RESUMO
Pyridoxal kinase (PdxK) is a vitamin B6 salvage pathway enzyme which produces pyridoxal phosphate. We have investigated the impact of PdxK deletion in Leishmania donovani on parasite survivability, infectivity and cellular metabolism. LdPdxK mutants were generated by gene replacement strategy. All mutants showed significant reduction in growth in comparison to wild type. For PdxK mediated biochemical perturbations, only heterozygous mutants and complementation mutants were used as the growth of null mutants were compromised. Heterozygous mutant showed reduction invitro infectivity and higher cytosolic and mitochondrial ROS levels. Glutathione levels decreased significantly in heterozygous mutant indicating its involvement in cellular oxidative metabolism. Pyridoxal kinase gene deletion resulted in reduced ATP levels in parasites and arrest at G0/G1 phase of cell cycle. All these perturbations were rescued by PdxK gene complementation. This is the first report to confirm that LdPdxK plays an indispensable role in cell survival, pathogenicity, redox metabolism and cell cycle progression of L. donovani parasites. These results provide substantial evidence supporting PdxK as a therapeutic target for the development of specific antileishmanial drug candidates.
Assuntos
Pontos de Checagem do Ciclo Celular , Deleção de Genes , Leishmania donovani , Oxirredução , Piridoxal Quinase , Leishmania donovani/genética , Leishmania donovani/metabolismo , Leishmania donovani/crescimento & desenvolvimento , Piridoxal Quinase/metabolismo , Piridoxal Quinase/genética , Pontos de Checagem do Ciclo Celular/genética , Animais , Proteínas de Protozoários/genética , Proteínas de Protozoários/metabolismo , Espécies Reativas de Oxigênio/metabolismo , CamundongosRESUMO
Pyridoxal kinase (PDXK) is an essential enzyme in the synthesis of pyridoxal 5-phosphate (PLP), the active form of vitamin B6, which plays a pivotal role in maintaining the enzyme activity necessary for cell metabolism. Thus, PDXK has garnered attention as a potential target for metabolism regulation and tumor therapy. Despite this interest, existing PDXK inhibitors have faced limitations, including weak suppressive activity, unclear mechanisms of action, and associated toxic side effects. In this study, we present the discovery of a novel PDXK inhibitor, luteolin, through a high-throughput screening approach based on enzyme activity. Luteolin, a natural product, exhibits micromolar-level affinity for PDXK and effectively inhibits the enzyme's activity in vitro. Our crystal structures reveal that luteolin occupies the ATP binding pocket through hydrophobic interactions and a weak hydrogen bonding pattern, displaying reversible characteristics as confirmed by biochemical assays. Moreover, luteolin disrupts vitamin B6 metabolism by targeting PDXK, thereby inhibiting the proliferation of leukemia cells. This research introduces a novel screening method for identifying high-affinity and potent PDXK inhibitors and sheds light on clarification of the structural mechanism of PDXK-luteolin for subsequent structure optimization of inhibitors.
Assuntos
Luteolina , Piridoxal Quinase , Humanos , Piridoxal Quinase/química , Piridoxal Quinase/metabolismo , Luteolina/farmacologia , Fosfato de Piridoxal/metabolismo , Vitamina B 6/farmacologia , Vitamina B 6/metabolismo , Inibidores de Proteínas Quinases/farmacologiaRESUMO
Pyridoxal 5'-phosphate (PLP), an essential cofactor for multiple enzymes, was used as a protein decoy to prompt enzyme expression and activity for the first time. The best chassis, denoted as WJK, was developed using a pyridoxal kinase (PdxK) and integrated at the HK022 phage attack site of Escherichia coli W3110. When compared with the original strain, the amount and activity of lysine decarboxylase (CadA) in WJK were significantly increased by 100 % and 120 %, respectively. When supplementary nineteen amino acids as second carbon source, cell growth and protein trade-off were observed. The transcriptional levels of genes from glycolysis to TCA cycle, adhE, argH and gdhA were dominating and redirected more flux into α-ketoglutarate, thus facilitated cell growth. Stepwise improvement was conducted with pyridoxal and nitrogen-rich medium; hence, CadA activity was increased to 60 g-cadaverine/g-dry cell weight/h. By reutilizing the whole-cell biocatalysts in two repeated reactions with the supplementation of fresh cells, a total cadaverine of 576 g/L was obtained even without additional PLP. Notably, PLP decoy augment the enzymatic activities of 5-aminolevulinic acid synthase and glutamate/lysine/arginine decarboxylases by over 100 %. Finally, a conserved PLP-binding pocket, Ser-His-Lys, was identified as a vital PLP sponge site that simultaneously improved protein quality and quantity.
Assuntos
Escherichia coli , Engenharia Metabólica , Fosfato de Piridoxal , Escherichia coli/metabolismo , Fosfato de Piridoxal/metabolismo , Carboxiliases/metabolismo , Transformação Genética , Cadaverina/metabolismo , Piridoxal Quinase/metabolismo , Engenharia Metabólica/métodosRESUMO
Human parasites cause several diseased conditions with high morbidity and mortality in a large section of the population residing in various geographical areas. Nearly three billion people suffer from either one or many parasitic infections globally, with almost one million deaths annually. In spite of extensive research and advancement in the medical field, no effective vaccine is available against prominent human parasitic diseases that necessitate identification of novel targets for designing specific inhibitors. Vitamin B6 is an important ubiquitous co-enzyme that participates in several biological processes and plays an important role in scavenging ROS (reactive oxygen species) along with providing resistance to oxidative stress. Moreover, the absence of the de novo vitamin B6 biosynthetic pathway in human parasites makes this pathway indispensable for the survival of these pathogens. Pyridoxal kinase (PdxK) is a crucial enzyme for vitamin B6 salvage pathway and participates in the process of vitamers B6 phosphorylation. Since the parasites are dependent on pyridoxal kinase for their survival and infectivity to the respective hosts, it is considered a promising candidate for drug discovery. The detailed structural analysis of PdxK from disease-causing parasites has provided insights into the catalytic mechanism of this enzyme as well as significant differences from their human counterpart. Simultaneously, structure-based studies have identified small lead molecules that can be exploited for drug discovery against protozoan parasites. The present review provides structural and functional highlights of pyridoxal kinase for its implication in developing novel and potent therapeutics to combat fatal parasitic diseases.
Assuntos
Parasitos , Piridoxal Quinase , Animais , Descoberta de Drogas , Humanos , Parasitos/metabolismo , Piridoxal Quinase/química , Piridoxal Quinase/genética , Piridoxal Quinase/metabolismo , Piridoxina/metabolismo , Vitamina B 6/química , Vitamina B 6/metabolismo , Vitamina B 6/farmacologiaRESUMO
Vitamins B1 (thiamine) and B6 (pyridox (al/ine/amine)) are crucial for central nervous system (CNS) function and neurogenesis due to the coenzyme action of their phosphorylated derivatives in the brain metabolism of glucose and neurotransmitters. Here, the non-coenzyme action of thiamine on the major mammalian producers of pyridoxal-5'-phosphate (PLP), such as pyridoxal kinase (PdxK) and pyridoxine 5'-phosphate oxidase (PNPO), is characterized. Among the natural thiamine compounds, thiamine triphosphate (ThTP) is the best effector of recombinant human PdxK (hPdxK) in vitro, inhibiting hPdxK in the presence of Mg2+ but activating the Zn2+ -dependent reaction. Inhibition of hPdxK by thiamine antagonists decreases from amprolium to pyrithiamine to oxythiamine, highlighting possible dysregulation of both the B1 - and B6 -dependent metabolism in the chemical models of thiamine deficiency. Compared with the canonical hPdxK, the D87H and V128I variants show a twofold increase in Kapp of thiamine inhibition, and the V128I and H246Q variants show a fourfold and a twofold decreased Kapp of thiamine diphosphate (ThDP), respectively. Thiamine administration changes diurnal regulation of PdxK activity and phosphorylation at Ser213 and Ser285, expression of the PdxK-related circadian kinases/phosphatases in the rat brain, and electrocardiography (ECG). In contrast to PdxK, PNPO is not affected by thiamine or its derivatives, either in vitro or in vivo. Dephosphorylation of the PdxK Ser285, potentially affecting mobility of the ATP-binding loop, inversely correlates with the enzyme activity. Dephosphorylation of the PdxK Ser213, which is far away from the active site, does not correlate with the activity. The correlations analysis suggests the PdxK Ser213 to be a target of kinase MAP2K1 and phosphatase Ppp1ca. Diurnal effects of thiamine administration on the metabolically linked ThDP- and PLP-dependent enzymes may support the brain homeostatic mechanisms and physiological fitness.
Assuntos
Piridoxal Quinase , Tiamina , Animais , Encéfalo/metabolismo , Mamíferos/metabolismo , Fosfatos , Piridoxal Quinase/química , Piridoxal Quinase/metabolismo , Fosfato de Piridoxal/metabolismo , Fosfato de Piridoxal/farmacologia , Ratos , Tiamina/farmacologiaRESUMO
Pyridoxal 5'-phosphate (PLP), the active form of vitamin B6, serves as a cofactor for scores of B6-dependent (PLP-dependent) enzymes involved in many cellular processes. One such B6 enzyme is dopa decarboxylase (DDC), which is required for the biosynthesis of key neurotransmitters, e.g., dopamine and serotonin. PLP-dependent enzymes are biosynthesized as apo-B6 enzymes and then converted to the catalytically active holo-B6 enzymes by Schiff base formation between the aldehyde of PLP and an active site lysine of the protein. In eukaryotes, PLP is made available to the B6 enzymes through the activity of the B6-salvage enzymes, pyridoxine 5'-phosphate oxidase (PNPO) and pyridoxal kinase (PLK). To minimize toxicity, the cell keeps the content of free PLP (unbound) very low through dephosphorylation and PLP feedback inhibition of PNPO and PLK. This has led to a proposed mechanism of complex formation between the B6-salvage enzymes and apo-B6 enzymes prior to the transfer of PLP, although such complexes are yet to be characterized at the atomic level, presumably due to their transient nature. A computational study, for the first time, was used to predict a likely PNPO and DDC complex, which suggested contact between the allosteric PLP tight-binding site on PNPO and the active site of DDC. Using isothermal calorimetry and/or surface plasmon resonance, we also show that PNPO binds both apoDDC and holoDDC with dissociation constants of 0.93 ± 0.07 µM and 2.59 ± 0.11 µM, respectively. Finally, in the presence of apoDDC, the tightly bound PLP on PNPO is transferred to apoDDC, resulting in the formation of about 35% holoDDC.
Assuntos
Piridoxaminafosfato Oxidase , Piridoxina , Piridoxaminafosfato Oxidase/metabolismo , Dopa Descarboxilase , Fosfato de Piridoxal/metabolismo , Oxirredutases , Piridoxal Quinase/metabolismoRESUMO
The antimalarial artemisinins have also been implicated in the regulation of various cellular pathways including immunomodulation of cancers and regulation of pancreatic cell signaling in mammals. Despite their widespread application, the cellular specificities and molecular mechanisms of target recognition by artemisinins remain poorly characterized. We recently demonstrated how these drugs modulate inhibitory postsynaptic signaling by direct binding to the postsynaptic scaffolding protein gephyrin. Here, we report the crystal structure of the central metabolic enzyme pyridoxal kinase (PDXK), which catalyzes the production of the active form of vitamin B6 (also known as pyridoxal 5'-phosphate [PLP]), in complex with artesunate at 2.4-Šresolution. Partially overlapping binding of artemisinins with the substrate pyridoxal inhibits PLP biosynthesis as demonstrated by kinetic measurements. Electrophysiological recordings from hippocampal slices and activity measurements of glutamic acid decarboxylase (GAD), a PLP-dependent enzyme synthesizing the neurotransmitter γ-aminobutyric acid (GABA), define how artemisinins also interfere presynaptically with GABAergic signaling. Our data provide a comprehensive picture of artemisinin-induced effects on inhibitory signaling in the brain.
Assuntos
Artemisininas/farmacologia , Regulação para Baixo , Inibição Neural/efeitos dos fármacos , Inibidores de Proteínas Quinases/farmacologia , Piridoxal Quinase/antagonistas & inibidores , Transmissão Sináptica/efeitos dos fármacos , Trifosfato de Adenosina/análogos & derivados , Trifosfato de Adenosina/metabolismo , Animais , Artemisininas/química , Sítios de Ligação , Regulação para Baixo/efeitos dos fármacos , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Feminino , Neurônios GABAérgicos/efeitos dos fármacos , Neurônios GABAérgicos/metabolismo , Glutamato Descarboxilase/metabolismo , Masculino , Camundongos Endogâmicos C57BL , Modelos Biológicos , Modelos Moleculares , Inibidores de Proteínas Quinases/química , Piridoxal Quinase/química , Piridoxal Quinase/metabolismo , Sinapses/efeitos dos fármacos , Sinapses/metabolismo , Ácido gama-Aminobutírico/biossínteseRESUMO
Pyridoxal kinases (PLK) are crucial enzymes for the biosynthesis of pyridoxal phosphate, an important cofactor in a plethora of enzymatic reactions. The evolution of these enzymes resulted in different catalytic designs. In addition to the active site, the importance of a cysteine, embedded within a distant flexible lid region, was recently demonstrated. This cysteine forms a hemithioacetal with the pyridoxal aldehyde and is essential for catalysis. Despite the prevalence of these enzymes in various organisms, no tools were yet available to study the relevance of this lid residue. Here, we introduce pyridoxal probes, each equipped with an electrophilic trapping group in place of the aldehyde to target PLK reactive lid cysteines as a mimic of hemithioacetal formation. The addition of alkyne handles placed at two different positions within the pyridoxal structure facilitates enrichment of PLKs from living cells. Interestingly, depending on the position, the probes displayed a preference for either Gram-positive or Gram-negative PLK enrichment. By applying the cofactor traps, we were able to validate not only previously investigated Staphylococcus aureus and Enterococcus faecalis PLKs but also Escherichia coli and Pseudomonas aeruginosa PLKs, unravelling a crucial role of the lid cysteine for catalysis. Overall, our tailored probes facilitated a reliable readout of lid cysteine containing PLKs, qualifying them as chemical tools for mining further diverse proteomes for this important enzyme class.
Assuntos
Acetais/química , Piridoxal Quinase/metabolismo , Catálise , Cisteína/metabolismo , Bactérias Gram-Negativas/enzimologia , Bactérias Gram-Positivas/enzimologiaRESUMO
Pyridoxal 5'-phosphate (PLP) is the active form of vitamin B6 and a cofactor for more than 140 enzymes. This coenzyme plays a pivotal role in catalysis of various enzymatic reactions that are critical for the survival of organisms. Entamoeba histolytica depends on the uptake of pyridoxal (PL), a B6 vitamer from the external environment which is then phosphorylated by pyridoxal kinase (EhPLK) to form PLP via the salvage pathway. E. histolytica cannot synthesise vitamin B6de-novo, and also lacks pyridoxine 5'-phosphate oxidase, a salvage pathway enzyme required to produce PLP from pyridoxine phosphate (PNP) and pyridoxamine phosphate (PMP). Analysing the importance of PLK in E. histolytica, we have determined the high-resolution crystal structures of the dimeric pyridoxal kinase in apo, ADP-bound, and PLP-bound states. These structures provided a snapshot of the transition state and help in understanding the reaction mechanism in greater detail. The EhPLK structure significantly differed from the human homologue at its PLP binding site, and the phylogenetic study also revealed its divergence from human PLK. Further, gene regulation of EhPLK using sense and antisense RNA showed that any change in optimal level is harmful to the pathogen. Biochemical and in vivo studies unveiled EhPLK to be essential for this pathogen, while the molecular differences with human PLK structure can be exploited for the structure-guided design of EhPLK inhibitors.
Assuntos
Entamoeba histolytica/metabolismo , Piridoxal Quinase/metabolismo , Sítios de Ligação/fisiologia , Catálise , Fosforilação/fisiologia , Filogenia , Fosfato de Piridoxal/análogos & derivados , Fosfato de Piridoxal/metabolismo , Piridoxamina/análogos & derivados , Piridoxamina/metabolismo , Piridoxaminafosfato Oxidase/metabolismo , Vitamina B 6/metabolismoRESUMO
PDXK encodes for a pyridoxal kinase, which converts inactive B6 vitamers to the active cofactor pyridoxal 5'-phosphate (PLP). Recently, biallelic pathogenic variants in PDXK were shown to cause axonal Charcot-Marie-Tooth disease with optic atrophy that responds to PLP supplementation. We present two affected siblings carrying a novel biallelic missense PDXK variant with a similar phenotype with earlier onset. After detection of a novel PDXK variant using Whole Exome Sequencing, we confirmed pathogenicity through in silico protein structure analysis, determination of pyridoxal kinase activity using liquid chromatography-tandem mass spectrometry, and measurement of plasma PLP concentrations using high performance liquid chromatography. Our in silico analysis shows a potential effect on PDXK dimer stability, as well as a putative effect on posttranslational ubiquitination that is predicted to lead to increased protein degradation. We demonstrate that the variant leads to almost complete loss of PDXK enzymatic activity and low PLP levels. Our patients' early diagnosis and prompt PLP replacement restored the PLP plasma levels, enabling long-term monitoring of clinical outcomes. We recommend that patients presenting with similar phenotype should be screened for PDXK mutations, as this is a rare opportunity for treatment.
Assuntos
Atrofia Óptica/tratamento farmacológico , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Polineuropatias/tratamento farmacológico , Fosfato de Piridoxal/uso terapêutico , Vitamina B 6/metabolismo , Adolescente , Feminino , Humanos , Masculino , Mutação , Piridoxal Quinase/metabolismoRESUMO
The enzyme pyridoxal kinase (PdxK) catalyzes the conversion of pyridoxal to pyridoxal-5'-phosphate (PLP) using ATP as the co-factor. The product pyridoxal-5'-phosphate plays a key role in several biological processes such as transamination, decarboxylation and deamination. In the present study, full-length ORF of PdxK from Leishmania donovani (LdPdxK) was cloned and then purified using affinity chromatography. LdPdxK exists as a homo-dimer in solution and shows more activity at near to physiological pH. Biochemical analysis of LdPdxK with pyridoxal, pyridoxamine, pyridoxine and ginkgotoxin revealed its affinity preference towards different substrates. The secondary structure analysis using circular dichroism spectroscopy showed LdPdxK to be predominantly α-helical in organization which tends to decline at lower and higher pH. Simultaneously, LdPdxK was crystallized and its three-dimensional structure in complex with ADP and different substrates were determined. Crystal structure of LdPdxK delineated that it has a central core of ß-sheets surrounded by α-helices with a conserved GTGD ribokinase motif. The structures of LdPdxK disclosed no major structural changes between ADP and ADP- substrate bound structures. In addition, comparative structural analysis highlighted the key differences between the active site pockets of leishmanial and human PdxK, rendering LdPdxK an attractive candidate for the designing of novel and specific inhibitors.
Assuntos
Leishmania donovani/metabolismo , Piridoxal Quinase/química , Piridoxal Quinase/metabolismo , Especificidade por Substrato/fisiologia , Sequência de Aminoácidos , Domínio Catalítico/fisiologia , Humanos , Fosfotransferases (Aceptor do Grupo Álcool)/química , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Conformação Proteica , Fosfato de Piridoxal/química , Fosfato de Piridoxal/metabolismo , Piridoxamina/química , Piridoxamina/metabolismo , Piridoxina/análogos & derivados , Piridoxina/química , Piridoxina/metabolismoRESUMO
Pyridoxine/pyridoxamine 5'-phosphate oxidase (PNPO) and pyridoxal kinase (PDXK) cooperate to produce pyridoxal 5'-phosphate (PLP), the active form of vitamin B6. PDXK phosphorylates pyridoxine, pyridoxamine, and pyridoxal by producing PNP, PMP, and PLP, whereas PNPO oxidizes PNP, PMP, into PLP. We previously demonstrated that PDXK depletion in Drosophila and human cells impacts on glucose metabolism and DNA integrity. Here we characterized sgll, the Drosophila ortholog of PNPO gene, showing that its silencing by RNA interference elicits chromosome aberrations (CABs) in brains and induces diabetic hallmarks such as hyperglycemia and small body size. We showed that in sgllRNAi neuroblasts CABs are largely produced by the genotoxic effect of the advanced glycation end products triggered by high glucose. As in sgllRNAi cells, part of PLP is still produced by PDXK activity, these data suggest that PLP dosage need to be tightly regulated to guarantee glucose homeostasis and DNA integrity.
Assuntos
Drosophila melanogaster/metabolismo , Piridoxal Quinase/metabolismo , Fosfato de Piridoxal/biossíntese , Piridoxaminafosfato Oxidase/metabolismo , Animais , Aberrações Cromossômicas , DNA/fisiologia , Glucose/metabolismo , Produtos Finais de Glicação Avançada/metabolismo , Hiperglicemia/genética , Modelos Animais , Piridoxaminafosfato Oxidase/genética , Interferência de RNA , RNA Interferente Pequeno/genéticaRESUMO
In eukaryotes, pyridoxal kinase (PDXK) acts in vitamin B6 salvage pathway to produce pyridoxal 5'-phosphate (PLP), the active form of the vitamin, which is implicated in numerous crucial metabolic reactions. In Drosophila, mutations in the dPdxk gene cause chromosome aberrations (CABs) and increase glucose content in larval hemolymph. Both phenotypes are rescued by the expression of the wild type human PDXK counterpart. Here we expressed, in dPdxk1 mutant flies, four PDXK human variants: three (D87H, V128I and H246Q) listed in databases, and one (A243G) found in a genetic screening in patients with diabetes. Differently from human wild type PDXK, none of the variants was able to completely rescue CABs and glucose content elicited by dPdxk1 mutation. Biochemical analysis of D87H, V128I, H246Q and A243G proteins revealed reduced catalytic activity and/or reduced affinity for PLP precursors which justify this behavior. Although these variants are rare in population and carried in heterozygous condition, our findings suggest that in certain metabolic contexts and diseases in which PLP levels are reduced, the presence of these PDXK variants could threaten genome integrity and increase cancer risk.
Assuntos
Drosophila/genética , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Piridoxal Quinase/genética , Fosfato de Piridoxal/genética , Animais , Animais Geneticamente Modificados/genética , Aberrações Cromossômicas , Drosophila/metabolismo , Regulação Enzimológica da Expressão Gênica/genética , Instabilidade Genômica , Glucose/metabolismo , Hemolinfa/metabolismo , Humanos , Larva/genética , Larva/metabolismo , Redes e Vias Metabólicas/genética , Mutação/genética , Piridoxal Quinase/metabolismo , Fosfato de Piridoxal/biossíntese , Vitamina B 6/biossíntese , Vitamina B 6/genéticaRESUMO
Expression profiling for genes involved in Vitamin B6 (VitB6) biosynthesis was undertaken to delineate the involvement of de novo and salvage pathway induced by Bacillus subtilis CBR05 against, Xanthomonas campestris pv. vesicatoria in tomato. Pyridoxine biosynthesis (PDX) genes such as PDX1.2 and PDX1.3, were found to be overexpressed significantly at 72 hpi in B. subtilis and pyridoxine inoculated plants. Most significant upregulation was observed in the transcript profile of PDX1.3, which showed more than 12- fold increase in expression. Unfortunately, salt sensitive overlay4 (SOS4) profiling showed irregular expression which corroborates that SOS4 role in VitB6 biosynthesis needs further studies for deciphering a clear notion about their role in tomato. Antioxidant enzymes i.e., superoxide dismutase, catalase, polyphenol oxidase, and peroxidase activities clearly demonstrate escalation till 48 hpi and gets reduced in 72 hpi. Pot trials also confirm that B. subtilis compared to pyridoxine supplementation alone show plant disease resistance and elongated roots. The present study confirms that B. subtilis, as a versatile agent in eliciting induced systemic resistance regulated by de novo pathway as a model for plant defense against X. campestris pv. vesicatoria substantiated by VitB6 biosynthesis. Nevertheless, the study is preliminary and needs further evidence for affirming this phenomenon.
Assuntos
Vias Biossintéticas/genética , Resistência à Doença/genética , Doenças das Plantas/genética , Solanum lycopersicum/genética , Vitamina B 6/biossíntese , Antibiose , Bacillus subtilis/fisiologia , Carbono-Nitrogênio Liases/genética , Carbono-Nitrogênio Liases/metabolismo , Regulação da Expressão Gênica de Plantas , Interações Hospedeiro-Patógeno , Solanum lycopersicum/metabolismo , Solanum lycopersicum/microbiologia , Doenças das Plantas/microbiologia , Folhas de Planta/genética , Folhas de Planta/metabolismo , Folhas de Planta/microbiologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Raízes de Plantas/genética , Raízes de Plantas/metabolismo , Raízes de Plantas/microbiologia , Piridoxal Quinase/genética , Piridoxal Quinase/metabolismo , Xanthomonas vesicatoria/fisiologiaRESUMO
Pyridoxal kinase (PdxK, EC 2.7.1.35) is an important enzyme of vitamin B6 salvage pathway which is required for phosphorylation of B6 vitamers. In the present study, pyridoxal kinase (pdxK) gene from Leishmania donovani (LdPdxK) was cloned and a 33â¯kDa protein was expressed and kinetically characterized. Site-directed mutagenesis was performed to determine the functional significance of conserved GXGD motif. Mutation of Thr229 to Ala did not affect the catalytic function of LdPdxK however Gly228, Gly230 and Asp231 were found to be indispensible for enzyme activity. To determine the role of LdPdxK in Leishmania promastigotes, LdPdxK overexpressing parasites were generated by episomal expression of the enzyme. The overexpression studies revealed the role of this enzyme in growth and infection of the parasite. In silico analysis of the human and parasite PdxK structure revealed significant differences in the active site region thus highlighting its potential as an antileishmanial drug target. Homology model of LdPdxK was built and was subjected to molecular dynamics simulations. Based on the above information, a pharmacophore was developed and shape based virtual screening was performed to identify potential and selective inhibitors against this essential enzyme. The current data suggests that LdPdxK could be a promising antileishmanial drug target.
Assuntos
Piridoxal Quinase/química , Piridoxal Quinase/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Domínio Catalítico , Ativação Enzimática , Expressão Gênica , Humanos , Leishmania donovani/classificação , Leishmania donovani/genética , Leishmania donovani/metabolismo , Redes e Vias Metabólicas , Modelos Moleculares , Mutação , Filogenia , Conformação Proteica , Piridoxal Quinase/genética , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Análise de Sequência de DNA , Vitamina B 6/química , Vitamina B 6/metabolismoRESUMO
The root tip zone is regarded as the principal action site for iron (Fe) toxicity and is more sensitive than other root zones, but the mechanism underpinning this remains largely unknown. We explored the mechanism underpinning the higher sensitivity at the Arabidopsis root tip and elucidated the role of nitric oxide (NO) using NO-related mutants and pharmacological methods. Higher Fe sensitivity of the root tip is associated with reduced potassium (K+ ) retention. NO in root tips is increased significantly above levels elsewhere in the root and is involved in the arrest of primary root tip zone growth under excess Fe, at least in part related to NO-induced K+ loss via SNO1 (sensitive to nitric oxide 1)/SOS4 (salt overly sensitive 4) and reduced root tip zone cell viability. Moreover, ethylene can antagonize excess Fe-inhibited root growth and K+ efflux, in part by the control of root tip NO levels. We conclude that excess Fe attenuates root growth by effecting an increase in root tip zone NO, and that this attenuation is related to NO-mediated alterations in K+ homeostasis, partly via SNO1/SOS4.
Assuntos
Arabidopsis/metabolismo , Ferro/metabolismo , Óxido Nítrico/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Potássio/metabolismo , Arabidopsis/efeitos dos fármacos , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Morte Celular , Etilenos/metabolismo , Homeostase/efeitos dos fármacos , Ferro/toxicidade , Raízes de Plantas/citologia , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/metabolismo , Plantas Geneticamente Modificadas , Piridoxal Quinase/genética , Piridoxal Quinase/metabolismo , Estresse Fisiológico/efeitos dos fármacosRESUMO
Cadaverine, a five-carbon diamine (1,5-diaminopentane), can be made by fermentation or direct bioconversion and plays an important role as a building block of polyamides. Lysine decarboxylase (CadA) transforms L-lysine to cadaverine and pyridoxal 5'-phosphate (PLP) can increases conversion rate and yield as a cofactor. Biotransformation of cadaverine using whole Escherichia coli cells that overexpress the lysine decarboxylase has many merits, such as the rapid conversion of l-lysine to cadaverine, possible application of high concentration reactions up to the molar level, production of less byproduct and potential reuse of the enzyme by immobilization. However, the supply of PLP, which is a cofactor of lysine decarboxylase, is the major bottleneck in this system. Therefore, we initiated our study on PLP precursors and PLP-related enzymes and discovered that pyridoxal (PL) can be a viable alternative to supply PLP. Among various PLP systems examined, pyridoxal kinase (PdxY) showed the highest conversion of PL to PLP, resulting in more than 60% conversion of l-lysine to cadaverine with lysine decarboxylase. When the reaction with 0.4M l-lysine, 0.2mM PL and more whole cells was performed, it resulted in an 80% conversion yield. Furthermore, when barium-alginate immobilization was applied, it showed a 90% conversion yield in 1h with PL, suggesting that it is compatible with developed whole-cell systems without a direct supply of exogenous PLP.
Assuntos
Cadaverina/biossíntese , Escherichia coli/metabolismo , Piridoxal Quinase/metabolismo , Fosfato de Piridoxal/metabolismo , Biotecnologia , Biotransformação , Carboxiliases/metabolismo , Células Imobilizadas , Escherichia coli/genética , Proteínas de Escherichia coli/metabolismo , Lisina/metabolismo , Piridoxal/metabolismoRESUMO
Our study aims to explore the effects of lentivirus-mediated microRNA-124 (miR-124) gene-modified bone marrow mesenchymal stem cell (BMSC) transplantation on the repair of spinal cord injury (SCI) in rats. BMSCs were isolated from the bone marrow of rats. The target gene miR-124 was identified using a luciferase-reporter gene assay. Seventy-two rats were selected for construction of the SCI model, and the rats were randomly divided into the blank group, sham group, SCI group, negative control (NC) group, overexpressed miR-124 group and si-PDXK group. The mRNA expression of miR-124 and the mRNA and protein expression of pyridoxal kinase (PDXK) were detected by quantitative real-time polymerase chain reaction and western blotting. The locomotor capacity of the rats was evaluated using the Basso, Beattie and Bresnahan (BBB) scale. Brdu, neuron-specific enolase (NSE), neurofilament (NF) and microtubule-associated protein 2 (MAP2) were detected using immunohistochemistry. The expression levels of thyrotropin-releasing hormone (TRH), prostacyclin (PGI2) and gangliosides (GM) were measured using an enzyme-linked immunosorbent assay. PDXK was identified as the target gene of miR-124. The overexpressed miR-124 group exhibited higher miR-124 expression than the SCI, NC and si-PDXK groups. Compared with the SCI and NC groups, the PDXK expression was downregulated in the overexpressed miR-124 and si-PDXK groups, and the BBB scores were significantly increased 7, 21 and 35 days after transplantation. The double-labeled positive cell densities (Brdu+NSE/NF/MAP2) and the expression levels of TRH, PGI2 and GM in the overexpressed miR-124 group were significantly higher than those in the NC and SCI groups. These results indicated that miR-124 targeted PDXK to accelerate the differentiation of BMSCs into neurocytes and promote SCI repair.
Assuntos
Transplante de Células-Tronco Mesenquimais/métodos , Células-Tronco Mesenquimais/metabolismo , MicroRNAs/genética , Terapêutica com RNAi , Traumatismos da Medula Espinal/terapia , Regeneração da Medula Espinal , Animais , Células Cultivadas , Epoprostenol/metabolismo , Gangliosídeos/metabolismo , Filamentos Intermediários/genética , Filamentos Intermediários/metabolismo , Lentivirus/genética , MicroRNAs/metabolismo , Proteínas Associadas aos Microtúbulos/genética , Proteínas Associadas aos Microtúbulos/metabolismo , Fosfopiruvato Hidratase/genética , Fosfopiruvato Hidratase/metabolismo , Piridoxal Quinase/genética , Piridoxal Quinase/metabolismo , Ratos , Ratos Sprague-Dawley , Hormônio Liberador de Tireotropina/metabolismoRESUMO
The vitamin B6 salvage pathway, involving pyridoxine 5'-phosphate oxidase (PNPOx) and pyridoxal kinase (PLK), recycles B6 vitamers from nutrients and protein turnover to produce pyridoxal 5'-phosphate (PLP), the catalytically active form of the vitamin. Regulation of this pathway, widespread in living organisms including humans and many bacteria, is very important to vitamin B6 homeostasis but poorly understood. Although some information is available on the enzymatic regulation of PNPOx and PLK, little is known on their regulation at the transcriptional level. In the present work, we identified a new MocR-like regulator, PtsJ from Salmonella typhimurium, which controls the expression of the pdxK gene encoding one of the two PLKs expressed in this organism (PLK1). Analysis of pdxK expression in a ptsJ knockout strain demonstrated that PtsJ acts as a transcriptional repressor. This is the first case of a MocR-like regulator acting as repressor of its target gene. Expression and purification of PtsJ allowed a detailed characterisation of its effector and DNA-binding properties. PLP is the only B6 vitamer acting as effector molecule for PtsJ. A DNA-binding region composed of four repeated nucleotide sequences is responsible for binding of PtsJ to its target promoter. Analysis of binding stoichiometry revealed that protein subunits/DNA molar ratio varies from 4 : 1 to 2 : 1, depending on the presence or absence of PLP. Structural characteristics of DNA transcriptional factor-binding sites suggest that PtsJ binds DNA according to a different model with respect to other characterised members of the MocR subgroup.
Assuntos
Proteínas de Bactérias/química , Regulação Bacteriana da Expressão Gênica , Piridoxal Quinase/química , Piridoxaminafosfato Oxidase/química , Proteínas Repressoras/química , Salmonella typhimurium/metabolismo , Vitamina B 6/química , Sequência de Aminoácidos , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Sítios de Ligação , Clonagem Molecular , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Bacteriano/metabolismo , Escherichia coli/genética , Escherichia coli/metabolismo , Expressão Gênica , Modelos Moleculares , Ligação Proteica , Domínios e Motivos de Interação entre Proteínas , Estrutura Secundária de Proteína , Piridoxal Quinase/genética , Piridoxal Quinase/metabolismo , Fosfato de Piridoxal/química , Fosfato de Piridoxal/metabolismo , Piridoxaminafosfato Oxidase/genética , Piridoxaminafosfato Oxidase/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Salmonella typhimurium/química , Alinhamento de Sequência , Homologia Estrutural de Proteína , Transcrição Gênica , Vitamina B 6/metabolismoRESUMO
AIMS/HYPOTHESIS: We aimed to investigate the potential mechanisms involved in the compromised adipogenesis of visceral (VAT) vs subcutaneous adipose tissue (SAT) using comparative metabolomics. Based on the differentially identified metabolites, we focused on the relationship between the active form of vitamin B6 (pyridoxal 5-phosphate [PLP]), known to be generated through pyridoxal kinase (PDXK), and adipogenesis. METHODS: Non-targeted metabolomics analyses were performed in paired VAT and SAT (n = 14, discovery cohort). PDXK gene expression was evaluated in two validation cohorts of paired SAT and VAT samples in relation to obesity status and insulin sensitivity, and mechanistically after weight loss in vivo and in 3T3-L1 cells in vitro. RESULTS: Comparative metabolomics showed that PLP was significantly decreased in VAT vs SAT. Concordantly, PDXK mRNA levels were significantly decreased in VAT vs SAT, specifically in adipocytes. The decrease was specially marked in obese individuals. PDXK mRNA levels showed a strong association with adipogenic, lipid-droplet-related and lipogenic genes. At a functional level, systemic insulin sensitivity positively associated with PDXK expression, and surgically-induced weight loss (improving insulin sensitivity) led to increased SAT PDXK mRNA levels in parallel with adipogenic genes. In human pre-adipocytes, PDXK mRNA levels increased during adipocyte differentiation and after administration of peroxisome proliferator-activated receptor-γ agonists, and decreased under inflammatory stimuli. Mechanistic studies in 3T3-L1 cells showed that PLP administration resulted in increased adipogenic mRNA markers during early adipogenesis, whereas the PLP antagonist 4-deoxypyridoxine exerted opposite effects. CONCLUSIONS/INTERPRETATION: Overall, these results support the notion that in situ production of PLP is required for physiological adipogenesis.