Calcium-dependent Protein Kinase 1 Research Articles

Isatin-1,2,3-triazole derivatives: synthesis, molecular docking and evaluation against acute experimental toxoplasmosis

Toxoplasmosis remains a challenge for both public health and animal husbandry which created a constant demand to develop novel compounds using innovative methods. To join this relentless quest for an ideal chemotherapeutic agent, herein, we developed newly synthesized isatin-1,2,3-triazole derivatives. Three compounds (5a, 5b and 5c) were synthesized, characterized, and loaded on chitosan nanoparticles (CNPs) and then evaluated accordingly. Initially, a molecular docking study was carried out which revealed the effective interaction with the target enzymes; purine nucleoside phosphorylase (PNPase) and T. gondii calcium-dependent protein kinase-1 (TgCDPK1). This was further substantiated by in vivo evaluation of the three compounds (5a-c) and their nanoformulae (5a-CNPs, 5b-CNPs, and 5c-CNPs) against acute Toxoplasma gondii infection in murine model. It is worthy of note that all tested compounds and their nanoformulae produced a significant reduction of parasite burden in both peritoneal fluid and liver impression smear and profound ultrastructural alterations, detected by scanning electron microscopy, compared to the infected non-treated control. The nanoformula 5c-CNPs yielded the most outstanding results with the highest tachyzoite reduction percentage in both peritoneal fluid (98.1%) and liver impression smear (95.3%). Furthermore, the serum levels of liver enzymes (aspartate transaminase (AST) and alanine transaminase (ALT), and renal function tests (urea and creatinine) in mice were within normal limits which makes them more appealing candidates with proven safety. To the best of our knowledge, the present work is the first in silico and in vivo study proving the anti-Toxoplasma effect of isatin-1,2,3- triazoles which paves the way for further development of isatin and triazole-based leads for the treatment of toxoplasmosis.

Efficacy of the bumped kinase inhibitor BKI-1708 against the cyst-forming apicomplexan parasites Toxoplasma gondii and Neospora caninum in vitro and in experimentally infected mice

Toxoplasma gondii and Neospora caninum are major worldwide morbidity-causing pathogens. Bumped kinase inhibitors (BKIs) are a compound class that has been optimized to target the apicomplexan calcium-dependent protein kinase 1 (CDPK1) – and several members of this class have proven to be safe and highly active in vitro and in vivo. BKI-1708 is based on a 5-aminopyrazole-4-carboxamide scaffold, and exhibited in vitro IC50 values of 120 nM for T. gondii and 480 nM for N. caninum β-galactosidase expressing strains, and did not affect human foreskin fibroblast (HFF) viability at concentrations up to 25 μM. Electron microscopy established that exposure of tachyzoite-infected fibroblasts to 2.5 μM BKI-1708 in vitro induced the formation of multinucleated schizont-like complexes (MNCs), characterized by continued nuclear division and harboring newly formed intracellular zoites that lack the outer plasma membrane. These zoites were unable to finalize cytokinesis to form infective tachyzoites. BKI-1708 did not affect zebrafish (Danio rerio) embryo development during the first 96 h following egg hatching at concentrations up to 2 μM. Treatments of mice with BKI-1708 at 20 mg/kg/day during five consecutive days resulted in drug plasma levels ranging from 0.14 to 4.95 μM. In vivo efficacy of BKI-1708 was evaluated by oral application of 20 mg/kg/day from day 9–13 of pregnancy in mice experimentally infected with N. caninum (NcSpain-7) tachyzoites or T. gondii (TgShSp1) oocysts. This resulted in significantly decreased cerebral parasite loads and reduced vertical transmission in both models without drug-induced pregnancy interference.

Pyridopyrimidinones as a new chemotype of calcium dependent protein kinase 1 (CDPK1) inhibitors for Cryptosporidium

The protozoan protein kinase calcium-dependent protein kinase 1 (CDPK1) has emerged as a potential therapeutic target for the treatment of cryptosporidiosis. A focused screen of known kinase inhibitors identified a pyridopyrimidinone as a new chemotype of Cryptosporidium parvum (Cp) CDPK1 inhibitors. Structural comparison of CpCDPK1 to two representative human kinases, RIPK2 and Src, revealed differences in the positioning of the αC-helix that was used in the design of a potent pyridopyrimidinone-based CpCDPK1 inhibitor 7 (a.k.a. UH15–16, IC50 = 10 nM), which blocked the growth of three C. parvum strains (EC50 = 12–40 nM) as well as C. hominis (EC50 = 85 nM) in HCT-8 host cells. Pharmacokinetic and tissue distribution analyses indicated that 7 had low systemic exposure after oral administration, but high gastrointestinal concentration, as well as good Caco-2 cell permeability. Finally, 7 demonstrated partial efficacy in an IL-12 knock-out mouse model of acute cryptosporidiosis.

Characterization of putative calcium-dependent protein kinase-1 (TaCPK-1) gene: hubs in signalling and tolerance network of wheat under terminal heat.

The online version contains supplementary material available at 10.1007/s13205-024-03989-6.

An Early Treatment With BKI-1748 Exhibits Full Protection Against Abortion and Congenital Infection in Sheep Experimentally Infected With Toxoplasma gondii.

Congenital toxoplasmosis in humans and in other mammalian species, such as small ruminants, is a well-known cause of abortion and fetal malformations. The calcium-dependent protein kinase 1 (CDPK1) inhibitor BKI-1748 has shown a promising safety profile for its use in humans and a good efficacy against Toxoplasma gondii infection in vitro and in mouse models. Ten doses of BKI-1748 given every other day orally in sheep at 15 mg/kg did not show systemic or pregnancy-related toxicity. In sheep experimentally infected at 90 days of pregnancy with 1000 TgShSp1 oocysts, the BKI-1748 treatment administered from 48 hours after infection led to complete protection against abortion and congenital infection. In addition, compared to infected/untreated sheep, treated sheep showed a drastically lower rectal temperature increase and none showed IgG seroconversion throughout the study. In conclusion, BKI-1748 treatment in pregnant sheep starting at 48 hours after infection was fully effective against congenital toxoplasmosis.

Amodiaquine drug pressure selects nonsynonymous mutations in pantothenate kinase 1, diacylglycerol kinase, and phosphatidylinositol-4 kinase in Plasmodium berghei ANKA

Background Lumefantrine (LM), piperaquine (PQ), and amodiaquine (AQ), the long-acting components of the artemisinin-based combination therapies (ACTs), are a cornerstone of malaria treatment in Africa. Studies have shown that PQ, AQ, and LM resistance may arise independently of predicted modes of action. Protein kinases have emerged as mediators of drug action and efficacy in malaria parasites; however, the link between top druggable Plasmodium kinases with LM, PQ, and AQ resistance remains unclear. Using LM, PQ, or AQ-resistant Plasmodium berghei parasites, we have evaluated the association of choline kinase (CK), pantothenate kinase 1 (PANK1), diacylglycerol kinase (DAGK), and phosphatidylinositol-4 kinase (PI4Kβ), and calcium-dependent protein kinase 1 (CDPK1) with LM, PQ, and AQ resistance in Plasmodium berghei ANKA. Methods We used in silico bioinformatics tools to identify ligand-binding motifs, active sites, and sequence conservation across the different parasites. We then used PCR and sequencing analysis to probe for single nucleotide polymorphisms (SNPs) within the predicted functional motifs in the CK, PANK1, DAGK, PI4Kβ, and CDPK1. Using qPCR analysis, we measured the mRNA amount of PANK1, DAGK, and PI4Kβ at trophozoites and schizonts stages. Results We reveal sequence conservation and unique ligand-binding motifs in the CK, PANK1, DAGK, PI4Kβ, and CDPK1 across malaria species. DAGK, PANK1, and PI4Kβ possessed nonsynonymous mutations; surprisingly, the mutations only occurred in the AQr parasites. PANK1 acquired Asn394His, while DAGK contained K270R and K292R mutations. PI4Kβ had Asp366Asn, Ser1367Arg, Tyr1394Asn and Asp1423Asn. We show downregulation of PANK1, DAGK, and PI4Kβ in the trophozoites but upregulation at the schizonts stages in the AQr parasites. Conclusions The selective acquisition of the mutations and the differential gene expression in AQ-resistant parasites may signify proteins under AQ pressure. The role of the mutations in the resistant parasites and their impact on drug responses require investigations using reverse genetics techniques in malaria parasites.

Photoswitchable Inhibitors to Optically Control Specific Kinase Activity.

Potent and selective small-molecule inhibitors are valuable tools to elucidate the functions of protein kinases within complex signaling networks. Incorporation of a photoswitchable moiety into the inhibitor scaffold offers the opportunity to steer inhibitor potency with temporal precision, while the challenge of selective inhibition can often be addressed by employing a chemical genetic approach, termed the analog-sensitive method. Here, we combine the perks of these two approaches and report photoswitchable azopyrazoles to target calcium-dependent protein kinase 1 (CDPK1) from Toxoplasma gondii, a kinase naturally susceptible to analog-sensitive kinase inhibitors due to its glycine gatekeeper residue. The most promising azopyrazoles display favorable photochemical properties, thermal stability, and a substantial difference in IC50 values between both photostationary states. Consequently, the CDPK1 kinase reaction can be controlled dynamically and reversibly by applying light of different wavelengths. Inhibition of CDPK1 by the azopyrazoles drastically relies on the nature of the gatekeeper residue as a successive increase in gatekeeper size causes a concurrent loss of inhibitory activity. Furthermore, two photoswitchable inhibitors exhibit activity against T. gondii and Cryptosporidium parvum infection in a cell culture model, making them a promising addition to the toolbox for dissecting the role of CDPK1 in the infectious cycle with high temporal control. Overall, this work merges the benefits of the analog-sensitive approach and photopharmacology without compromising inhibitory potency and thus holds great promise for application to other protein kinases in the future.

Amodiaquine drug pressure selects nonsynonymous mutations in pantothenate kinase 1, diacylglycerol kinase, and phosphatidylinositol-4 kinase in Plasmodium berghei ANKA

Background: Lumefantrine (LM), piperaquine (PQ), and amodiaquine (AQ), the long-acting components of the artemisinin-based combination therapies (ACTs), are a cornerstone of malaria treatment in Africa. Studies have shown that PQ, AQ, and LM resistance may arise independently of predicted modes of action. Protein kinases have emerged as mediators of drug action and efficacy in malaria parasites; however, the link between top druggable Plasmodium kinases with LM, PQ, and AQ resistance remains unclear. Using LM, PQ, or AQ-resistant Plasmodium berghei parasites, we have evaluated the association of choline kinase (CK), pantothenate kinase 1 (PANK1), diacylglycerol kinase (DAGK), and phosphatidylinositol-4 kinase (PI4Kβ), and calcium-dependent protein kinase 1 (CDPK1) with LM, PQ, and AQ resistance in Plasmodium berghei ANKA. Methods: We used in silico bioinformatics tools to identify ligand-binding motifs, active sites, and sequence conservation across the different parasites. We then used PCR and sequencing analysis to probe for single nucleotide polymorphisms (SNPs) within the predicted functional motifs in the CK, PANK1, DAGK, PI4Kβ, and CDPK1. Using qPCR analysis, we finally measured the mRNA amount of PANK1, DAGK, and PI4Kβ at trophozoites and schizonts stages. Results: We reveal sequence conservation and unique ligand-binding motifs in the CK, PANK1, DAGK, PI4Kβ, and CDPK1 across malaria species. DAGK, PANK1, and PI4Kβ possessed nonsynonymous mutations; surprisingly, the mutations only occurred in the AQr parasites. PANK1 acquired Asn394His, while DAGK contained K270R and K292R mutations. PI4Kβ had Asp366Asn, Ser1367Arg, Tyr1394Asn and Asp1423Asn. We show downregulation of PANK1, DAGK, and PI4Kβ in the trophozoites but upregulation at the schizonts stages in the AQr parasites. Conclusions: The selective acquisition of the mutations and the differential gene expression in AQ-resistant parasites may signify proteins under AQ pressure. The role of the mutations in the resistant parasites and the impact on drug responses require further investigations in malaria parasites.

Amodiaquine drug pressure selects nonsynonymous mutations in pantothenate kinase 1, diacylglycerol kinase, and phosphatidylinositol-4 kinase in Plasmodium berghei ANKA.

Lumefantrine (LM), piperaquine (PQ), and amodiaquine (AQ), the long-acting components of the artemisinin-based combination therapies (ACTs), are a cornerstone of malaria treatment in Africa. Studies have shown that PQ, AQ, and LM resistance may arise independently of predicted modes of action. Protein kinases have emerged as mediators of drug action and efficacy in malaria parasites; however, the link between top druggable Plasmodium kinases with LM, PQ, and AQ resistance remains unclear. Using LM, PQ, or AQ-resistant Plasmodium berghei parasites, we have evaluated the association of choline kinase (CK), pantothenate kinase 1 (PANK1), diacylglycerol kinase (DAGK), and phosphatidylinositol-4 kinase (PI4Kβ), and calcium-dependent protein kinase 1 (CDPK1) with LM, PQ, and AQ resistance in Plasmodium berghei ANKA. We used in silico bioinformatics tools to identify ligand-binding motifs, active sites, and sequence conservation across the different parasites. We then used PCR and sequencing analysis to probe for single nucleotide polymorphisms (SNPs) within the predicted functional motifs in the CK, PANK1, DAGK, PI4Kβ, and CDPK1. Using qPCR analysis, we measured the mRNA amount of PANK1, DAGK, and PI4Kβ at trophozoites and schizonts stages. We reveal sequence conservation and unique ligand-binding motifs in the CK, PANK1, DAGK, PI4Kβ, and CDPK1 across malaria species. DAGK, PANK1, and PI4Kβ possessed nonsynonymous mutations; surprisingly, the mutations only occurred in the AQr parasites. PANK1 acquired Asn394His, while DAGK contained K270R and K292R mutations. PI4Kβ had Asp366Asn, Ser1367Arg, Tyr1394Asn and Asp1423Asn. We show downregulation of PANK1, DAGK, and PI4Kβ in the trophozoites but upregulation at the schizonts stages in the AQr parasites. The selective acquisition of the mutations and the differential gene expression in AQ-resistant parasites may signify proteins under AQ pressure. The role of the mutations in the resistant parasites and their impact on drug responses require investigations using reverse genetics techniques in malaria parasites.

Allosteric regulation of the inactive to active state conformational transition in CDPK1 protein of Plasmodium falciparum

The aim of the current study is to investigate the role of the CAD domain in the activation mechanism of calcium dependent protein kinase-1 of Plasmodium falciparum (PfCDPK1) and explore the possibility of allosteric inhibition of this kinase. PfCDPK1 belongs to CDPK family of apicomplexan kinases which have a C-terminal CAD domain. Microsecond scale MD simulations were performed on modeled structures of complete PfCDPK1 and its kinase domain alone. The simulations revealed that in absence of CAD the salt bridge between Glu116 in αC-helix and Lys85 in β3-sheet of kinase breaks after 200 ns resulting in inactive conformation of the kinase, but the salt bridge stays intact in the complete protein stabilizing it in active conformation. These results highlight the novel CAD mediated allosteric stabilization of the crucial salt bridge which is a hallmark of active conformation of kinase domains. The mechanistic details of the allosteric activation revealed by our study, opens up the possibility for design of allosteric inhibitors of PfCDPK1 kinase by disrupting the kinase:CAD interactions. Using a combination of machine learning and structure-based in silico screening, we have identified novel PPI modulators for allosteric inactivation of PfCDPK1 kinase.

Endochin-like quinolones (ELQs) and bumped kinase inhibitors (BKIs): Synergistic and additive effects of combined treatments against Neospora caninum infection in vitro and in vivo

The apicomplexan parasite Neospora caninum is an important causative agent of congenital neosporosis, resulting in abortion, birth of weak offspring and neuromuscular disorders in cattle, sheep, and many other species. Among several compound classes that are currently being developed, two have been reported to limit the effects of congenital neosporosis: (i) bumped kinase inhibitors (BKIs) target calcium dependent protein kinase 1 (CDPK1), an enzyme that is encoded by an apicoplast-derived gene and found only in apicomplexans and plants. CDPK1 is essential for host cell invasion and egress; (ii) endochin-like quinolones (ELQs) are inhibitors of the cytochrome bc1 complex of the mitochondrial electron transport chain and thus inhibit oxidative phosphorylation. We here report on the in vitro and in vivo activities of BKI-1748, and of ELQ-316 and its respective prodrugs ELQ-334 and ELQ-422, applied either as single-compounds or ELQ-BKI-combinations. In vitro, BKI-1748 and ELQ-316, as well as BKI-1748 and ELQ-334, acted synergistically, while this was not observed for the BKI-1748/ELQ-422 combination treatment. In a N. caninum-infected pregnant BALB/c mouse model, the synergistic effects observed in vitro were not entirely reproduced, but 100% postnatal survival and 100% inhibition of vertical transmission was noted in the group treated with the BKI-1748/ELQ-334 combination. In addition, the combined drug applications resulted in lower neonatal mortality compared to treatments with single drugs.

CAMP-Dependent Signaling Pathways as Potential Targets for Inhibition of Plasmodium falciparum Blood Stages.

We review the role of signaling pathways in regulation of the key processes of merozoite egress and red blood cell invasion by Plasmodium falciparum and, in particular, the importance of the second messengers, cAMP and Ca2+, and cyclic nucleotide dependent kinases. cAMP-dependent protein kinase (PKA) is comprised of cAMP-binding regulatory, and catalytic subunits. The less well conserved cAMP-binding pockets should make cAMP analogs attractive drug leads, but this approach is compromised by the poor membrane permeability of cyclic nucleotides. We discuss how the conserved nature of ATP-binding pockets makes ATP analogs inherently prone to off-target effects and how ATP analogs and genetic manipulation can be useful research tools to examine this. We suggest that targeting PKA interaction partners as well as substrates, or developing inhibitors based on PKA interaction sites or phosphorylation sites in PKA substrates, may provide viable alternative approaches for the development of anti-malarial drugs. Proximity of PKA to a substrate is necessary for substrate phosphorylation, but the P. falciparum genome encodes few recognizable A-kinase anchor proteins (AKAPs), suggesting the importance of PKA-regulatory subunit myristylation and membrane association in determining substrate preference. We also discuss how Pf14-3-3 assembles a phosphorylation-dependent signaling complex that includes PKA and calcium dependent protein kinase 1 (CDPK1) and how this complex may be critical for merozoite invasion, and a target to block parasite growth. We compare altered phosphorylation levels in intracellular and egressed merozoites to identify potential PKA substrates. Finally, as host PKA may have a critical role in supporting intracellular parasite development, we discuss its role at other stages of the life cycle, as well as in other apicomplexan infections. Throughout our review we propose possible new directions for the therapeutic exploitation of cAMP-PKA-signaling in malaria and other diseases caused by apicomplexan parasites.

In vitro activity, safety and in vivo efficacy of the novel bumped kinase inhibitor BKI-1748 in non-pregnant and pregnant mice experimentally infected with Neospora caninum tachyzoites and Toxoplasma gondii oocysts

Bumped kinase inhibitors (BKIs) target the apicomplexan calcium-dependent protein kinase 1 (CDPK1). BKI-1748, a 5-aminopyrazole-4-carboxamide compound when added to fibroblast cells concomitantly to the time of infection, inhibited proliferation of apicomplexan parasites at EC50s of 165 nM (Neospora caninum) and 43 nM (Toxoplasma gondii). Immunofluorescence and electron microscopy showed that addition of 2.5 μM BKI-1748 to infected HFF monolayers transformed parasites into multinucleated schizont-like complexes (MNCs) containing newly formed zoites, which were unable to separate and form infective tachyzoites or undergo egress. In zebrafish (Danio rerio) embryo development assays, no embryonic impairment was detected within 96 h at BKI-1748 concentrations up to 10 μM. In pregnant mice, BKI-1748 applied at days 9–13 of pregnancy at a dose of 20 mg/kg/day was safe and no pregnancy interference was observed. The efficacy of BKI-1748 was assessed in standardized pregnant mouse models infected with N. caninum (NcSpain-7) tachyzoites or T. gondii (TgShSp1) oocysts. In both models, treatments resulted in increased pup survival and profound inhibition of vertical transmission. However, in dams and non-pregnant mice, BKI-1748 treatments resulted in significantly decreased cerebral parasite loads only in T. gondii infected mice. In the T. gondii-model, ocular infection was detected in 10 out of 12 adult mice of the control group, but only in 3 out of 12 mice in the BKI-1748-treated group. Thus, TgShSp1 oocyst infection is a suitable model to study both cerebral and ocular infection by T. gondii. BKI-1748 represents an interesting candidate for follow-up studies on neosporosis and toxoplasmosis in larger animal models.

Overlapping and distinct roles of CDPK family members in the pre-erythrocytic stages of the rodent malaria parasite, Plasmodium berghei.

Invasion of hepatocytes by Plasmodium sporozoites initiates the pre-erythrocytic step of a malaria infection. Subsequent development of the parasite within hepatocytes and exit from them is essential for starting the disease-causing erythrocytic cycle. Identification of signaling pathways that operate in pre-erythrocytic stages provides insight into a critical step of infection and potential targets for chemoprotection from malaria. We demonstrate that P. berghei homologs of Calcium Dependent Protein Kinase 1 (CDPK1), CDPK4 and CDPK5 play overlapping but distinct roles in sporozoite invasion and parasite egress from hepatocytes. All three kinases are expressed in sporozoites. All three are required for optimal motility of sporozoites and consequently their invasion of hepatocytes. Increased cGMP can compensate for the functional loss of CDPK1 and CDPK5 during sporozoite invasion but cannot overcome loss of CDPK4. CDPK1 and CDPK5 expression is downregulated after sporozoite invasion. CDPK5 reappears in a subset of late stage liver stages and is present in all merosomes. Chemical inhibition of CDPK4 and depletion of CDPK5 in liver stages implicate these kinases in the formation and/or release of merosomes from mature liver stages. Furthermore, depletion of CDPK5 in merosomes significantly delays initiation of the erythrocytic cycle without affecting infectivity of hepatic merozoites. These data suggest that CDPK5 may be required for the rupture of merosomes. Our work provides evidence that sporozoite invasion requires CDPK1 and CDPK5, and suggests that CDPK5 participates in the release of hepatic merozoites.

Reduced treatment frequencies with bumped kinase inhibitor 1369 are effective against porcine cystoisosporosis

Bumped kinase inhibitors (BKIs) are a new class of antiprotozoal drugs that target calcium-dependent protein kinase 1 (CDPK1) in various apicomplexan parasites. A multiple dose regimen of BKI 1369 has been shown to be highly effective against Cystoisospora suis (syn. Isospora suis), the causative agent of neonatal porcine coccidiosis. However, multiple dosing may not be widely applicable in the field. The present study aimed to determine the efficacy of reduced treatment frequencies with BKI 1369 against porcine cystoisosporosis in vitro and in vivo. Pre-incubation of sporozoites with BKI 1369 completely failed to inhibit the infection in vitro unless treatment was prolonged post-infection. Notably, a single treatment of infected cell cultures 2 days post-infection (dpi) resulted in a significant reduction of merozoite replication. In an experimental infection model, treatment of suckling piglets experimentally infected with C. suis 2 and 4 dpi with 20 mg BKI 1369/kg body weight completely suppressed oocyst excretion. A single treatment on the day of infection or 2 dpi suppressed oocyst excretion in 50% and 82% of the piglets and reduced the quantitative excretion in those that shed oocysts by 95.2% and 98.4%, respectively. Moreover, a significant increase in body weight gain and reduced number of diarrhea days were observed in BKI 1369 treated piglets compared to the control piglets, irrespective of time points and frequencies of treatment. Given that reduced treatment frequencies with BKI 1369 are comparable in efficacy to repeated applications without any adverse effects, this could be considered as a practical therapeutic alternative against porcine cystoisosporosis.

Identifying the Target of an Antiparasitic Compound in Toxoplasma Using Thermal Proteome Profiling.

Apicomplexan parasites include the causative agents of malaria and toxoplasmosis. Cell-based screens in Toxoplasma previously identified a chemical modulator of calcium signaling (ENH1) that blocked parasite egress from host cells and exhibited potent antiparasitic activity. To identify the targets of ENH1, we adapted thermal proteome profiling to Toxoplasma, which revealed calcium-dependent protein kinase 1 (CDPK1) as a target. We confirmed the inhibition of CDPK1 by ENH1 in vitro and in parasites by comparing alleles sensitive or resistant to ENH1. CDPK1 inhibition explained the block in egress; however, the effects of ENH1 on calcium homeostasis and parasite viability were CDPK1-independent, implicating additional targets. Thermal proteome profiling of lysates from parasites expressing the resistant allele of CDPK1 identified additional candidates associated with the mitochondria and the parasite pellicle-compartments that potentially function in calcium release and homeostasis. Our findings illustrate the promise of thermal profiling to identify druggable targets that modulate calcium signaling in apicomplexan parasites.

Molecular dynamics simulations and biochemical characterization of Pf14-3-3 and PfCDPK1 interaction towards its role in growth of human malaria parasite.

Scaffold proteins play pivotal role as modulators of cellular processes by operating as multipurpose conformation clamps. 14-3-3 proteins are gold-standard scaffold modules that recognize phosphoSer/Thr (pS/pT) containing conserved motifs, and confer conformational changes leading to modulation of functional parameters of their target proteins. Modulation in functional activity of kinases has been attributed to their interaction with 14-3-3 proteins. Herein, we have annotated and characterized PF3D7_0818200 as 14-3-3 isoform I in Plasmodium falciparum 3D7, and its interaction with one of the key kinases of the parasite, Calcium-Dependent Protein Kinase 1 (CDPK1) by performing various analytical biochemistry and biophysical assays. Molecular dynamics simulation studies indicated that CDPK1 polypeptide sequence (61KLGpS64) behaves as canonical Mode I-type (RXXpS/pT) consensus 14-3-3 binding motif, mediating the interaction. The 14-3-3I/CDPK1 interaction was validated in vitro with ELISA and SPR, which confirmed that the interaction is phosphorylation dependent, with binding affinity constant of 670 ± 3.6 nM. The interaction of 14-3-3I with CDPK1 was validated with well characterized optimal 14-3-3 recognition motifs: Mode I-type ARSHpSYPA and Mode II-type RLYHpSLPA, by simulation studies and ITC. This interaction was found to marginally enhance CDPK1 functional activity. Furthermore, interaction antagonizing peptidomimetics showed growth inhibitory impact on the parasite indicating crucial physiological role of 14-3-3/CDPK1 interaction. Overall, this study characterizes 14-3-3I as a scaffold protein in the malaria parasite and unveils CDPK1 as its previously unidentified target. This sets a precedent for the rational design of 14-3-3 based PPI inhibitors by utilizing 14-3-3 recognition motif peptides, as a potential antimalarial strategy.

<i>In Silico</i> Study on Interaction and Preliminary Toxicity Prediction of <i>Eleutherine americana</i> Components as an Antifungal and Antitoxoplasmosis Candidate

Red bulbs of Eleutherine americana (Aubl.) Merr. ex K. Heyne has been known for its high content of naphthoquinones that have antifungal and antiparasitic activities. In this research, in silico interaction study was performed between 31 compounds reported to be found in E. americana with the selected target proteins for antifungal and antitoxoplasmosis activity using the molecular docking method. An ORPs (OSBP-related proteins), Osh4 (PDB ID: 1ZHX), and N-myristoyltransferase (Nmt, PDB ID: 1IYL) were used as the antifungal target proteins. Toxoplasma gondii purine nucleoside phosphorylase (TgPNP, PDB ID: 3MB8) and calcium-dependent protein kinase-1 (TgCDPK1, PDB ID: 4M84) were used as antitoxoplasmosis target proteins. Three-dimensional structures of the test compounds were made and optimized using GaussView 6.0 and Gaussian 09W. The target proteins were prepared using the Discovery Studio 2016 Program. Aquatic toxicity prediction as the preliminary assessment of the safety of the compounds was performed using ECOSAR v2.0. The results suggest that the compound having both the smallest free binding energy compared with positive control and other test compounds and low predicted toxicity is β-sitosterol with a free binding energy of ‒11.55 and ‒11.18 kcal/mol towards Osh4 and Nmt and ‒8.06 and ‒10.29 kcal/mol towards TgPNP and TgCDPK1, respectively.

Optimizing Pyrazolopyrimidine Inhibitors of Calcium Dependent Protein Kinase 1 for Treatment of Acute and Chronic Toxoplasmosis.

Calcium dependent protein kinase 1 (CDPK1) is an essential Ser/Thr kinase that controls invasion and egress by the protozoan parasite Toxoplasma gondii. The Gly gatekeeper of CDPK1 makes it exquisitely sensitive to inhibition by small molecule 1H-pyrazolo[3,4-d]pyrimidine-4-amine (PP) compounds that are bulky ATP mimetics. Here we rationally designed, synthesized, and tested a series of novel PP analogs that were evaluated for inhibition of CDPK1 enzyme activity in vitro and parasite growth in cell culture. Optimal substitution on the PP scaffold included 2-pyridyl ethers directed into the hydrophobic pocket and small carbocyclic rings accessing the ribose-binding pocket. Further optimization of the series led to identification of the lead compound 3a that displayed excellent potency, selectivity, safety profile, and efficacy in vivo. The results of these studies provide a foundation for further work to optimize CDPK1 inhibitors for the treatment of acute and chronic toxoplasmosis.

Calcium-Dependent Protein Kinase CPK1 Controls Cell Death by In Vivo Phosphorylation of Senescence Master Regulator ORE1.

Calcium-regulated protein kinases are key components of intracellular signaling in plants that mediate rapid stress-induced responses to changes in the environment. To identify in vivo phosphorylation substrates of CALCIUM-DEPENDENT PROTEIN KINASE1 (CPK1), we analyzed the conditional expression of constitutively active CPK1 in conjunction with in vivo phosphoproteomics. We identified Arabidopsis (Arabidopsis thaliana) ORESARA1 (ORE1), the developmental master regulator of senescence, as a direct CPK1 phosphorylation substrate. CPK1 phosphorylates ORE1 at a hotspot within an intrinsically disordered region. This augments transcriptional activation by ORE1 of its downstream target gene BIFUNCTIONAL NUCLEASE1 (BFN1). Plants that overexpress ORE1, but not an ORE1 variant lacking the CPK1 phosphorylation hotspot, promote early senescence. Furthermore, ORE1 is required for enhanced cell death induced by CPK1 signaling. Our data validate the use of conditional expression of an active enzyme combined with phosphoproteomics to decipher specific kinase target proteins of low abundance, of transient phosphorylation, or in yet-undescribed biological contexts. Here, we have identified that senescence is not just under molecular surveillance manifested by stringent gene regulatory control over ORE1 In addition, the decision to die is superimposed by an additional layer of control toward ORE1 via its posttranslational modification linked to the calcium-regulatory network through CPK1.