Subunit Of cAMP-dependent Protein Kinase Research Articles

Physico-chemical properties of two point mutants of small heat shock protein HspB6 (Hsp20) with abrogated cardioprotection

Physico-chemical properties of HspB6 S10F and P20L mutants with abrogated cardioprotective activity and associated with different forms of cardiomyopathy were analyzed. Under normal conditions both the wild-type HspB6 and its mutants formed small size oligomers (dimers) with apparent molecular weight of 50–60 kDa. Under crowding conditions (0.5 M trimethylamine N-oxide, TMAO) the wild-type HspB6 remained predominantly dimeric or formed small molecular weight complexes, whereas both mutants tended to form high molecular weight complexes. Catalytic subunit of cAMP-dependent protein kinase phosphorylated the wild-type HspB6 and its S10F mutant with comparable rate. The rate of P20L mutant phosphorylation was higher than that of the wild-type HspB6. S10F and P20L mutations did not affect interaction of phosphorylated HspB6 with universal adapter proteins 14-3-3. The wild-type HspB6 was resistant to heat-induced denaturation and aggregation, whereas both its mutants were denatured and started to aggregate at temperature much lower than its wild-type counterpart. Titration with fluorescent probe bis-ANS was accompanied by larger increase of fluorescence in the case of both mutants than in the case of the wild-type HspB6. Both mutants possessed higher chaperone-like activity than the wild-type protein. It is concluded that both S10F and P20L mutations are accompanied by increase of hydrophobicity of the very N-terminal region of HspB6 leading to increased aggregation at elevated temperature, formation of large complexes under crowding conditions and increased chaperone-like activity measured in vitro. Increased hydrophobicity and self-association can affect substrate specificity and interaction with certain target proteins thus leading to decrease or complete abrogation of cardioprotective activity.

Comprehensive Characterization of the Recombinant Catalytic Subunit of cAMP-Dependent Protein Kinase by Top-Down Mass Spectrometry.

Reversible phosphorylation plays critical roles in cell growth, division, and signal transduction. Kinases which catalyze the transfer of γ-phosphate groups of nucleotide triphosphates to their substrates are central to the regulation of protein phosphorylation and are therefore important therapeutic targets. Top-down mass spectrometry (MS) presents unique opportunities to study protein kinases owing to its capabilities in comprehensive characterization of proteoforms that arise from alternative splicing, sequence variations, and post-translational modifications. Here, for the first time, we developed a top-down MS method to characterize the catalytic subunit (C-subunit) of an important kinase, cAMP-dependent protein kinase (PKA). The recombinant PKA C-subunit was expressed in Escherichia coli and successfully purified via his-tag affinity purification. By intact mass analysis with high resolution and high accuracy, four different proteoforms of the affinity-purified PKA C-subunit were detected, and the most abundant proteoform was found containing seven phosphorylations with the removal of N-terminal methionine. Subsequently, the seven phosphorylation sites of the most abundant PKA C-subunit proteoform were characterized simultaneously using tandem MS methods. Four sites were unambiguously identified as Ser10, Ser11, Ser18, and Ser30, and the remaining phosphorylation sites were localized to Ser2/Ser3, Ser358/Thr368, and Thr[215-224]Tyr in the PKA C-subunit sequence with a 20mer 6xHis-tag added at the N-terminus. Interestingly, four of these seven phosphorylation sites were located at the 6xHis-tag. Furthermore, we have performed dephosphorylation reaction by Lambda protein phosphatase and showed that all phosphorylations of the recombinant PKA C-subunit phosphoproteoforms were removed by this phosphatase.

Cardiac ischemia-reperfusion injury induces ROS-dependent loss of PKA regulatory subunit RIα.

Type I PKA regulatory α-subunit (RIα; encoded by the Prkar1a gene) serves as the predominant inhibitor protein of the catalytic subunit of cAMP-dependent protein kinase (PKAc). However, recent evidence suggests that PKA signaling can be initiated by cAMP-independent events, especially within the context of cellular oxidative stress such as ischemia-reperfusion (I/R) injury. We determined whether RIα is actively involved in the regulation of PKA activity via reactive oxygen species (ROS)-dependent mechanisms during I/R stress in the heart. Induction of ex vivo global I/R injury in mouse hearts selectively downregulated RIα protein expression, whereas RII subunit expression appears to remain unaltered. Cardiac myocyte cell culture models were used to determine that oxidant stimulus (i.e., H2O2) alone is sufficient to induce RIα protein downregulation. Transient increase of RIα expression (via adenoviral overexpression) negatively affects cell survival and function upon oxidative stress as measured by increased induction of apoptosis and decreased mitochondrial respiration. Furthermore, analysis of mitochondrial subcellular fractions in heart tissue showed that PKA-associated proteins are enriched in subsarcolemmal mitochondria (SSM) fractions and that loss of RIα is most pronounced at SSM upon I/R injury. These data were supported via electron microscopy in A-kinase anchoring protein 1 (AKAP1)-knockout mice, where loss of AKAP1 expression leads to aberrant mitochondrial morphology manifested in SSM but not interfibrillar mitochondria. Thus, we conclude that modification of RIα via ROS-dependent mechanisms induced by I/R injury has the potential to sensitize PKA signaling in the cell without the direct use of the canonical cAMP-dependent activation pathway.NEW & NOTEWORTHY We uncovered a previously undescribed phenomenon involving oxidation-induced activation of PKA signaling in the progression of cardiac ischemia-reperfusion injury. Type I PKA regulatory subunit RIα, but not type II PKA regulatory subunits, is dynamically regulated by oxidative stress to trigger the activation of the catalytic subunit of PKA in cardiac myocytes. This effect may play a critical role in the regulation of subsarcolemmal mitochondria function upon the induction of ischemic injury in the heart.

CoQ10 production in Schizosaccharomyces pombe is increased by reduction of glucose levels or deletion of pka1.

Coenzyme Q (CoQ) is an essential component of the electron transport system that produces ATP in nearly all living cells. CoQ10 is a popular commercial food supplement around the world, and demand for efficient production of this molecule has increased in recent years. In this study, we explored CoQ10 production in the fission yeast Schizosaccharomyces pombe. We found that CoQ10 level was higher in stationary phase than in log phase, and that it increased when the cells were grown in a low concentration of glucose, in maltose, or in glycerol/ethanol medium. Because glucose signaling is mediated by cAMP, we evaluated the involvement of this pathway in CoQ biosynthesis. Loss of Pka1, the catalytic subunit of cAMP-dependent protein kinase, increased production of CoQ10, whereas loss of the regulatory subunit Cgs1 decreased production. Manipulation of other components of the cAMP-signaling pathway affected CoQ10 production in a consistent manner. We also found that glycerol metabolism was controlled by the cAMP/PKA pathway. CoQ10 production by the S. pombe ∆pka1 reached 0.98mg/g dry cell weight in medium containing a non-fermentable carbon source [2% glycerol (w/v) and 1% ethanol (w/v) supplemented with 0.5% casamino acids (w/v)], twofold higher than the production in wild-type cells under normal growth conditions. These findings demonstrate that carbon source, growth phase, and the cAMP-signaling pathway are important factors in CoQ10 production in S. pombe.

Zooming in on protons: Neutron structure of protein kinase A trapped in a product complex.

The question vis-à-vis the chemistry of phosphoryl group transfer catalyzed by protein kinases remains a major challenge. The neutron diffraction structure of the catalytic subunit of cAMP-dependent protein kinase (PKA-C) provides a more complete chemical portrait of key proton interactions at the active site. By using a high-affinity protein kinase substrate (PKS) peptide, we captured the reaction products, dephosphorylated nucleotide [adenosine diphosphate (ADP)] and phosphorylated PKS (pPKS), bound at the active site. In the complex, the phosphoryl group of the peptide is protonated, whereas the carboxyl group of the catalytic Asp166 is not. Our structure, including conserved waters, shows how the peptide links the distal parts of the cleft together, creating a network that engages the entire molecule. By comparing slow-exchanging backbone amides to those determined by the NMR analysis of PKA-C with ADP and inhibitor peptide (PKI), we identified exchangeable amides that likely distinguish catalytic and inhibited states.

Globally correlated conformational entropy underlies positive and negative cooperativity in a kinase\u2019s enzymatic cycle

Enzymes accelerate the rate of chemical transformations by reducing the activation barriers of uncatalyzed reactions. For signaling enzymes, substrate recognition, binding, and product release are often rate-determining steps in which enthalpy-entropy compensation plays a crucial role. While the nature of enthalpic interactions can be inferred from structural data, the molecular origin and role of entropy in enzyme catalysis remains poorly understood. Using thermocalorimetry, NMR, and MD simulations, we studied the conformational landscape of the catalytic subunit of cAMP-dependent protein kinase A, a ubiquitous phosphoryl transferase involved in a myriad of cellular processes. Along the enzymatic cycle, the kinase exhibits positive and negative cooperativity for substrate and nucleotide binding and product release. We found that globally coordinated changes of conformational entropy activated by ligand binding, together with synchronous and asynchronous breathing motions of the enzyme, underlie allosteric cooperativity along the kinase’s cycle.

High immunological response against a Trypanosoma equiperdum protein that exhibits homology with the regulatory subunits of mammalian cAMP-dependent protein kinases

ABSTRACTPreviously, we have identified a protein in Trypanosoma equiperdum that possesses homology with the regulatory (R) subunits of the mammalian cAMP-dependent protein kinase (PKA). The recombinant T. equiperdum PKA R-like protein was expressed in bacteria and purified to homogeneity. Mice polyclonal antibodies were raised against the recombinant R-like protein to serologically evaluate its humoral immune response. High titers of specific sera antibodies were obtained against the parasite R-like protein by indirect enzyme-linked immunosorbent assay (ELISA), and immunoblots revealed that this protein was specifically recognized by the hyperimmune mice sera. Cellular proliferation assays using splenic B cells from the immunized mice showed higher values when the recombinant T. equiperdum R-like protein was employed than when concanavalin A was utilized as an unspecific mitogen. Two healthy horses that were experimentally infected using either T. equiperdum or Trypanosoma evansi showed a curve response characterized by the appearance of anti-T. equiperdum PKA R-like protein antibody production in sera using indirect ELISA. The recombinant parasite PKA R-like protein was also recognized by sera from naturally trypanosome-infected horses using western blotting. These findings demonstrated that the T. equiperdum PKA R-like protein is an antigen that exhibits cross-reaction with T. equiperdum and T. evansi.

Conformation and dynamics of intrinsically disordered microtubule associated protein 2c (MAP2c)

Microtubule associated protein 2c (MAP2c) regulates structure and dynamics (polymerization and degradation) of microtubules in developing neurons and other cells. MAP2c is a 49 kDa intrinsically disordered protein (IDP) consisting of several structural and functional regions. The N-terminal part contains two important regions: An N-terminal region with a high content of negatively charged amino acids and a proline-rich region. The former segment contains a binding site for the regulatory subunit of cAMP-dependent protein kinase (PKA) and proposed binding site for steroids, while the latter one contains several phosphorylation sites. The second important part of MAP2c is a highlyconserved C-terminal domain that binds to microtubules. In order to investigate relation between highly dynamic structural features of MAP2c and its functions, we studied dynamics of MAP2c using nuclear magnetic resonance (NMR) relaxation and performed quantitative conformational analysis of NMR chemical shifts, small angle X-ray scattering, and paramagnetic relaxation enhancement. Pools of possible chain conformations were generated by the program Flexible-Meccano, which builds consecutively a polypeptide chain. The ensemble of structures reproducing the experimental data was selected by the program ASTEROIDS which uses a genetic algorithm. We found out that the least flexible amino acids are involved in transient long-range contacts between the acidic N-terminal domain and the microtubule-binding domain and that more ordered regions correlate with the regions of known or proposed function. Our results thus indicate importance of the N-terminal regions for the specificity of regulatory roles of MAP2c and a close relation between biological functions and conformational behavior of this protein

ProtaTETHER - a method for the incorporation of variable linkers in protein fusions reveals impacts of linker flexibility in a PKAc-GFP fusion protein.

Protein fusions are of fundamental importance in the study of cellular biology and the elucidation of cell signaling pathways, and the importance of linkers for the proper function of protein fusions is well documented in the literature. However, there are few convenient methods available to experimentalists for the systematic implementation of linkers in protein fusions. In this work, we describe a universal approach to the creation and insertion of focused linker libraries into protein fusions. This process, deemed protaTETHER, utilizes reiterative oligomer design, PCR‐mediated linker library generation, and restriction enzyme‐free cloning methods in a straightforward, three‐step cloning process. We utilize a fusion between the catalytic subunit of cAMP‐dependent protein kinase A (PKAc) and green fluorescent protein (GFP) for the development of the protaTETHER method, implementing small linker libraries that vary by length, sequence, and predicted secondary structural elements. We analyze the impact of linker length and sequence on the expression, activity, and subcellular localization of the PKAc‐GFP fusions, and use these results to select a PKAc‐GFP fusion construct with robust expression and enzymatic activity. Based upon the results of both biochemical experiments and molecular modeling, we determine that linker flexibility is more important than linker length for optimal kinase activity and expression.

Gα-cAMP/PKA pathway positively regulates pigmentation, chaetoglobosin A biosynthesis and sexual development in Chaetomium globosum.

Sensing the environmental signals, the canonical Gα-cAMP/PKA pathway modulates mycelial growth and development, and negatively regulates some secondary metabolism in filamentous fungi, e.g. aflatoxin in Aspergillus nidulans. Here we report the characterization of this signaling pathway in Chaetomium globosum, a widely spread fungus known for synthesizing abundant secondary metabolites, e.g. chaetoglobosin A (ChA). RNAi-mediated knockdown of a putative Gα-encoding gene gna-1, led to plural changes in phenotype, e.g. albino mycelium, significant restriction on perithecium development and decreased production of ChA. RNA-seq profiling and qRT-PCR verified significantly fall in expression of corresponding genes, e.g. pks-1 and CgcheA. These defects could be restored by simultaneous knock-down of the pkaR gene encoding a regulatory subunit of cAMP-dependent protein kinase A (PKA), suggesting that pkaR had a negative effect on the above mentioned traits. Confirmatively, the intracellular level of cAMP in wild-type strain was about 3.4-fold to that in gna-1 silenced mutant pG14, and addition of a cAMP analog, 8-Br-cAMP, restored the same defects, e.g., the expression of CgcheA. Furthermore, the intracellular cAMP in gna-1 and pkaR double silenced mutant was approaching the normal level. The following activity inhibition experiment proved that the expression of CgcheA was indeed regulated by PKA. Down-regulation of LaeA/VeA/SptJ expression in gna-1 mutant was also observed, implying that Gα signaling may crosstalk to other regulatory pathways. Taken together, this study proposes that the heterotrimeric Gα protein-cAMP/PKA signaling pathway positively mediates the sexual development, melanin biosynthesis, and secondary metabolism in C. globosum.

ProtaTETHER: A method for the incorporation of variable linker sequences in protein fusions

Protein fusions are of fundamental importance in the study of cellular biology and the elucidation of cell signaling pathways, and the importance of linker design for the proper function of protein fusions is well documented in the literature. However, there are few robust and convenient methods available to experimentalists for the systematic implementation and evaluation of linkers in protein fusions. In this work, we describe a universal approach to the creation and insertion of focused linker libraries into protein fusions, enabling the creation of multiple variants for assessing the impact of linker length and sequence on fusion activity, expression, and localization. This process, deemed protaTETHER, utilizes reiterative oligomer design, PCR-mediated linker library generation, and restriction enzyme-free cloning methods in a straightforward, three-step cloning process. We utilize a fusion between the catalytic subunit of cAMP-dependent protein kinase A (PKAcs) and green fluorescent protein (GFP) for development of the protaTETHER method, implementing small linker libraries that vary by length, sequence, and predicted secondary structural elements. We analyze the impact of linker length and sequence on the expression, activity, and subcellular localization of the PKAcs-GFP construct, and use these results to select a PKAcs-GFP fusion with both robust expression and enzymatic activity. We also discuss additional areas of protein design in which the protaTETHER process may be of use. Support or Funding Information East Carolina University Division of Research, Economic Development, and Engagement The protaTETHER method combines PCR-mediated linker generation with a restriction enzyme-free cloning method to incorporate focused linker libraries into protein fusions. The resulting fusions are then evaluated in parallel for expression and activity. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Competitive ligands facilitate dissociation of the complex of bifunctional inhibitor and protein kinase

Dissociation of the complex of a ligand and a protein usually follows the kinetic profile of the first order process and the rate of dissociation is not affected by the presence of competitive ligands. We discovered that dissociation of the complex between a bifunctional ligand and a protein kinase (the catalytic subunit of cAMP-dependent protein kinase), an enzyme possessing 2 different substrate binding sites, was accelerated (facilitated) over 50-fold in the presence of competitive ligands at higher concentrations. Structurally diverse compounds revealed >10-fold different efficiency for acceleration of dissociation of the complex. These results show that the kinetic behavior of flexible biomolecular complexes possessing two spatially separated contact areas is highly dynamic. This property of biomolecular complexes should be carefully considered for effective application of bifunctional ligands for regulation of activity of target proteins in cells.

Characterization of PKACα enzyme kinetics and inhibition in an HPLC assay with a chromophoric substrate

Here we describe a convenient, inexpensive, and non-hazardous method for the measurement of the kinase activity of the catalytic subunit of cAMP-dependent protein kinase (PKACα). The assay is based on the separation of a substrate peptide labeled with a strong chromophore from the phosphorylated product peptide by high-performance liquid chromatograph (HPLC) and quantification of the product ratiometrically at a wavelength in the visual spectrum (Vis). The utility and reliability of the HPLC-Vis assay were demonstrated by characterizing the kinetic parameters (KM, Vmax) of the new Rh-MAB-Kemptide substrate, a commercially prepared TAMRA-Kemptide substrate, and ATP as well as the potency (IC50, Ki) of the known PKACα inhibitors H89 and PKI(5-24). The advantages of this assay are that it is convenient and inexpensive, uses readily synthesized or commercially available substrates that are shelf-stable, uses a common piece of laboratory equipment, and does not require any hazardous materials such as radioactive γ-32P-ATP. The assay format is also highly flexible and could be adapted for the testing of many different kinases by changing the peptide substrate sequence.

Design, synthesis, and in vitro evaluation of a fluorescently labeled irreversible inhibitor of the catalytic subunit of cAMP-dependent protein kinase (PKACα).

The design and development of irreversible kinase inhibitors is an expanding frontier of kinase drug discovery. The current approach to develop these inhibitors utilizes ATP-competitive inhibitor scaffolds to target non-catalytic cysteines in the kinase ATP-binding site. However, this approach is limited as not all kinases have a cysteine in the ATP-binding site that can be targeted. In this work, we report a complementary approach to developing irreversible kinase inhibitors that utilizes the substrate-binding site. Using the catalytic subunit of cAMP-dependent protein kinase (PKACα) as a model system, we have designed and synthesized an irreversible inhibitor based on the substrate-competitive inhibitor scaffold PKI(14-22) that covalently modifies non-catalytic Cys199 in the PKACα substrate-binding site. The new compound inhibits PKACα (IC50 = 11.8 ± 1.1 nM), is ∼100-fold selective for PKACα in a kinase panel, and covalently labels the kinase as demonstrated by fluorescence, mass spectrometry, and kinetics experiments. This study demonstrates the feasibility of utilizing this new approach to develop irreversible inhibitors for any of the eighty-nine kinases that possess a similar non-catalytic cysteine in their substrate-binding sites.

Celecoxib reduces glucocorticoids in vitro and in a mouse model with adrenocortical hyperplasia.

Primary pigmented nodular adrenocortical disease (PPNAD), whether in the context of Carney complex (CNC) or isolated, leads to ACTH-independent Cushing's syndrome (CS). CNC and PPNAD are caused typically by inactivating mutations of PRKAR1A, a gene coding for the type 1a regulatory subunit (R1α) of cAMP-dependent protein kinase (PKA). Mice lacking Prkar1a, specifically in the adrenal cortex (AdKO) developed CS caused by bilateral adrenal hyperplasia (BAH), which is formed from the abnormal proliferation of fetal-like adrenocortical cells. Celecoxib is a cyclooxygenase 2 (COX2) inhibitor. In bone, Prkar1a inhibition is associated with COX2 activation and prostaglandin E2 (PGE2) production that, in turn, activates proliferation of bone stromal cells. We hypothesized that COX2 inhibition may have an effect in PPNAD. In vitro treatment of human cell lines, including one from a patient with PPNAD, with celecoxib resulted in decreased cell viability. We then treated AdKO and control mice with 1500 mg/kg celecoxib or vehicle. Celecoxib treatment led to decreased PGE2 and corticosterone levels, reduced proliferation and increased apoptosis of adrenocortical cells, and decreased steroidogenic gene expression. We conclude that, in vitro and in vivo, celecoxib led to decreased steroidogenesis. In a mouse model of PPNAD, celecoxib caused histological changes that, at least in part, reversed BAH and this was associated with a reduction of corticosterone levels.

High-resolution crystal structure of cAMP-dependent protein kinase from Cricetulus griseus.

Protein kinases (PKs) are dynamic regulators of numerous cellular processes. Their phosphorylation activity is determined by the conserved kinase core structure, which is maintained by the interaction and dynamics with associated domains or interacting proteins. The prototype enzyme for investigations to understand the activity and regulation of PKs is the catalytic subunit of cAMP-dependent protein kinase (PKAc). Major effects of functional regulation and ligand binding are driven by only minor structural modulations in protein-protein interactions. In order to resolve such minor structural differences, very high resolution structures are required. Here, the high-resolution X-ray structure of PKAc from Cricetulus griseus is reported.

Phosphorylation properties of twitchin from Yesso scallop catch and striated muscles

Molluscan smooth muscle exhibits a unique muscle contraction, called catch, where the tension is maintained for long periods with little energy consumption. Catch contraction is regulated by twitchin, also called mini-titin, a member of the titin/connectin family. Twitchin is also found in molluscan non-catch striated muscle. We isolated twitchins from catch and striated muscles in the Yesso scallop Mizuhopecten yessoensis. Both twitchins are ~500 kDa in size. Western blotting using the anti-twitchin kinase domain antibody revealed that both twitchins have a kinase domain. Both twitchins were phosphorylated by the catalytic subunit of cAMP-dependent protein kinase in vitro. Stoichiometric analysis revealed that 0.6 and 1.7 mol Pi were incorporated into catch and striated muscle twitchins, respectively. Phosphopeptide mapping revealed that catch muscle twitchin has one phosphorylation site, whereas striated muscle twitchin has two. cDNA cloning gave partial sequences of two Yesso scallop twitchin isoforms. One had two putative phosphorylation sites and the other had one.

Selected 4-phenyl hydroxycoumarins: In vitro cytotoxicity, teratogenic effect on zebrafish (Danio rerio) embryos and molecular docking study

A study of structure cytotoxic–activity relationship of three hydroxy 4-phenyl-coumarins and basic coumarin molecule against two human cell lines (MRC5 fibroblasts and A375 melanoma cells) is presented. Of all investigated compounds the highest cytotoxic activity in both cell lines was determined for 7,8-dihydroxy-4-phenyl coumarin. SAR studies revealed the influence of phenyl group and hydroxyl group’s number and position on cytotoxic activity. In addition, to get an insight about their binding preferences at the active site of the receptor (catalytic subunit of cAMP-dependent protein kinase) molecular docking studies were performed. Docking studies suggest that 4-phenyl hydroxycoumarins are potent cAMP-dependent protein kinase inhibitors, better than their analogs without phenyl group. The teratogenic potential was assessed in zebrafish embryo toxicity test and results showed that 4-phenyl dihydroxycoumarins were more while 7-hydroxy-4-phenyl coumarin was less embryo toxic in comparison to coumarin. In order to examine selected 4-phenyl hydroxycoumarins as a new lead compounds the druglikeness of selected 4-phenyl hydroxycoumarins was estimated by using Lipinski’s “rule of five”. All selected 4-phenyl hydroxycoumarins proved to have satisfying pharmacokinetic profile.

Bisubstrate Inhibitor Approach for Targeting Mitotic Kinase Haspin

During the past decade, the basophilic atypical kinase Haspin has emerged as a key player in mitosis responsible for phosphorylation of Thr3 residue of histone H3. Here, we report the construction of conjugates comprising an aromatic fragment targeted to the ATP-site of Haspin and a peptide mimicking the N-terminus of histone H3. The combination of effective solid phase synthesis procedures and a high throughput binding/displacement assay with fluorescence anisotropy readout afforded the development of inhibitors with remarkable subnanomolar affinity toward Haspin. The selectivity profiles of novel conjugates were established by affinity studies with a model basophilic kinase (catalytic subunit of cAMP-dependent protein kinase) and by a commercial 1-point inhibition assay with 43 protein kinases.

A soluble phosphodiesterase in Leishmania donovani negatively regulates cAMP signaling by inhibiting protein kinase A through a two way process involving catalytic as well as non-catalytic sites

Intracellular cAMP level and cAMP mediated responses are elevated when Leishmania are exposed to macrophage phagolysosome conditions (37°C and pH 5.5). Phosphodiesterases play major role in cAMP regulation and in the present study we have cloned and characterized a 2.1kb cytosolic isoform of phosphodiesterase from Leishmania donovani (LdPDED) which plays important role in cAMP homeostasis when the promastigotes are exposed to macrophage phagolysome conditions for converting to axenic amastigotes. Domain characterization suggested the presence of two pseudo-substrate sites similar to the ones present in the regulatory subunit of cAMP-dependent protein kinase A (PKA) and a putative PKA phosphorylation site at T708 of C-terminus of LdPDED. Deletion constructs and site directed mutagenesis revealed the ability of LdPDED to interact with L. donovani PKA catalytic subunits (LdPKAC1 and LdPKAC2) resulting in inhibition of kinase activity in one hand and increase of phosphodiesterase activity through PKA mediated phosphorylation at putative phosphorylation site on the other hand. This study therefore identifies a unique phosphodiesterase in L. donovani which appears to regulate cAMP-dependent PKA signaling through a two way process.