate approach in which the Tyr-tRNA product is cleaved, regenerating the free tRNA substrate. We show that cyclodityrosine synthase from Mycobacterium tuberculosis can be used to cleave the l-Tyr-tRNA product, regenerating the tRNA(Tyr) substrate. Because tyrosyl-tRNA synthetase can use both l- and d-tyrosine as substrates, we replaced the cyclodityrosine synthase in the assay with d-tyrosyl-tRNA deacylase, which cleaves d-Tyr-tRNA. This substitution allowed us to use the tyrosyl-tRNA synthetase assay to monitor the aminoacylation of tRNA(Tyr) by d-tyrosine. Furthermore, by making Tyr-tRNA cleavage the rate-limiting step, we are able to use the assay to monitor the activities of cyclodityrosine synthetase and d-tyrosyl-tRNA deacylase. Specific methods to extend the tyrosyl-tRNA synthetase assay to monitor both the aminoacylation and post-transfer editing activities in other aminoacyl-tRNA synthetases are discussed.

Analysis of intracellular PTEN signaling and secretion

The tumor suppressor PTEN dephosphorylates PIP3 to inhibit PI3K signaling in cells. Altering PTEN intracellular signaling can therefore significantly affect cell behavior. Two novel mechanisms of PTEN regulation including the secretion and entry of the translational variant PTEN-L, and enzymatic inhibition by the interacting protein P-REX2, have been shown to modulate PI3K signaling, cellular proliferation and survival, and glucose metabolism. Here, we review the methods used to identify and validate the existence of both PTEN-L and the P-REX2-PTEN complex, to determine their effects on PTEN phosphatase activity, and to examine their role in cellular physiology.

Small molecule Plasmodium FKBP35 inhibitor as a potential antimalaria agent

Malaria parasite strains have emerged to tolerate the therapeutic effects of the prophylactics and drugs presently available. This resistance now poses a serious challenge to researchers in the bid to overcome malaria parasitic infection. Recent studies have shown that FK520 and its analogs inhibit malaria parasites growth by binding to FK506 binding proteins (FKBPs) of the parasites. Structure based drug screening efforts based on three-dimensional structural information of FKBPs from Plasmodium falciparum led us to identify new chemical entities that bind to the parasite FKBP35 and inhibit its growth. Our experimental results verify that this novel compound (D44) modulate the PPIase activity of Plasmodium FKBP35 and demonstrate the stage-specific growth inhibition of Plasmodium falciparum strains. Here, we present the X-ray crystallographic structures of FK506 binding domains (FKBDs) of PfFKBP35 and PvFKBP35 in complex with the newly identified inhibitor providing molecular insights into its mode of action.

Role of calcineurin and actin dynamics in regulated secretion of microneme proteins in Plasmodium falciparum merozoites during erythrocyte invasion

Plasmodium falciparum invades host erythrocytes by multiple invasion pathways. The invasion of erythrocytes by P. falciparum merozoites is a complex process that requires multiple interactions between host receptors and parasite ligands. A number of parasite proteins that mediate interaction with host receptors during invasion are localized to membrane-bound apical organelles referred to as micronemes and rhoptries. The timely release of these proteins to the merozoite surface is crucial for receptor engagement and invasion. It has been demonstrated previously that exposure of merozoites to a low potassium (K(+)) ionic environment as found in blood plasma leads to a rise in cytosolic calcium (Ca(2+)), which triggers microneme secretion. The signalling pathways that regulate microneme discharge in response to rise in cytosolic Ca(2+) are not completely understood. Here, we show that a P. falciparum Ca(2+)-dependent protein phosphatase, calcineurin (PfCN), is an essential regulator of Ca(2+)-dependent microneme exocytosis. An increase in PfCN activity was observed in merozoites following exposure to a low K(+) environment. Treatment of merozoites with calcineurin inhibitors such as FK506 and cyclosporin A prior to transfer to a low K(+) environment resulted in inhibition of secretion of microneme protein apical merozoite antigen-1 (PfAMA-1). Inhibition of PfCN was shown to result in reduced dephosphorylation and depolymerization of apical actin, which appears to be criticalfor microneme secretion. PfCN thus serves as an effector of Ca(2+)-dependent microneme exocytosis by regulating depolymerization of apical actin. Inhibitors that target PfCN block microneme exocytosis and limit growth of P. falciparum blood-stage parasites providing a novel approach towards development of new therapeutic strategies against malaria.

Allosteric competitive inhibitors of the glucose-1-phosphate thymidylyltransferase (RmlA) from Pseudomonas aeruginosa

Glucose-1-phosphate thymidylyltransferase (RmlA) catalyzes the condensation of glucose-1-phosphate (G1P) with deoxy-thymidine triphosphate (dTTP) to yield dTDP-d-glucose and pyrophosphate. This is the first step in the l-rhamnose biosynthetic pathway. l-Rhamnose is an important component of the cell wall of many microorganisms, including Mycobacterium tuberculosis and Pseudomonas aeruginosa. Here we describe the first nanomolar inhibitors of P. aeruginosa RmlA. These thymine analogues were identified by high-throughput screening and subsequently optimized by a combination of protein crystallography, in silico screening, and synthetic chemistry. Some of the inhibitors show inhibitory activity against M. tuberculosis. The inhibitors do not bind at the active site of RmlA but bind at a second site remote from the active site. Despite this, the compounds act as competitive inhibitors of G1P but with high cooperativity. This novel behavior was probed by structural analysis, which suggests that the inhibitors work by preventing RmlA from undergoing the conformational change key to its ordered bi-bi mechanism.

Divergent functions of the myotubularin (MTM) homologs AtMTM1 and AtMTM2 in Arabidopsis thaliana: evolution of the plant MTM family

Myotubularin and myotubularin-related proteins are evolutionarily conserved in eukaryotes. Defects in their function result in muscular dystrophy, neuronal diseases and leukemia in humans. In contrast to the animal lineage, where genes encoding both active and inactive myotubularins (phosphoinositide 3-phosphatases) have appeared and proliferated in the basal metazoan group, myotubularin genes are not found in the unicellular relatives of green plants. However, they are present in land plants encoding proteins highly similar to the active metazoan enzymes. Despite their remarkable structural conservation, plant and animal myotubularins have significantly diverged in their functions. While loss of myotubularin function causes severe disease phenotypes in humans it is not essential for the cellular homeostasis under normal conditions in Arabidopsis thaliana. Instead, myotubularin deficiency is associated with altered tolerance to dehydration stress. The two Arabidopsis genes AtMTM1 and AtMTM2 have originated from a segmental chromosomal duplication and encode catalytically active enzymes. However, only AtMTM1 is involved in elevating the cellular level of phosphatidylinositol 5-phosphate in response to dehydration stress, and the two myotubularins differentially affect the Arabidopsis dehydration stress-responding transcriptome. AtMTM1 and AtMTM2 display different localization patterns in the cell, consistent with the idea that they associate with different membranes to perform specific functions. A single amino acid mutation in AtMTM2 (L250W) results in a dramatic loss of subcellular localization. Mutations in this region are linked to disease conditions in humans.

Indole-3-glycerol-phosphate synthase is recognized by a cold-inducible group II chaperonin in Thermococcus kodakarensis

Thermococcus kodakarensis optimally grows at 85°C and possesses two chaperonins, cold-inducible CpkA and heat-inducible CpkB. Gene disruptants DA1 (ΔcpkA) and DB1 (ΔcpkB) showed decreased cell growth at 60°C and 93°C, respectively. The DB2 mutant (ΔcpkAcpkB ΔcpkB), whose cpkB gene was expressed under the control of the cpkA promoter, did not grow at 60°C, and the DB3 mutant [ΔcpkA(1-524)cpkB(1-524) ΔcpkB], whose CpkA amino acid residues 1 to 524 were replaced with corresponding CpkB residues that maintained the C-terminal region intact, grew at 60°C, implying that the CpkA C-terminal region plays a key role in cell growth at 60°C. To screen for specific CpkA target proteins, comparative pulldown studies with anti-Cpk were performed using cytoplasmic fractions from DA1 cells cultivated at 93°C and DB1 cells cultivated at 60°C. Among the proteins coprecipitated with anti-Cpk, TK0252, encoding indole-3-glycerol-phosphate synthase (TrpC), showed the highest Mascot score. Counter-pulldown experiments were also performed on DA1 and DB1 extracts using anti-TrpC. CpkA coimmunoprecipitated with anti-TrpC while CpkB did not. The results obtained indicate that TrpC is a specific target for CpkA. The effects of Cpks on denatured TrpC were then examined. The refolding of partially denatured TrpC was accelerated by the addition of CpkA but not by adding CpkB. DA1 cells grew optimally in minimal medium only in the presence of tryptophan but hardly grew in the absence of tryptophan at 60°C. It has been suggested that a lesion of functional TrpC is caused by cpkA disruption, resulting in tryptophan auxotrophy.

Cooperative assembly and dynamic disassembly of MDA5 filaments for viral dsRNA recognition

MDA5, an RIG-I-like helicase, is a conserved cytoplasmic viral RNA sensor, which recognizes dsRNA from a wide-range of viruses in a length-dependent manner. It has been proposed that MDA5 forms higher-order structures upon viral dsRNA recognition or during antiviral signaling, however the organization and nature of this proposed oligomeric state is unknown. We report here that MDA5 cooperatively assembles into a filamentous oligomer composed of a repeating segmental arrangement of MDA5 dimers along the length of dsRNA. Binding of MDA5 to dsRNA stimulates its ATP hydrolysis activity with little coordination between neighboring molecules within a filament. Individual ATP hydrolysis in turn renders an intrinsic kinetic instability to the MDA5 filament, triggering dissociation of MDA5 from dsRNA at a rate inversely proportional to the filament length. These results suggest a previously unrecognized role of ATP hydrolysis in control of filament assembly and disassembly processes, thereby autoregulating the interaction of MDA5 with dsRNA, and provides a potential basis for dsRNA length-dependent antiviral signaling.

Phosphatidylinositol 5-phosphate links dehydration stress to the activity of ARABIDOPSIS TRITHORAX-LIKE factor ATX1

Background

Changes in gene expression enable organisms to respond to environmental stress. Levels of cellular lipid second messengers, such as the phosphoinositide PtdIns5P, change in response to a variety of stresses and can modulate the localization, conformation and activity of a number of intracellular proteins. The plant trithorax factor (ATX1) tri-methylates the lysine 4 residue of histone H3 (H3K4me3) at gene coding sequences, which positively correlates with gene transcription. Microarray analysis has identified a target gene (WRKY70) that is regulated by both ATX1 and by the exogenous addition of PtdIns5P in Arabidopsis. Interestingly, ATX1 contains a PtdIns5P interaction domain (PHD finger) and thus, phosphoinositide signaling, may link environmental stress to changes in gene transcription.

Principal Findings

Using the plant Arabidopsis as a model system, we demonstrate a link between PtdIns5P and the activity of the chromatin modifier ATX1 in response to dehydration stress. We show for the first time that dehydration leads to an increase in cellular PtdIns5P in Arabidopsis. The Arabidopsis homolog of myotubularin (AtMTM1) is capable of generating PtdIns5P and here, we show that AtMTM1 is essential for the induced increase in PtdIns5P upon dehydration. Furthermore, we demonstrate that the ATX1-dependent gene, WRKY70, is downregulated during dehydration and that lowered transcript levels are accompanied by a drastic reduction in H3K4me3 of its nucleosomes. We follow changes in WRKY70 nucleosomal K4 methylation as a model to study ATX1 activity at chromatin during dehydration stress. We found that during dehydration stress, the physical presence of ATX1 at the WRKY70 locus was diminished and that ATX1 depletion resulted from it being retained in the cytoplasm when PtdIns5P was elevated. The PHD of ATX1 and catalytically active AtMTM1 are required for the cytoplasmic localization of ATX1.

Conclusions/Significance

The novelty of the manuscript is in the discovery of a mechanistic link between a chromatin modifying activity (ATX1) and a lipid (PtdIns5P) synthesis in a signaling pathway that ultimately results in altered expression of ATX1 dependent genes downregulated in response to dehydration stress.

The Arabidopsis chromatin modifier ATX1, the myotubularin-like AtMTM and the response to drought

Plants respond to environmental stresses by altering transcription of genes involved in the response. The chromatin modifier ATX1 regulates expression of a large number of genes; consequently, factors that affect ATX1 activity would also influence expression from ATX1-regulated genes. Here, we demonstrate that dehydration is such a factor implicating ATX1 in the plant's response to drought. In addition, we report that a hitherto unknown Arabidopsis gene, At3g10550, encodes a phosphoinositide 3'-phosphatase related to the animal myotubularins (AtMTM1). Myotubularin activities in plants have not been described and herein, we identify an overlapping set of genes co-regulated by ATX1 and AtMTM under drought conditions. We propose that these shared genes represent the ultimate targets of partially overlapping branches of the pathways of the nuclear ATX1 and the cytoplasmic AtMTM1. Our analyses offer first genome-wide insights into the relationship of an epigenetic factor and a lipid phosphatase from the other end of a shared drought responding pathway in Arabidopsis.

Calcineurin inhibition in splenocytes induced by pavlovian conditioning

Pavlovian conditioning is one of the major neurobiological mechanisms of placebo effects, potentially influencing the course of specific diseases and the response to a pharmacological therapy, such as immunosuppression. In our study with behaviorally conditioned rats, a relevant taste (0.2% saccharin) preceded the application of the immunosuppressive drug cyclosporin A (CsA), a specific calcineurin (CaN) inhibitor. Our results demonstrate that through pavlovian conditioning the particular pharmacological properties of CsA can be transferred to a neutral taste, i.e., CaN activity was inhibited in splenocytes from conditioned rats after reexposure to the gustatory stimulus. Concomitant immune consequences were observed on ex vivo mitogenic challenge (anti-CD3). Particularly, Th1-cytokine, but not Th2-cytokine, production and cell proliferation were impeded. Appropriate pharmacological and behavioral controls certify that all these changes in T-lymphocyte reactivity are attributable to mere taste reexposure. Furthermore, the underlying sympathetic-lymphocyte interaction was revealed modeling the conditioned response in vitro. CaN activity in CD4(+) T lymphocytes is reduced by beta-adrenergic stimulation (terbutaline), with these effects antagonized by the beta-adrenoreceptor antagonist nadolol. In summary, CaN was identified as the intracellular target for inducing conditioned immunosuppression by CsA, contributing to our understanding of the intracellular mechanisms behind "learned placebo effects."

Synthesis of 3,5-difluorotyrosine-containing peptides: application in substrate profiling of protein tyrosine phosphatases

Fully protected 3,5-difluorotyrosine (F2Y), Fmoc-F2Y(tBu)-OH, is efficiently prepared by a chemoenzymatic process and incorporated into individual peptides and combinatorial peptide libraries. The F2Y-containing peptides display kinetic properties toward protein tyrosine phosphatases (PTPs) similar to their corresponding tyrosine-containing counterparts but are resistant to tyrosinase action. These properties make F2Y a useful tyrosine surrogate during peptide library screening for optimal PTP substrates.

A High-Throughput Microfluidic Assay for SH2 Domain-Containing Inositol 5-Phosphatase 2

SH2 domain-containing inositol 5-phosphatase 2 (SHIP2) is a potential drug target for the treatment of type 2 diabetes. This enzyme serves as a negative regulator of insulin-mediated signal transduction by catalyzing the dephosphorylation of the second messenger lipid molecule phosphatidylinositol 3,4,5-triphosphate. Traditionally, assays for phosphoinositide phosphatases such as SHIP2 have relied on radiolabeled phosphatidylinositol-containing lipid membranes and chromatographic separation of labeled phospholipid substrate from product by thin-layer chromatography. We have expressed and purified catalytically active phosphatase domain constructs of SHIP2 from Escherichia coli and developed a sensitive and antibody- or binding protein-independent assay for SHIP2 amenable to high-throughput screening of phosphoinositide phosphatases or phosphoinositide kinases. This microfluidic assay, with Z' values approximately 0.8, is based upon the difference in mobility within an electric field between a fluorophore-labeled phosphatidylinositol 3,4,5-triphosphate substrate and the corresponding 3,4-bisphosphate product. High-throughput screening of a 91,060-member compound library in 384-well format resulted in the identification of SHIP2 inhibitors.

Activation of calcineurin in human failing heart ventricle by endothelin-1, angiotensin II and urotensin II

1 The calcineurin (CaN) enzyme-transcriptional pathway is critically involved in hypertrophy of heart muscle in some animal models. Currently there is no information concerning the regulation of CaN activation by endogenous agonists in human heart. 2 Human right ventricular trabeculae from explanted human (14 male/2 female) failing hearts were set up in a tissue bath and electrically paced at 1 Hz and incubated with or without 100 nM endothelin-1 (ET-1), 10 M, angiotensin-II (Ang II) or 20 nM human urotensin-II (hUII) for 30 min. Tissues from four patients were incubated with 200 nM tacrolimus (FK506) for 30 min and then incubated in the presence or absence of ET-1 for a further 30 min. 3 ET-1 increased contractile force in all 13 patients (P<0.001). Ang II and hUII increased contractile force in three out of eight and four out of 10 patients but overall nonsignificantly (P>0.1). FK506 had no effect on contractile force (P=0.12). 4 ET-1, Ang II and hUII increased calcineurin activity by 32, 71 and 15%, respectively, while FK506 reduced activity by 34%. ET-1 in the presence of FK506 did not restore calcineurin activity (P=0.1). 5 There was no relationship between basal CaN activity and expression levels in the right ventricle. Increased levels of free phosphate were detected in ventricular homogenates that were incubated with PKC(epsilon) compared to samples incubated without PKC(epsilon). 6 Endogenous cardiostimulants which activate G(alpha)q-coupled receptors increase the activity of calcineurin in human heart following acute (30 min) exposure. PKC may contribute to this effect by increasing levels of phosphorylated calcineurin substrate.

Chemical Confirmation of a Pentavalent Phosphorane in Complex with β-Phosphoglucomutase

This communication reports the X-ray crystal structure of the alpha-d-galactose-1-phosphate complex with that of Lactococcus lactis beta-phosphoglucomutase (beta-PGM) crystallized in the presence of Mg2+ cofactor and the enzyme-to-phosphorus ratio determined by protein and phosphate analyses of the crystalline complex. The 1:1 ratio determined for this complex was compared to the 1:2 ratio determined for the crystals of beta-PGM grown in the presence of substrate and Mg2+ cofactor. This result verifies the published structure assignment of this latter complex as the phosphorane adduct formed by covalent bonding between the active site Asp8 carboxylate to the C(1)phosphorus of the beta-glucose 1,6-bisphosphate ligand and rules out the proposal of a beta-PGM-glucose-6-phosphate-1-MgF3- complex.

(?)-Clausenamide potentiates synaptic transmission in the dentate gyrus of rats

The effect of clausenamide on synaptic transmission in the dentate gyrus of rats in vivo and its possible mechanism of action were investigated in this study. Four of 16 enantiomers showed potentiating effects on basal synaptic transmission in anesthetized animals. By comparing one pair of enantiomers, (-)-clausenamide and (+)-clausenamide, we can report three primary findings: (1) (-)-clausenamide potentiated synaptic transmission in both anesthetized and freely moving animals while (+)-clausenamide showed no or little effect; (2) (-)-clausenamide increased the magnitude of long-term potentiation (LTP) induced by high-frequency stimulation (HFS) in anesthetized animals whereas (+)-clausenamide had no effect; (3) voltage-dependent calcium channels (VDCCs) calcineurin and calpain are involved in (-)-clausenamide-induced potentiation of synaptic transmission. Because hippocampal LTP is thought to reflect a cellular mechanism involved in learning and memory, our findings may provide the pharmacological basis for understanding the nootropic mechanisms of (-)-clausenamide, which is the first chiral nootropic agent developed in China.

Cyclosporin A inhibits calcineurin (phosphatase 2B) and P-glycoprotein activity in Entamoeba histolytica

Cyclosporin A (CsA) inhibits the proliferation of several protozoan parasites through blocking the activity of calcineurin (Cn) or P-glycoproteins (Pgp). We report here, that inhibition of the proliferation of Entamoeba histolytica trophozoites, the causal agent of human amebiasis, is due to interference of the phosphatase activity of Cn, in a similar fashion to the effect of this immunosuppressive drug on T lymphocytes. The non-immunosuppressive CsA analog PSC-833, which binds Pgp without interfering the function of Cn, did not inhibit the proliferation of HM1:IMSS trophozoites. Moreover, phosphatase activity of amebic Cn, detected using the phosphopeptide RII, was drastically affected by incubation with CsA, but not with PSC-833. On the other hand, both drugs were also tested on clone C2 trophozoites, which grow in the presence of emetine due to over-expression of Pgp. The effect of CsA was similar to that observed on HM1:IMSS trophozoites, whereas PSC-833 only affected the proliferation and viability of clone C2 when the trophozoites were grown in the presence of 40 microM of emetine, suggesting an interference of the Pgp activity. This suggestion was confirmed by results from experiments of Pgp-dependent effux of rhodamine from pre-loaded trophozoites, in the presence of either of these drugs. Therefore, CsA inhibition of E. histolytica trophozoite proliferation is more likely due to Cn than Pgp activity inhibition.