ATP Analog Research Articles

Physiological and pharmacological characterization of the N1303K mutant CFTR

BackgroundN1303K, one of the common, severe disease-causing mutations in the CFTR gene, causes both defective biogenesis and gating abnormalities of the CFTR protein. The goals of the present study are to quantitatively assess the gating defects associated with the N1303K mutation and its pharmacological response to CFTR modulators including potentiators VX-770 and GLPG1837 and correctors VX-809, and VX-661. MethodsGating behavior and pharmacological responses to CFTR potentiators were assessed using patch-clamp technique in the excised, inside-out mode. We also examined the effects of GLPG1837, VX-770, VX-809 and VX-661 on N1303K-CFTR surface expression using Western blot analysis. ResultsLike wild-type (WT) CFTR, N1303K-CFTR channels were activated by protein kinase A-dependent phosphorylation, but the open probability (Po) of phosphorylated N1303K-CFTR was extremely low (~0.03 vs ~0.45 in WT channels). N1303K mutants showed abnormal responses to ATP analogs or mutations that disrupt ATP hydrolysis and/or dimerization of CFTR's two nucleotide-binding domains (NBDs). However, the Po of N1303K-CFTR was dramatically increased by GLPG1837 (~17-fold) and VX-770 (~8-fold). VX-809 or VX-661 enhanced N1303K-CFTR maturation by 2–3 fold, and co-treatment with GLPG1837 or VX-770 did not show any negative drug-drug interaction. ConclusionN1303K has a severe gating defect, reduced ATP-dependence and aberrant response to ATP analogs. These results suggest a defective function of the NBDs in N1303K-CFTR. An improvement of channel function by GLPG1837 or VX-770 and an increase of Band C protein by VX-809 or VX-661 support a therapeutic strategy of combining CFTR potentiator and corrector for patients carrying the N1303K mutation.

Insulin regulates astrocyte gliotransmission and modulates behavior.

Complications of diabetes affect tissues throughout the body, including the central nervous system. Epidemiological studies show that diabetic patients have an increased risk of depression, anxiety, age-related cognitive decline, and Alzheimer's disease. Mice lacking insulin receptor (IR) in the brain or on hypothalamic neurons display an array of metabolic abnormalities; however, the role of insulin action on astrocytes and neurobehaviors remains less well studied. Here, we demonstrate that astrocytes are a direct insulin target in the brain and that knockout of IR on astrocytes causes increased anxiety- and depressive-like behaviors in mice. This can be reproduced in part by deletion of IR on astrocytes in the nucleus accumbens. At a molecular level, loss of insulin signaling in astrocytes impaired tyrosine phosphorylation of Munc18c. This led to decreased exocytosis of ATP from astrocytes, resulting in decreased purinergic signaling on dopaminergic neurons. These reductions contributed to decreased dopamine release from brain slices. Central administration of ATP analogs could reverse depressive-like behaviors in mice with astrocyte IR knockout. Thus, astrocytic insulin signaling plays an important role in dopaminergic signaling, providing a potential mechanism by which astrocytic insulin action may contribute to increased rates of depression in people with diabetes, obesity, and other insulin-resistant states.

Bisphosphonate-Generated ATP-Analogs Inhibit Cell Signaling Pathways.

Bisphosphonates are a major class of drugs used to treat osteoporosis, Paget's disease, and cancer. They have been proposed to act by inhibiting one or more targets including protein prenylation, the epidermal growth factor receptor, or the adenine nucleotide translocase. Inhibition of the latter is due to formation in cells of analogs of ATP: the isopentenyl ester of ATP (ApppI) or an AppXp-type analog of ATP, such as AMP-clodronate (AppCCl2p). We screened both ApppI as well as AppCCl2p against a panel of 369 kinases finding potent inhibition of some tyrosine kinases by AppCCl2p, attributable to formation of a strong hydrogen bond between tyrosine and the terminal phosphonate. We then synthesized bisphosphonate preprodrugs that are converted in cells to other ATP-analogs, finding low nM kinase inhibitors that inhibited cell signaling pathways. These results help clarify our understanding of the mechanisms of action of bisphosphonates, potentially opening up new routes to the development of bone resorption, anticancer, and anti-inflammatory drug leads.

The role of ATP and P2X purinoreceptor 7 in the pathogenesis of cerebral tau

The tauopathies are a group of neurodegenerative diseases characterized by abnormal deposition of hyperphosphorylated-tau. The pathogenesis of these changes remains uncertain. In chronic traumatic encephalopathy, tauopathy is hypothesized to occur after repeated mild traumatic brain injury (TBI). Post-traumatic extracellular ATP release and signalling via the P2X purinoceptor 7 (P2RX7) has been shown to be important in mediating pathological changes in TBI. We hypothesized that ATP-P2RX7 is involved in the development of tauopathy.We injected ATP analogue bzATP or vehicle intraventricularly into C57BL/6 mice, pre-treated with either intraperitoneal P2RX7 antagonist Brilliant Blue G (BBG) or vehicle. At 2 weeks and 3 months, behavioural change was assessed with the tail suspension test, accelerating rotatrod, and fear conditioning; mice were then sacrificed for immunohistochemistry and western blot.We observed increased immobile time in the tail suspension test for mice treated with bzATP at 3 months. Similarly, for rotarod, mice treated with bzATP showed poorer performance at 3 months. These effects were diminished by BBG pre-treatment. Fear conditioning, however, did not demonstrate a significant difference between groups. Immunohistochemical staining for GFAP showed increased intensity at both 2 weeks and 3 months for bzATP-treated mice compared to those pre-treated with BBG. Levels of phosphorylated tau (AT8) were increased in bzATP-treated mice compared to controls.In summary, ATP-P2RX7-mediated mechanisms may play a role in the development of behavioural deficits and tauopathy.

Dynamics-based community analysis and perturbation response scanning of allosteric interaction networks in the TRAP1 chaperone structures dissect molecular linkage between conformational asymmetry and sequential ATP hydrolysis

Allosteric interactions of the Hsp90 chaperones with cochaperones and diverse protein clients can often exhibit distinct asymmetric features that determine regulatory mechanisms and cellular functions in many signaling networks. The recent crystal structures of the mitochondrial Hsp90 isoform TRAP1 in complexes with ATP analogs have provided first evidence of significant asymmetry in the closed dimerized state that triggers independent activity of the chaperone protomers, whereby preferential hydrolysis of the buckled protomer is followed by conformational flipping between protomers and hydrolysis of the second protomer. Despite significant insights in structural characterizations of the TRAP1 chaperone, the atomistic details and mechanics of allosteric interactions that couple sequential ATP hydrolysis with asymmetric conformational switching in the TRAP1 protomers remain largely unknown. In this work, we explored atomistic and coarse-grained simulations of the TRAP1 dimer structures in combination with the ensemble-based network modeling and perturbation response scanning of residue interaction networks to probe salient features underlying allosteric signaling mechanism. This study has revealed that key effector sites that orchestrate allosteric interactions occupy the ATP binding region and N-terminal interface of the buckled protomer, whereas the main sensors of allosteric signals that drive functional conformational changes during ATPase cycle are consolidated near the client binding region of the straight protomer, channeling the energy of ATP hydrolysis for client remodeling. The community decomposition analysis of the interaction networks and reconstruction of allosteric communication pathways in the TRAP1 structures have quantified mechanism of allosteric regulation, revealing control points and interactions that coordinate asymmetric switching during ATP hydrolysis.

Mechanistic Studies of Drug‐Like Inhibitors of P‐glycoprotein using ATPase Assays, Electron Spin Resonance Spectroscopy and Cancer Cell Models

Multidrug resistance (MDR) in cancer and other diseases is frequently associated with transmembrane efflux proteins, one of which is P‐glycoprotein (P‐gp). Over‐expression of P‐gp in cancer cells increases the efflux of therapeutic drugs rendering them ineffective. In order to re‐sensitize multidrug resistant cancers to chemotherapy, we have found inhibitors of P‐gp by in silico screening methods (Brewer et al., Molecular pharmacology 86, 716–726, 2014), and several of these inhibitors were shown to successfully overcome MDR in the drug resistant DU145TXR prostate cancer cell line (Follit et al., Pharmacol. Res. Perspect. 3, e00170, 2015). In this study, we expanded our cell culture screening to evaluate 25 new compounds identified by our in silico screening method and report that over 30% of these compounds re‐sensitized DU145TXR cancer cells to chemotherapy, while not exhibiting significant toxicity to the non‐cancerous human lung fibroblast (HFL‐1) cell line. The best of the identified hit compounds were further investigated with regard to the mechanism of inhibition using ATPase activity assays and electron spin resonance spectroscopy (ESR). Several of the best compounds were found to inhibit ATPase activity. Using a spin‐labeled ATP analog and ESR spectroscopy, we assessed the effects of the identified inhibitors on ATP binding to P‐gp. Variants of one of the original hit compounds, SMU 29, that were computationally predicted to interact more strongly with P‐gp have been synthesized and were analyzed here for their effects on P‐gp ATPase activity and ATP binding characteristics.Support or Funding InformationThis work is supported by NIH NIGMS [R15GM094771‐02] to John G. Wise, SMU University Research Council, the SMU Center for Drug Discovery, Design and Delivery, the Communities Foundation of Texas, and a private gift from Ms. Suzy Ruff of Dallas, Texas, as well as the Hamilton Undergraduate Research Scholars Program and the SMU Summer Research Assistantship and Undergraduate Research Assistantship Programs.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

“Thermodynamic Analysis of ATP Dissociation in a DEAD‐Box Protein”

RNA plays an essential role in many cellular functions. Similar to proteins, RNA function is strictly determined by the overall structure and dynamics of the RNA macromolecule. Thus, many cellular proteins or accessory factors are associated with RNA folding. One example of these RNA binding proteins are DEAD‐Box proteins. DEAD‐Box proteins utilize ATP hydrolysis to unwind and reanneal RNA duplexes to promote correct folding during RNA processing. DEAD‐Box proteins possess two conserved RecA‐like domains that bind ATP and RNA. In addition, these proteins also contain N‐ and/or C‐ terminal domains (NTD and CTD, respectively). Peripheral domains in DEAD‐Box proteins are proposed to regulate ATP hydrolysis as well as confer RNA specificity. Thus, the NTD and/or CTD can alter the ATP binding pocket and subsequently alter ATP association and/or dissociation. For example, Rok1p, a yeast DEAD‐Box protein, contains both a NTD and a CTD. The NTD in Rok1p is suggested to affect the structure and stability of the protein. Therefore, the dissociation rate of a fluorescence ATP analog was determined through transient kinetics and stopped‐flow spectroscopy under various thermal conditions. Resulting trends conform to double exponential fits suggesting a two‐step mechanism. The observed slow rate was consistent with a conformation change in the protein that allows rapid dissociation. The rate in which the conformation change occurs was observed to be temperature dependent. The current hypothesis centers on the ability, of the Rok1p peripheral domains, to affect the slow structural change needed for ATP dissociation.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A chemical genetic approach to engineer phototropin kinases for substrate labeling

Protein kinases (PKs) control many aspects of plant physiology by regulating signaling networks through protein phosphorylation. Phototropins (phots) are plasma membrane-associated serine/threonine PKs that control a range of physiological processes that collectively serve to optimize photosynthetic efficiency in plants. These include phototropism, leaf positioning and flattening, chloroplast movement, and stomatal opening. Despite their identification over two decades ago, only a handful of substrates have been identified for these PKs. Progress in this area has been hampered by the lack of a convenient means to confirm the identity of potential substrate candidates. Here we demonstrate that the kinase domain of Arabidopsis phot1 and phot2 can be successfully engineered to accommodate non-natural ATP analogues by substituting the bulky gatekeeper residue threonine for glycine. This approach circumvents the need for radioactivity to track phot kinase activity and follow light-induced receptor autophosphorylation in vitro by incorporating thiophosphate from N6-benzyl-ATPγS. Consequently, thiophosphorylation of phot substrate candidates can be readily monitored when added or co-expressed with phots in vitro Furthermore, gatekeeper-modified phot1 retained its functionality and its ability to accommodate N6-benzyl-ATPγS as a phosphodonor when expressed in Arabidopsis We therefore anticipate that this chemical genetic approach will provide new opportunities for labeling and identifying substrates for phots and other related AGC kinases under in vitro and near-native in vivo conditions.

Engineering a Dual Small Molecule Gated ZAP70 Switch in T Cells.

T cells expressing tumor-specific T cell receptors are promising cancer therapeutic agents, but safety control switches are needed to manage potential side effects arising from overactivity. Here, we present the first dual small molecule-gated ZAP70 signaling switch for the regulation of T cell activity. We show that when an analogue-sensitive ZAP70 allele is fused to the engineered ligand binding domain of the estrogen receptor, ERT2, its activity can be upregulated to an extent by a metabolite of an FDA-approved tamoxifen, 4-hydroxy-tamoxifen, and downregulated by an ATP analogue, 3-MB-PP1. The strength of early T cell signaling can also be modulated by varying the concentrations of activator and inhibitor, and the switch exhibits temporal control on the time scale of minutes. Interestingly, the switch has the ability to control CD69 and calcium levels in T cells but has limited capabilities in the regulation of downstream cytokine release, suggesting further investigation is needed before it can be implemented in adoptive T cell therapy.

Kinase-catalyzed biotinylation of DNA

Prior work documented use of γ-phosphate modified ATP analogs to label DNA using T4 polynucleotide kinases (T4PNK), although applications have been limited. To fully characterize kinase-catalyzed labeling of nucleic acids, we explored use of ATP-biotin as a cosubstrate with T4PNK. T4PNK accepted ATP-biotin to 5′-label single stranded DNA. However, T4PNK-mediated labeling of double stranded substrates was low yielding. In addition, the phosphoramidate bond connecting the biotin group to the DNA was unstable. These results suggest that kinase-catalyzed biotinylation will be useful with single stranded DNA substrates and mild reaction conditions. By revealing the scope and limitations of kinase-catalyzed biotinylation, these studies provide a foundation for future development and application of kinase-catalyzed labeling to DNA-based biological studies.

Molecular mechanism of ATP versus GTP selectivity of adenylate kinase

Enzymatic substrate selectivity is critical for the precise control of metabolic pathways. In cases where chemically related substrates are present inside cells, robust mechanisms of substrate selectivity are required. Here, we report the mechanism utilized for catalytic ATP versus GTP selectivity during adenylate kinase (Adk) -mediated phosphorylation of AMP. Using NMR spectroscopy we found that while Adk adopts a catalytically competent and closed structural state in complex with ATP, the enzyme is arrested in a catalytically inhibited and open state in complex with GTP. X-ray crystallography experiments revealed that the interaction interfaces supporting ATP and GTP recognition, in part, are mediated by coinciding residues. The mechanism provides an atomic view on how the cellular GTP pool is protected from Adk turnover, which is important because GTP has many specialized cellular functions. In further support of this mechanism, a structure-function analysis enabled by synthesis of ATP analogs suggests that a hydrogen bond between the adenine moiety and the backbone of the enzyme is vital for ATP selectivity. The importance of the hydrogen bond for substrate selectivity is likely general given the conservation of its location and orientation across the family of eukaryotic protein kinases.

Structural basis for (p)ppGpp synthesis by the Staphylococcus aureus small alarmone synthetase RelP

The stringent response is a global reprogramming of bacterial physiology that renders cells more tolerant to antibiotics and induces virulence gene expression in pathogens in response to stress. This process is driven by accumulation of the intracellular alarmone guanosine-5'-di(tri)phosphate-3'-diphosphate ((p)ppGpp), which is produced by enzymes of the RelA SpoT homologue (RSH) family. The Gram-positive Firmicute pathogen, Staphylococcus aureus, encodes three RSH enzymes: a multidomain RSH (Rel) that senses amino acid starvation on the ribosome and two small alarmone synthetase (SAS) enzymes, RelQ (SAS1) and RelP (SAS2). In Bacillus subtilis, RelQ (SAS1) was shown to form a tetramer that is activated by pppGpp and inhibited by single-stranded RNA, but the structural and functional regulation of RelP (SAS2) is unexplored. Here, we present crystal structures of S. aureus RelP in two major functional states, pre-catalytic (bound to GTP and the non-hydrolyzable ATP analogue, adenosine 5'-(α,β-methylene)triphosphate (AMP-CPP)), and post-catalytic (bound to pppGpp). We observed that RelP also forms a tetramer, but unlike RelQ (SAS1), it is strongly inhibited by both pppGpp and ppGpp and is insensitive to inhibition by RNA. We also identified putative metal ion-binding sites at the subunit interfaces that were consistent with the observed activation of the enzyme by Zn2+ ions. The structures reported here reveal the details of the catalytic mechanism of SAS enzymes and provide a molecular basis for understanding differential regulation of SAS enzymes in Firmicute bacteria.

QM/MM Study of the Dephosphorylation Mechanism of Adenosine 5′‐(β,γ‐Imido)triphosphate Catalyzed by Sulfolobus Tokodaii Hexokinase

AbstractAdenosine triphosphate (ATP) bound hexokinase crystal structure is important for understanding the functions of hexokinase at the atomic level, but it is hard to obtain such complex because of the easy hydrolysis of ATP. Adenosine 5′‐(β,γ‐imido)triphosphate (AMP‐PNP) is a commonly used non‐hydrolysable ATP analogue for co‐crystallization with many proteins, but the AMP‐PNP function towards hexokinase is still unknown in the literature. In the present paper, we would like to report the dephosphorylation mechanisms of AMP‐PNP catalyzed by the wild‐type Sulfolobus tokodaii hexokinase (StHK) and T116A mutant using quantum mechanical/molecular mechanical (QM/MM) method. The catalytic reactions proceed via a phosphate transfer, followed by a proton transfer in these models. Both StHK and T116A mutant catalyzed reactions are endothermic. The phosphate transfer reaction is the rate‐determining step, and their energy barriers are 15.95 and 22.71 kcal⋅mol−1 for StHK and T116A mutant, respectively. Comparison of the ATP dephosphorylation shows that the catalytic processes by the wild‐type and T116A mutated StHK are passivated. The passivation has been attributed to the linking –NH group of AMP‐PNP. The results are meaningful to a better understand of hexokinase and the functions of AMP‐PNP in cocrystallization.

ATP-Dependent Topology Discrimination by Type IIA Topoisomerases: Implications for below Equilibrium Topology Simplification

Type IIA topoisomerases (Topo IIA) are ubiquitous enzymes that play essential roles in maintaining topological homeostasis and in unlinking chromosomes prior to cell division. Topo IIA enzymes, with the exception of DNA gyrase, regulate DNA topology by removing excess DNA supercoils, and inter- and intra-molecular links, corresponding to catenanes and knots respectively. All Topo IIA utilize ATP for their shared catalytic activity in which the enzyme introduces a transient double-strand break in one segment of DNA and transfers a second segment of DNA through this break. The strand passage reaction is coordinated, and made irreversible, through the hydrolysis of ATP. The hydrolysis energy is also coupled to below equilibrium topology simplification activity of Topo IIA that results in the reduction of supercoiling, linking, and knotting to below equilibrium levels. The mechanism of this below equilibrium relaxation remains speculative. In this study, we investigated the correlation between topology-dependent DNA binding and the level of DNA supercoil reduction for two Topo IIA enzymes that exhibit different levels of below equilibrium relaxation: E. coli Topo IV and yeast Topo II. To determine the effect of ATP on the selection of DNA topology, we measured the topology-dependent binding in the presence of two non-hydrolysable ATP analogues: ATPγS and AMPPNP. Topo IV, but not yeast topo II, shows a weak topology-dependent binding in the absence of ATP analogs. Both enzymes exhibit significantly enhanced DNA topology-dependent binding in the presence of ATPγS and AMPPNP. Simulations of Topo IIA activity that incorporate the measured DNA topology dependent binding affinities indicate that DNA topology dependent binding may be a contributing factor explaining non-equilibrium simplification by type IIA topoisomerases.

RNA Granules: Liquids or Active Condensates?

P granules, RNA/protein assemblies in C. elegans embryos, have been proposed to form by liquid-liquid phase separation (LLPS). LLPS is a spontaneous process that allows molecules to exchange passively between a high-concentration phase (in the granule) and a low-concentration phase (in the cytoplasm). To test this hypothesis, we developed methods to observe P granules ex vivo. Surprisingly, we found that P granules do not behave as simple liquids. Core components of P granules are resistant to dilution, high salt and EDTA, but dissolves in 1,6 hexanediol and SDS, consistent with a gel-like phase held by hydrophobic interactions. Remarkably, addition of ATP leads to very rapid P granule dissolution. In contrast, GTP and non-hydrolyzable ATP analogs have little effect. Manipulations that decrease ATP production in vivo also reduce P granule dynamics in embryos. These observations suggest that P granules are gel-like condensates that are kept dynamic in cells by ATP-consuming reactions. Consistent with this view, the intrinsically-disordered proteins that scaffold P granules form gel-like condensates in vitro. Formation of gel-like phases in RNA granules has been described as non-physiological and implicated in a number of neurodegenerative diseases, including ALS and Huntington's disease. Our findings suggest that gel phases are natural components of RNA granules that are kept liquid-like by ATP-dependent enzymes.

Dynamics of Eukaryotic Histone Exchange with Single Molecule Resolution

Remodelling chromatin structure is important for regulating gene expression, DNA replication and repair and other fundamental nuclear processes. The basic chromatin unit is the nucleosome. SWR1 is a multi-subunit complex, whose chromatin remodelling activity is associated with regulation of gene expression in heterochromatin regions of chromosomes in plants and mammals, and with the cellular response to DNA damage. In yeast, the simplest eukaryotic organism, the SWR1 complex is responsible for the ATP-dependent nucleosome remodelling by exchanging its canonical H2A histone with Htz1 variant (also known as H2A.Z in mammalian cells). In spite of a large number of genetic, biochemical and structural studies on SWR1, its detailed histone exchange mechanism remains largely unknown. To investigate the mechanism of histone exchange by SWR1, we have developed a single-molecule FRET assay, which monitors the interaction between individual nucleosomes and yeast SWR1 complexes in real time. The data show distinct dynamic behaviours in the presence or absence of ATP, or in the presence of non-hydrolysable ATP analogue. We hypothesize that the observed dynamics are important for the removal of canonical H2A histones or deposition of the histone variant Htz1. We anticipate that our data will help elucidate the molecular mechanism of histone exchange by SWR1.

Detection of Novel GyrB Mutations Associated with <i>Escherichia coli </i>Clinical Isolates

The following study is investigating the different GyrB mutations associated with Escherichia coli clinical isolates. The study interrogates part of the ATPase binding site (a.a 132-199) as it covers most of the naturally occurring mutations in GyrB. The following results were obtained: for Arg-136 two isolates had mutations, the first is isolate-1 (Ala-136), and the second is isolate-5 (Cys-136). Gly-164 had no changes for all tested isolates. For Thr-165 only isolate-3 had a change to Ser-165. Accuracy of sequence translation was checked by sequencing both CFT073 and MG1655. The current study presents novel mutations in the GyrB24 subdomain of the gyrase enzyme. These new mutations showed normal enzyme activity (no reduction in ATPase functions) indicating that they might be a result of GyrB interaction with ATP analog molecules rather than antibacterial agents such as coumarins. Furthermore, our findings are supporting the idea that mutations in the GyrB24 would require synchronization with the efflux pumps to maintain antibiotic resistance against coumarins.

Combined roles of ATP and small hairpin RNA in the activation of RIG-I revealed by solution-based analysis.

RIG-I (retinoic acid inducible gene-I) is a cytosolic innate immune protein that senses viral dsRNA with a 5′-triphosphate overhang. Upon interaction with dsRNA a de-repression of the RIG-I CARD domains takes place that ultimately leads to the production of type I interferons and pro-inflammatory cytokines. Here we investigate the RIG-I conformational rearrangement upon interaction with an activating 5′-triphosphate-10-base pair dsRNA hairpin loop (10bp) compared with a less active 5′-triphosphate-8-base pair dsRNA hairpin loop (8bp). We use size-exclusion chromatography–coupled small-angle X-ray scattering (SAXS) and limited tryptic digest experiments to show that that upon binding to 10 bp, but not 8 bp, RIG-I becomes extended and shows greater flexibility, reflecting the release of its CARDs. We also examined the effect of different ATP analogues on the conformational changes of RIG-I/dsRNA complexes. Of the analogues tested, the addition of ATP transition state analogue ADP-AlFx further assisted in the complete activation of RIG-I in complex with 10bp and also to some extent RIG-I bound to 8bp. Together these data provide solution-based evidence for the molecular mechanism of innate immune signaling by RIG-I as stimulated by short hairpin RNA and ATP.

Emissive Synthetic Cofactors: Enzymatic Interconversions of tz A Analogues of ATP, NAD+ , NADH, NADP+ , and NADPH.

A series of enzymatic transformations, which generate visibly emissive isofunctional cofactors based on an isothiazolo[4,3-d]pyrimidine analogue of adenosine (tz A), was developed. Nicotinamide adenylyl transferase condenses nicotinamide mononucleotide and tz ATP to yield Ntz AD+ , which can be enzymatically phosphorylated by NAD+ kinase and ATP or tz ATP to the corresponding Ntz ADP+ . The latter can be engaged in NADP-specific coupled enzymatic transformations involving conversion to Ntz ADPH by glucose-6-phosphate dehydrogenase and reoxidation to Ntz ADP+ by glutathione reductase. The Ntz ADP+ /Ntz ADPH cycle can be monitored in real time by fluorescence spectroscopy.

Rational modification of semaxanib and sunitinib for developing a tumor growth inhibitor targeting ATP binding site of tyrosine kinase

Analysis of the crystal structure of tyrosine kinase in complexation with an ATP analogue, supplemented with the molecular docking studies of semaxanib and sunitinib in the ATP binding site of the enzyme enabled us to make design of a series of tyrosine kinase inhibitors. The combination of pyrrole and indolinone in one molecule and placement of appropriate substituent thereof made the molecule compatible for the hydrophobic sub-pocket of the enzyme. Screening of the compounds over 60 cell line panel of human tumor cell lines identified compound 3a that exhibited GI50 35 nM and 63 nM against MCF7 and MDA-MB-468 cell lines of breast cancer.