RESUMO
HIF-1α is a master regulator of oxygen homeostasis involved in different stages of cancer development. Thus, HIF-1α inhibition represents an interesting target for anti-cancer therapy. It was recently shown that the HIF-1α interaction with NQO1 inhibits proteasomal degradation of the former, thus suggesting that targeting the stability and/or function of NQO1 could lead to the destabilization of HIF-1α as a therapeutic approach. Since the molecular interactions of NQO1 with HIF-1α are beginning to be unraveled, in this review we discuss: (1) Structure-function relationships of HIF-1α; (2) our current knowledge on the intracellular functions and stability of NQO1; (3) the pharmacological modulation of NQO1 by small ligands regarding function and stability; (4) the potential effects of genetic variability of NQO1 in HIF-1α levels and function; (5) the molecular determinants of NQO1 as a chaperone of many different proteins including cancer-associated factors such as HIF-1α, p53 and p73α. This knowledge is then further discussed in the context of potentially targeting the intracellular stability of HIF-1α by acting on its chaperone, NQO1. This could result in novel anti-cancer therapies, always considering that the substantial genetic variability in NQO1 would likely result in different phenotypic responses among individuals.
RESUMO
Human NQO1 [NAD(H):quinone oxidoreductase 1] is a multi-functional and stress-inducible dimeric protein involved in the antioxidant defense, the activation of cancer prodrugs and the stabilization of oncosuppressors. Despite its roles in human diseases, such as cancer and neurological disorders, a detailed characterization of its enzymatic cycle is still lacking. In this work, we provide a comprehensive analysis of the NQO1 catalytic cycle using rapid mixing techniques, including multiwavelength and spectral deconvolution studies, kinetic modeling and temperature-dependent kinetic isotope effects (KIEs). Our results systematically support the existence of two pathways for hydride transfer throughout the NQO1 catalytic cycle, likely reflecting that the two active sites in the dimer catalyze two-electron reduction with different rates, consistent with the cooperative binding of inhibitors such as dicoumarol. This negative cooperativity in NQO1 redox activity represents a sort of half-of-sites activity. Analysis of KIEs and their temperature dependence also show significantly different contributions from quantum tunneling, structural dynamics and reorganizations to catalysis at the two active sites. Our work will improve our understanding of the effects of cancer-associated single amino acid variants and post-translational modifications in this protein of high relevance in cancer progression and treatment.
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Praziquantel is a remarkably effective drug for the treatment of schistosomiasis. It has few side effects, some of which have been attributed to its inactive enantiomer. Few, if any, verified cases of drug resistance have been reported in a clinical setting. The preponderance of scientific evidence suggests that the drug works by dysregulating calcium homeostasis in the worm. Voltage-gated calcium channels have been proposed as the main pharmacological target of praziquantel, although no direct evidence of interaction with this protein is available. Here, the biochemical pharmacology of praziquantel is briefly reviewed and a hypothesis for its mechanism proposed. This hypothesis suggests that the drug works, in part, by disrupting an interaction between a voltage-gated calcium channel (SmCav1B) and an accessory protein, SmTAL1.
Assuntos
Praziquantel/farmacologia , Animais , Humanos , Modelos Biológicos , Praziquantel/química , Praziquantel/uso terapêutico , Esquistossomose/tratamento farmacológicoRESUMO
SmTAL1 is a calcium binding protein from the parasitic worm, Schistosoma mansoni. Structurally it is comprised of two domains - an N-terminal EF-hand domain and a C-terminal dynein light chain (DLC)-like domain. The protein has previously been shown to interact with the anti-schistosomal drug, praziquantel (PZQ). Here, we demonstrated that both EF-hands in the N-terminal domain are functional calcium ion binding sites. The second EF-hand appears to be more important in dictating affinity and mediating the conformational changes which occur on calcium ion binding. There is positive cooperativity between the four calcium ion binding sites in the dimeric form of SmTAL1. Both the EF-hand domain and the DLC-domain dimerise independently suggesting that both play a role in forming the SmTAL1 dimer. SmTAL1 binds non-cooperatively to PZQ and cooperatively to an IQ-motif from SmCav1B, a voltage-gated calcium channel. PZQ tends to strengthen this interaction, although the relationship is complex. These data suggest the hypothesis that SmTAL1 regulates at least one voltage-gated calcium channel and PZQ interferes with this process. This may be important in the molecular mechanism of this drug. It also suggests that compounds which bind SmTAL1, such as six from the Medicines for Malaria Box identified in this work, may represent possible leads for the discovery of novel antagonists.
Assuntos
Alérgenos/metabolismo , Canais Iônicos/química , Praziquantel/farmacologia , Proteínas de Protozoários/metabolismo , Schistosoma mansoni/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Cálcio/metabolismo , Calmodulina/antagonistas & inibidores , Calmodulina/metabolismo , Motivos EF Hand , Canais Iônicos/metabolismo , Íons , Peptídeos/química , Ligação Proteica/efeitos dos fármacos , Domínios Proteicos , Multimerização Proteica/efeitos dos fármacos , Proteólise/efeitos dos fármacos , Proteínas de Protozoários/químicaRESUMO
Praziquantel (PZQ) is the drug of choice for treating infection with worms from the genus Schistosoma. The drug is effective, cheap and has few side effects. However, despite its use in millions of patients for over 40 years its molecular mechanism of action remains elusive. Early studies demonstrated that PZQ disrupts calcium ion homeostasis in the worm and the current consensus is that it antagonises voltage-gated calcium channels. It is hypothesised that disruption of these channels results in uncontrolled calcium ion influx leading to uncontrolled muscle contraction and paralysis. However, other experimental studies have suggested a role for myosin regulatory light chains and adenosine uptake in the drug's mechanism of action. Assuming voltage-gated calcium channels do represent the main molecular target of PZQ, the precise binding site for the drug remains to be identified. Unlike other commonly used anti-parasitic drugs, there are few definitive reports of resistance to PZQ in the literature. The lack of knowledge about PZQ's molecular mechanism(s) undermines our ability to predict how resistance might arise and also hinder our attempts to develop alternative antischistosomal drugs which exploit the same target(s). Some PZQ derivatives have been identified which also kill or paralyse schistosomes in culture. However, none of these are in widespread clinical use. There is a pressing need for fundamental research into the molecular mechanism( s) of action of PZQ. Such research would enable new avenues for antischsistosomal drug discovery.
Assuntos
Praziquantel/uso terapêutico , Animais , Anti-Helmínticos , Transporte Biológico , Canais de Cálcio , Humanos , Schistosoma , EsquistossomicidasRESUMO
Human NAD(P)H:quinone oxidoreductase 1 (NQO1) is a multi-functional protein whose alteration is associated with cancer, Parkinson's and Alzheimer´s diseases. NQO1 displays a remarkable functional chemistry, capable of binding different functional ligands that modulate its activity, stability and interaction with proteins and nucleic acids. Our understanding of this functional chemistry is limited by the difficulty of obtaining structural and dynamic information on many of these states. Herein, we have used hydrogen/deuterium exchange monitored by mass spectrometry (HDXMS) to investigate the structural dynamics of NQO1 in three ligation states: without ligands (NQO1apo), with FAD (NQO1holo) and with FAD and the inhibitor dicoumarol (NQO1dic). We show that NQO1apo has a minimally stable folded core holding the protein dimer, with FAD and dicoumarol binding sites populating binding non-competent conformations. Binding of FAD significantly decreases protein dynamics and stabilizes the FAD and dicoumarol binding sites as well as the monomer:monomer interface. Dicoumarol binding further stabilizes all three functional sites, a result not previously anticipated by available crystallographic models. Our work provides an experimental perspective into the communication of stability effects through the NQO1 dimer, which is valuable for understanding at the molecular level the effects of disease-associated variants, post-translational modifications and ligand binding cooperativity in NQO1.
Assuntos
NAD(P)H Desidrogenase (Quinona)/química , NAD(P)H Desidrogenase (Quinona)/genética , Conformação Proteica , Multimerização Proteica/genética , Doença de Alzheimer/enzimologia , Sítios de Ligação , Estabilidade Enzimática/genética , Humanos , Espectrometria de Massas , NAD(P)H Desidrogenase (Quinona)/ultraestrutura , Neoplasias/enzimologia , Doença de Parkinson/enzimologia , Ligação Proteica/genéticaRESUMO
Chaotropes are compounds which cause the disordering, unfolding and denaturation of biological macromolecules. It is the chaotropicity of fermentation products that often acts as the primary limiting factor in ethanol and butanol fermentations. Since ethanol is mildly chaotropic at low concentrations, it prevents the growth of the producing microbes via its impacts on a variety of macromolecular systems and their functions. Kosmotropes have the opposite effect to chaotropes and we hypothesised that it might be possible to use these to mitigate chaotrope-induced inhibition of Saccharomyces cerevisiae growth. We also postulated that kosmotrope-mediated mitigation of chaotropicity is not quantitatively predictable. The chaotropes ethanol and urea, and compatible solutes glycerol and betaine (kosmotrope), and the highly kosmotropic salt ammonium sulphate all inhibited the growth rate of Saccharomyces cerevisiae in the concentration range 5-15%. They resulted in increased lag times, decreased maximum specific growth rates, and decreased final optical densities. Surprisingly, neither the stress protectants nor ammonium sulphate reduced the inhibition of growth caused by ethanol. Whereas, in some cases, compatible solutes and kosmotropes mitigated against the inhibitory effects of urea. However, this effect was not mathematically additive from the quantification of chao-/kosmotropicity of each individual compound. The potential effects of glycerol, betaine and/or ammonium sulphate may have been reduced or masked by the metabolic production of compatible solutes. It may nevertheless be that the addition of kosmotropes to fermentations which produce chaotropic products can enhance metabolic activity, growth rate, and/or product formation.
Assuntos
Biocombustíveis/microbiologia , Modelos Biológicos , Saccharomyces cerevisiae , Sulfato de Amônio/farmacologia , Betaína/metabolismo , Meios de Cultura/química , Meios de Cultura/farmacologia , Entropia , Etanol/metabolismo , Etanol/farmacologia , Fermentação , Glicerol/metabolismo , Saccharomyces cerevisiae/efeitos dos fármacos , Saccharomyces cerevisiae/crescimento & desenvolvimento , Saccharomyces cerevisiae/metabolismo , Ureia/farmacologiaRESUMO
Human NAD(P)H quinone oxidoreductase (DT-diaphorase, NQO1) exhibits negative cooperativity towards its potent inhibitor, dicoumarol. Here, we addressed the hypothesis that the effects of the two cancer-associated polymorphisms (p.R139W and p.P187S) may be partly mediated by their effects on inhibitor binding and negative cooperativity. Dicoumarol stabilized both variants and bound with much higher affinity for p.R139W than p.P187S. Both variants exhibited negative cooperativity towards dicoumarol; in both cases, the Hill coefficient (h) was approximately 0.5 and similar to that observed with the wild-type protein. NQO1 was also inhibited by resveratrol and by nicotinamide. Inhibition of NQO1 by resveratrol was approximately 10,000-fold less strong than that observed with the structurally similar enzyme, NRH quinine oxidoreductase 2 (NQO2). The enzyme exhibited non-cooperative behaviour towards nicotinamide, whereas resveratrol induced modest negative cooperativity (h = 0.85). Nicotinamide stabilized wild-type NQO1 and p.R139W towards thermal denaturation but had no detectable effect on p.P187S. Resveratrol destabilized the wild-type enzyme and both cancer-associated variants. Our data suggest that neither polymorphism exerts its effect by changing the enzyme's ability to exhibit negative cooperativity towards inhibitors. However, it does demonstrate that resveratrol can inhibit NQO1 in addition to this compound's well-documented effects on NQO2. The implications of these findings for molecular pathology are discussed.
Assuntos
Estabilidade Enzimática/efeitos dos fármacos , NAD(P)H Desidrogenase (Quinona)/genética , Neoplasias/genética , Quinona Redutases/genética , Dicumarol/química , Dicumarol/farmacologia , Humanos , Cinética , NAD(P)H Desidrogenase (Quinona)/antagonistas & inibidores , NAD(P)H Desidrogenase (Quinona)/química , Neoplasias/química , Neoplasias/tratamento farmacológico , Neoplasias/enzimologia , Niacinamida/química , Niacinamida/farmacologia , Polimorfismo Genético , Ligação Proteica , Quinona Redutases/antagonistas & inibidores , Quinona Redutases/químicaRESUMO
NAD(P)H quinone oxidoreductase-1 (NQO1) is a homodimeric protein that acts as a detoxifying enzyme or as a chaperone protein. Dicourmarol interacts with NQO1 at the NAD(P)H binding site and can both inhibit enzyme activity and modulate the interaction of NQO1 with other proteins. We show that the binding of dicoumarol and related compounds to NQO1 generates negative cooperativity between the monomers. This does not occur in the presence of the reducing cofactor, NAD(P)H, alone. Alteration of Gly150 (but not Gly149 or Gly174) abolished the dicoumarol-induced negative cooperativity. Analysis of the dynamics of NQO1 with the Gaussian network model indicates a high degree of collective motion by monomers and domains within NQO1. Ligand binding is predicted to alter NQO1 dynamics both proximal to the ligand binding site and remotely, close to the second binding site. Thus, drug-induced modulation of protein motion might contribute to the biological effects of putative inhibitors of NQO1.
Assuntos
Regulação Alostérica/efeitos dos fármacos , Dicumarol/farmacologia , Inibidores Enzimáticos/farmacologia , NAD(P)H Desidrogenase (Quinona)/antagonistas & inibidores , Substituição de Aminoácidos , Domínio Catalítico , Linhagem Celular Tumoral , Dicumarol/metabolismo , Inibidores Enzimáticos/metabolismo , Humanos , Ligantes , NAD(P)H Desidrogenase (Quinona)/genética , NAD(P)H Desidrogenase (Quinona)/metabolismo , Ligação Proteica , Proteína Supressora de Tumor p53/metabolismoRESUMO
NAD(P)H quinone oxidoreductase 1 (NQO1) is a multi-functional protein that catalyses the reduction of quinones (and other molecules), thus playing roles in xenobiotic detoxification and redox balance, and also has roles in stabilising apoptosis regulators such as p53. The structure and enzymology of NQO1 is well-characterised, showing a substituted enzyme mechanism in which NAD(P)H binds first and reduces an FAD cofactor in the active site, assisted by a charge relay system involving Tyr-155 and His-161. Protein dynamics play important role in physio-pathological aspects of this protein. NQO1 is a good target to treat cancer due to its overexpression in cancer cells. A polymorphic form of NQO1 (p.P187S) is associated with increased cancer risk and certain neurological disorders (such as multiple sclerosis and Alzheimer´s disease), possibly due to its roles in the antioxidant defence. p.P187S has greatly reduced FAD affinity and stability, due to destabilization of the flavin binding site and the C-terminal domain, which leading to reduced activity and enhanced degradation. Suppressor mutations partially restore the activity of p.P187S by local stabilization of these regions, and showing long-range allosteric communication within the protein. Consequently, the correction of NQO1 misfolding by pharmacological chaperones is a viable strategy, which may be useful to treat cancer and some neurological conditions, targeting structural spots linked to specific disease-mechanisms. Thus, NQO1 emerges as a good model to investigate loss of function mechanisms in genetic diseases as well as to improve strategies to discriminate between neutral and pathogenic variants in genome-wide sequencing studies.
Assuntos
Doença de Alzheimer/tratamento farmacológico , Chaperonas Moleculares/uso terapêutico , Esclerose Múltipla/tratamento farmacológico , NAD(P)H Desidrogenase (Quinona)/metabolismo , Neoplasias/tratamento farmacológico , Doença de Alzheimer/enzimologia , Doença de Alzheimer/genética , Animais , Flavina-Adenina Dinucleotídeo/genética , Flavina-Adenina Dinucleotídeo/metabolismo , Estudo de Associação Genômica Ampla , Humanos , Esclerose Múltipla/enzimologia , Esclerose Múltipla/genética , NAD(P)H Desidrogenase (Quinona)/genética , Neoplasias/enzimologia , Neoplasias/genética , Neoplasias/patologia , Polimorfismo Genético , Domínios Proteicos , Dobramento de Proteína/efeitos dos fármacos , Proteína Supressora de Tumor p53/genética , Proteína Supressora de Tumor p53/metabolismoRESUMO
In microorganisms and plants, N-acetyl-l-glutamate kinase (NAGK) catalyzes the second step in l-arginine synthesis, the phosphorylation of N-Acetyl-l-glutamate (NAG) to give N-acetyl-l-glutamate-5-phosphate. NAGK is only present in microorganisms and plants but absent in mammals, which makes it an attractive target for antimicrobial or biocidal development. Understanding the substrate binding mode and reaction mechanism of NAGK is crucial for targeting the kinase to develop potential therapies. Here, the substrate binding mode was studied by comparing the conformational change of NAGK in the presence and in the absence of the NAG substrate based on molecular dynamics simulations. We revealed that with substrate binding, the catalytic site of the kinase involving three loops in NAGK exhibits a closed conformation, which is predominantly controlled by an interaction between Arg98 and the α-COO- of NAG. Lys41 is found to guide phosphate transfer through the interactions with the ß-,γ-, and γ-phosphate oxygen atoms of adenosine 5'-triphosphate surrounded by two highly conserved glycine residues (Gly44 and Gly76), while Arg98 helps to position the NAG substrate in the catalytic site, which facilitates the phosphate transfer. Furthermore, we elucidated phosphate-transfer reaction mechanism using hybrid density functional theory-based quantum mechanics/molecular mechanics calculations (B97D/AMBER99) and found that the catalysis follows a dissociative mechanism.
Assuntos
Fosfotransferases (Aceptor do Grupo Carboxila)/química , Teoria Quântica , Modelos Moleculares , Fosforilação , Fosfotransferases (Aceptor do Grupo Carboxila)/metabolismo , Conformação ProteicaRESUMO
Fructose 1,6-bisphosphatase (FBPase) is a key enzyme in gluconeogenesis. It is a potential drug target in the treatment of type II diabetes. The protein is also associated with a rare inherited metabolic disease and some cancer cells lack FBPase activity which promotes glycolysis facilitating the Warburg effect. Thus, there is interest in both inhibiting the enzyme (for diabetes treatment) and restoring its activity (in relevant cancers). The mammalian enzyme is tetrameric, competitively inhibited by Fructose 2,6-bisphosphate and negatively allosterically regulated by AMP. This allosteric regulation requires information transmission between the AMP binding site and the active site of the enzyme. A recent paper by Topaz et al. (Bioscience Reports (2019) 39, pii:BSR20180960) has added additional detail to our understanding of this information transmission process. Two residues in the AMP binding site (Lys112 and Tyr113) were shown to be involved in initiating the message between the two sites. This tyrosine residue has recently be shown to be important with protein's interaction with the antidiabetic drug metformin. A variant designed to increase metal ion affinity (M248D) resulted in a five-fold increase in enzymatic activity. Interestingly alterations of two residues at the subunit interfaces (Tyr164 and Met177) resulted in increased responsiveness to AMP. Overall, these findings may have implications in the design of novel FBPase inhibitors or activators.
Assuntos
Diabetes Mellitus Tipo 2 , Frutose-Bifosfatase , Monofosfato de Adenosina , Animais , Frutose , MutaçãoRESUMO
Mevalonate Kinase (MVK) catalyses the ATP-Mg2+ mediated phosphate transfer of mevalonate to produce mevalonate 5-phosphate and is a key kinase in the mevalonate pathway in the biosynthesis of isopentenyl diphosphate, the precursor of isoprenoid-based biofuels. However, the crystal structure in complex with the native substrate mevalonate, ATP and Mg2+ has not been resolved, which has limited the understanding of its reaction mechanism and therefore its application in the production of isoprenoid-based biofuels. Here using molecular docking, molecular dynamics (MD) simulations and a hybrid QM/MM study, we revisited the location of Mg2+ resolved in the crystal structure of MVK and determined a catalytically competent MVK structure in complex with the native substrate mevalonate and ATP. We demonstrated that significant conformational change on a flexible loop connecting the α6 and α7 helix is induced by the substrate binding. Further, we found that Asp204 is coordinated to the Mg2+ ion. Arg241 plays a crucial role in organizing the triphosphoryl tail of ATP for in-line phosphate transfer and stabilizing the negative charge that accumulates at the ß,γ-bridging oxygen of ATP upon bond cleavage. Remarkably, we revealed that the phosphorylation of mevalonate catalyzed by MVK occurs via a direct phosphorylation mechanism, instead of the conventionally postulated catalytic base mechanism. The catalytically competent complex structure of MVK as well as the mechanism of reaction will pave the way for the rational engineering of MVK to exploit its applications in the production of biofuels.
Assuntos
Ácido Mevalônico/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Trifosfato de Adenosina/química , Trifosfato de Adenosina/metabolismo , Animais , Magnésio/química , Magnésio/metabolismo , Ácido Mevalônico/química , Simulação de Acoplamento Molecular , Fosforilação , Fosfotransferases (Aceptor do Grupo Álcool)/química , Ligação Proteica , Conformação Proteica , Conformação Proteica em alfa-Hélice , Teoria Quântica , RatosRESUMO
NAD(P)H quinone oxidoreductase 1 (NQO1) catalyses the two electron reduction of quinones and a wide range of other organic compounds. Its physiological role is believed to be partly the reduction of free radical load in cells and the detoxification of xenobiotics. It also has non-enzymatic functions stabilising a number of cellular regulators including p53. Functionally, NQO1 is a homodimer with two active sites formed from residues from both polypeptide chains. Catalysis proceeds via a substituted enzyme mechanism involving a tightly bound FAD cofactor. Dicoumarol and some structurally related compounds act as competitive inhibitors of NQO1. There is some evidence for negative cooperativity in quinine oxidoreductases which is most likely to be mediated at least in part by alterations to the mobility of the protein. Human NQO1 is implicated in cancer. It is often over-expressed in cancer cells and as such is considered as a possible drug target. Interestingly, a common polymorphic form of human NQO1, p.P187S, is associated with an increased risk of several forms of cancer. This variant has much lower activity than the wild-type, primarily due to its substantially reduced affinity for FAD which results from lower stability. This lower stability results from inappropriate mobility of key parts of the protein. Thus, NQO1 relies on correct mobility for normal function, but inappropriate mobility results in dysfunction and may cause disease.
Assuntos
Dicumarol/química , Inibidores Enzimáticos/química , Flavina-Adenina Dinucleotídeo/química , NAD(P)H Desidrogenase (Quinona)/química , Neoplasias/enzimologia , Domínio Catalítico , Dicumarol/farmacologia , Inibidores Enzimáticos/farmacologia , Estabilidade Enzimática , Flavina-Adenina Dinucleotídeo/metabolismo , Expressão Gênica , Humanos , Modelos Moleculares , Mutação , NAD(P)H Desidrogenase (Quinona)/genética , NAD(P)H Desidrogenase (Quinona)/metabolismo , Neoplasias/tratamento farmacológico , Neoplasias/genética , Neoplasias/patologia , Ligação Proteica , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , Multimerização ProteicaRESUMO
Despite being one of the most commonly used drugs, the molecular mechanism of action of the anthelmintic praziquantel remains unknown. There are some unusual features of this drug. Critically, widespread resistance to praziquantel has not developed despite decades of use. Here, we set out some challenges in praziquantel research and propose some provocative hypotheses to address these. We suggest that praziquantel may have multiple pharmacologically relevant targets and the effects on these may synergise to produce an overall, detrimental effect on the parasite. Praziquantel also acts on a number of host proteins and we propose that these actions are important in the drug's overall mechanism. Although the drug is largely used in the treatment of human and domestic animal worm infections, there is a considerable "grey literature" along with some academic studies which may have been overlooked. It appears that praziquantel may be effective against hydra. It may also be effective against some unicellular parasites such as Giardia spp. Further, scientific work on these understudied areas may be useful in understanding the molecular mechanism in Trematoda. The lack of widespread resistance suggests that praziquantel may act, at least in part, on a protein-protein interaction. Altered drug metabolism or enhanced drug efflux are the most likely ways resistance may arise. There is a critical need to understand the biochemical pharmacology of this drug in order to inform the discovery of the next generation of anthelmintic drugs.
Assuntos
Anti-Helmínticos/farmacologia , Giardia lamblia/efeitos dos fármacos , Praziquantel/farmacologia , Trematódeos/efeitos dos fármacos , Animais , Anti-Helmínticos/química , Humanos , Testes de Sensibilidade Parasitária , Praziquantel/químicaRESUMO
Galactokinase catalyses the ATP-dependent phosphorylation of galactose. A galactokinase-like sequence was identified in a Fasciola hepatica EST library. Recombinant expression of the corresponding protein in Escherichia coli resulted in a protein of approximately 50â¯kDa. The protein is monomeric, like galactokinases from higher animals, yeasts and some bacteria. The protein has no detectable enzymatic activity with galactose or N-acetylgalactosamine as a substrate. However, it does bind to ATP. Molecular modelling predicted that the protein adopts a similar fold to galactokinase and other GHMP kinases. However, a key loop in the active site was identified which may influence the lack of activity. Sequence analysis strongly suggested that this protein (and other proteins annotated as "galactokinase" in the trematodes Schistosoma mansoni and Clonorchis sinensis) are closer to N-acetylgalactosamine kinases. No other galactokinase-like sequences appear to be present in the genomes of these three species. This raises the intriguing possibility that these (and possibly other) trematodes are unable to catabolise galactose through the Leloir pathway due to the lack of a functional galactokinase.
Assuntos
Fasciola hepatica/enzimologia , Galactoquinase/metabolismo , Galactose/metabolismo , Trifosfato de Adenosina/química , Trifosfato de Adenosina/metabolismo , Animais , Sequência de Bases , Cromatografia em Gel , Eletroforese em Gel de Poliacrilamida , Fluorometria , Galactoquinase/genética , Galactoquinase/isolamento & purificação , Galactose/química , Modelos Moleculares , Fosforilação , Filogenia , Proteínas Recombinantes/metabolismo , Alinhamento de SequênciaRESUMO
Schistosoma mansoni, like other trematodes, expresses a number of unusual calcium binding proteins which consist of an EF-hand domain joined to a dynein light chain-like (DLC-like) domain by a flexible linker. These proteins have been implicated in host immune responses and drug binding. Three members of this protein family from S. mansoni (SmTAL1, SmTAL2 and SmTAL3) have been well characterised biochemically. Here we characterise the remaining family members from this species (SmTAL4-13). All of these proteins form homodimers and all except SmTAL5 bind to calcium and manganese ions. SmTAL9, 10 and 11 also bind to magnesium ions. The antischistosomal drug, praziquantel interacts with SmTAL4, 5 and 8. Some family members also bind to calmodulin antagonists such as chlorpromazine and trifluoperazine. Molecular modelling suggests that all ten proteins adopt similar overall folds with the EF-hand and DLC-like domains folding discretely. Bioinformatics analyses suggest that the proteins may fall into two main categories: (i) those which bind calcium ions reversibly at the second EF-hand and may play a role in signalling (SmTAL1, 2, 8 and 12) and (ii) those which bind calcium ions at the first EF-hand and may play either signalling or structural roles (SmTAL7, 9, 10 and 13). The remaining proteins include those which do not bind calcium ions (SmTAL3 and 5) and three other proteins (SmTAL4, 6 and 11). The roles of these proteins are less clear, but they may also have structural roles.
Assuntos
Alérgenos/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Proteínas de Helminto/metabolismo , Schistosoma mansoni/química , Alérgenos/química , Animais , Anti-Helmínticos/metabolismo , Cálcio/metabolismo , Proteínas de Ligação ao Cálcio/química , Cátions Bivalentes/metabolismo , Clorpromazina/metabolismo , Proteínas de Helminto/química , Manganês/metabolismo , Modelos Moleculares , Praziquantel/metabolismo , Ligação Proteica , Conformação Proteica , Dobramento de Proteína , Multimerização Proteica , Trifluoperazina/metabolismoRESUMO
Mutations causing single amino acid exchanges can dramatically affect protein stability and function, leading to disease. In this chapter, we will focus on several representative cases in which such mutations affect protein stability and function leading to cancer. Mutations in BRAF and p53 have been extensively characterized as paradigms of loss-of-function/gain-of-function mechanisms found in a remarkably large fraction of tumours. Loss of RB1 is strongly associated with cancer progression, although the molecular mechanisms by which missense mutations affect protein function and stability are not well known. Polymorphisms in NQO1 represent a remarkable example of the relationships between intracellular destabilization and inactivation due to dynamic alterations in protein ensembles leading to loss of function. We will review the function of these proteins and their dysfunction in cancer and then describe in some detail the effects of the most relevant cancer-associated single amino exchanges using a translational perspective, from the viewpoints of molecular genetics and pathology, protein biochemistry and biophysics, structural, and cell biology. This will allow us to introduce several representative examples of natural and synthetic small molecules applied and developed to overcome functional, stability, and regulatory alterations due to cancer-associated amino acid exchanges, which hold the promise for using them as potential pharmacological cancer therapies.
Assuntos
Chaperonas Moleculares/farmacologia , Neoplasias/tratamento farmacológico , Animais , Descoberta de Drogas , Humanos , Chaperonas Moleculares/uso terapêutico , Mutação , NAD(P)H Desidrogenase (Quinona)/antagonistas & inibidores , NAD(P)H Desidrogenase (Quinona)/química , NAD(P)H Desidrogenase (Quinona)/genética , Dobramento de Proteína , Estabilidade Proteica , Proteínas Proto-Oncogênicas B-raf/genética , Proteínas Proto-Oncogênicas B-raf/fisiologia , Proteína Supressora de Tumor p53/genética , Proteína Supressora de Tumor p53/fisiologiaRESUMO
Human proteins are vulnerable towards disease-associated single amino acid replacements affecting protein stability and function. Interestingly, a few studies have shown that consensus amino acids from mammals or vertebrates can enhance protein stability when incorporated into human proteins. Here, we investigate yet unexplored relationships between the high vulnerability of human proteins towards disease-associated inactivation and recent evolutionary site-specific divergence of stabilizing amino acids. Using phylogenetic, structural and experimental analyses, we show that divergence from the consensus amino acids at several sites during mammalian evolution has caused local protein destabilization in two human proteins linked to disease: cancer-associated NQO1 and alanine:glyoxylate aminotransferase, mutated in primary hyperoxaluria type I. We demonstrate that a single consensus mutation (H80R) acts as a disease suppressor on the most common cancer-associated polymorphism in NQO1 (P187S). The H80R mutation reactivates P187S by enhancing FAD binding affinity through local and dynamic stabilization of its binding site. Furthermore, we show how a second suppressor mutation (E247Q) cooperates with H80R in protecting the P187S polymorphism towards inactivation through long-range allosteric communication within the structural ensemble of the protein. Our results support that recent divergence of consensus amino acids may have occurred with neutral effects on many functional and regulatory traits of wild-type human proteins. However, divergence at certain sites may have increased the propensity of some human proteins towards inactivation due to disease-associated mutations and polymorphisms. Consensus mutations also emerge as a potential strategy to identify structural hot-spots in proteins as targets for pharmacological rescue in loss-of-function genetic diseases.
Assuntos
Angiotensinogênio/genética , Proteínas/genética , Alanina/genética , Alanina Transaminase/genética , Alanina Transaminase/metabolismo , Aminoácidos/genética , Angiotensinogênio/metabolismo , Animais , Sítios de Ligação , Sequência Consenso/genética , Evolução Molecular , Humanos , Mutação , NAD(P)H Desidrogenase (Quinona)/genética , NAD(P)H Desidrogenase (Quinona)/metabolismo , Filogenia , Polimorfismo Genético , Ligação Proteica , Estabilidade Proteica , Proteínas/metabolismo , Transaminases/genética , Transaminases/metabolismoRESUMO
Eppin is a serine protease inhibitor expressed in male reproductive tissues.The aim of this study was to investigate the localisation and regulation of eppin expression in myeloid and epithelial cell lines, and explore its potential role as a multifunctional host defence protein.Using immunohistochemistry and Western blotting, eppin was detected in the lungs of patients with acute respiratory distress syndrome and cystic fibrosis lung disease. Expression of eppin in monocytic cells was unaffected by stimulation with Toll-like receptor agonists, cytokines and hormone receptor agonists. However, upregulated expression and secretion of eppin was observed following treatment of monocytes with epidermal growth factor. Incubation of recombinant eppin with monocytic cells resulted in significant inhibition of lipopolysaccharide-induced chemokine production. Furthermore, eppin inhibited lipopolysaccharide-induced NF-κB activation by a mechanism which involved accumulation of phosphorylated IκBα. In an in vivo model of lung inflammation induced by lipopolysaccharide, eppin administration resulted in decreased recruitment of neutrophils to the lung with a concomitant reduction in the levels of the neutrophil chemokine macrophage inflammatory protein-2.Overall, these results suggest a role for eppin outside of the reproductive tract and that eppin may have a role in the innate immune response in the lung.