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Grzechowiak M, Sliwiak J, Link A, Ruszkowski M. Legume-type glutamate dehydrogenase: Structure, activity, and inhibition studies. Int J Biol Macromol 2024; 278:134648. [PMID: 39142482 DOI: 10.1016/j.ijbiomac.2024.134648] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Revised: 06/28/2024] [Accepted: 08/08/2024] [Indexed: 08/16/2024]
Abstract
Glutamate dehydrogenases (GDHs) are key enzymes at the crossroads of N and C metabolism in plants. Legumes, whose N metabolism is particularly intricate, possess a unique type of GDH. This study presents an analysis of a legume-type GDH (isoform 2) from Medicago truncatula (MtGDH2). We measured MtGDH2 activity in both the Glu → 2-oxoglutarate (2OG) and 2OG → Glu reaction directions and obtained kinetic parameters for Glu, 2OG, NAD+, and NADH. Inhibition assays revealed that compounds possessing di- or tricarboxylates act as inhibitors of plant GDHs. Interestingly, 2,6-pyridinedicarboxylate (PYR) weakly inhibits MtGDH2 compared to Arabidopsis thaliana homologs. Furthermore, we explored tetrazole derivatives to discover 3-(1H-tetrazol-5-yl)benzoic acid (TBA) as an MtGDH2 inhibitor. The kinetic experiments are supported by six crystal structures, solved as: (i) unliganded enzyme, (ii) trapping the reaction intermediate 2-amino-2-hydroxyglutarate and NAD+, and also complexed with NAD+ and inhibitors such as (iii) citrate, (iv) PYR, (v) isophthalate, and (vi) TBA. The complex with TBA revealed a new mode of action that, in contrast to other inhibitors, prevents domain closure. This discovery points to TBA as a starting point for the development of novel GDH inhibitors to study the functions of GDH in plants and potentially boost biomass production.
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Affiliation(s)
- Marta Grzechowiak
- Department of Structural Biology of Eukaryotes, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan 61-704, Poland
| | - Joanna Sliwiak
- Laboratory of Protein Engineering, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan 61-704, Poland
| | - Andreas Link
- Department of Pharmaceutical and Medicinal Chemistry, Institute of Pharmacy, University of Greifswald, 17489 Greifswald, Germany
| | - Milosz Ruszkowski
- Department of Structural Biology of Eukaryotes, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan 61-704, Poland.
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2
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Ozone reduces the fruit decay of postharvest winter jujube by altering the microbial community structure on fruit surface. Microbiol Res 2022; 262:127110. [DOI: 10.1016/j.micres.2022.127110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Revised: 04/19/2022] [Accepted: 06/28/2022] [Indexed: 11/20/2022]
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Godsora BKJ, Prakash P, Punekar NS, Bhaumik P. Molecular insights into the inhibition of glutamate dehydrogenase by the dicarboxylic acid metabolites. Proteins 2021; 90:810-823. [PMID: 34748226 DOI: 10.1002/prot.26276] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 11/02/2021] [Accepted: 11/03/2021] [Indexed: 12/20/2022]
Abstract
Glutamate dehydrogenase (GDH) is a salient metabolic enzyme which catalyzes the NAD+ - or NADP+ -dependent reversible conversion of α-ketoglutarate (AKG) to l-glutamate; and thereby connects the carbon and nitrogen metabolism cycles in all living organisms. The function of GDH is extensively regulated by both metabolites (citrate, succinate, etc.) and non-metabolites (ATP, NADH, etc.) but sufficient molecular evidences are lacking to rationalize the inhibitory effects by the metabolites. We have expressed and purified NADP+ -dependent Aspergillus terreus GDH (AtGDH) in recombinant form. Succinate, malonate, maleate, fumarate, and tartrate independently inhibit the activity of AtGDH to different extents. The crystal structures of AtGDH complexed with the dicarboxylic acid metabolites and the coenzyme NADPH have been determined. Although AtGDH structures are not complexed with substrate; surprisingly, they acquire super closed conformation like previously reported for substrate and coenzyme bound catalytically competent Aspergillus niger GDH (AnGDH). These dicarboxylic acid metabolites partially occupy the same binding pocket as substrate; but interact with varying polar interactions and the coenzyme NADPH binds to the Domain-II of AtGDH. The low inhibition potential of tartrate as compared to other dicarboxylic acid metabolites is due to its weaker interactions of carboxylate groups with AtGDH. Our results suggest that the length of carbon skeleton and positioning of the carboxylate groups of inhibitors between two conserved lysine residues at the GDH active site might be the determinants of their inhibitory potency. Molecular details on the dicarboxylic acid metabolites bound AtGDH active site architecture presented here would be applicable to GDHs in general.
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Affiliation(s)
| | - Prem Prakash
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Narayan S Punekar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Prasenjit Bhaumik
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
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4
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Development of a colorimetric α-ketoglutarate detection assay for prolyl hydroxylase domain (PHD) proteins. J Biol Chem 2021; 296:100397. [PMID: 33571527 PMCID: PMC7961094 DOI: 10.1016/j.jbc.2021.100397] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 02/01/2021] [Accepted: 02/04/2021] [Indexed: 11/20/2022] Open
Abstract
Since the discovery of the prolyl hydroxylases domain (PHD) proteins and their canonical hypoxia-inducible factor (HIF) substrate two decades ago, a number of in vitro hydroxylation (IVH) assays for PHD activity have been developed to measure the PHD-HIF interaction. However, most of these assays either require complex proteomics mass spectrometry methods that rely on the specific PHD-HIF interaction or require the handling of radioactive material, as seen in the most commonly used assay measuring [14C]O2 release from labeled [14C]α-ketoglutarate. Here, we report an alternative rapid, cost-effective assay in which the consumption of α-ketoglutarate is monitored by its derivatization with 2,4-dinitrophenylhydrazine (2,4-DNPH) followed by treatment with concentrated base. We extensively optimized this 2,4-DNPH α-ketoglutarate assay to maximize the signal-to-noise ratio and demonstrated that it is robust enough to obtain kinetic parameters of the well-characterized PHD2 isoform comparable with those in published literature. We further showed that it is also sensitive enough to detect and measure the IC50 values of pan-PHD inhibitors and several PHD2 inhibitors in clinical trials for chronic kidney disease (CKD)-induced anemia. Given the efficiency of this assay coupled with its multiwell format, the 2,4-DNPH α-KG assay may be adaptable to explore non-HIF substrates of PHDs and potentially to high-throughput assays.
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Pathan EK, Kulkarni AM, Prasanna NVL, Ramana CV, Deshpande MV. NADP-dependent glutamate dehydrogenases in a dimorphic zygomycete Benjaminiella poitrasii: Purification, characterization and their evaluation as an antifungal drug target. Biochim Biophys Acta Gen Subj 2020; 1864:129696. [PMID: 32768460 DOI: 10.1016/j.bbagen.2020.129696] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 07/14/2020] [Accepted: 07/22/2020] [Indexed: 10/23/2022]
Abstract
BACKGROUND It has been reported that the genes coding for NADP-dependent glutamate dehydrogenases (NADP-GDHs) showed a cause-effect relationship with Yeast-Hypha (YH) reversible transition in a zygomycete Benjaminiella poitrasii. As YH transition is significant in human pathogenic fungi for their survival and proliferation in the host, the NADP-GDHs can be explored as antifungal drug targets. METHODS The yeast-form specific BpNADPGDH I and hyphal-form specific BpNADPGDH II of B. poitrasii were purified by heterologous expression in E. coli BL-21 cells and characterized. The structural analogs of L-glutamate, dimethyl esters of isophthalic acid (DMIP) and its derivatives were designed, synthesized and screened for inhibition of NADP-GDH activity as well as YH transition in B. poitrasii, and also in human pathogenic Candida albicans strains. RESULTS The BpNADPGDH I and BpNADPGDH II were found to be homo-hexameric proteins with native molecular mass of 282 kDa and 298 kDa, respectively and subunit molecular weights of 47 kDa and 49 kDa, respectively. Besides the distinct kinetic properties, BpNADPGDH I and BpNADPGDH II were found to be regulated by cAMP-dependent- and Calmodulin (CaM) dependent- protein kinases, respectively. The DMIP compounds showed a more pronounced effect on H-form specific BpNADPGDH II and inhibited YH transition as well as growth in B. poitrasii and C. albicans strains. CONCLUSION The present study will be useful to design and develop antifungal drugs against dimorphic human pathogens using glutamate dehydrogenase as a target. SIGNIFICANCE Glutamate dehydrogenases can be explored as a target against human pathogenic fungi.
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Affiliation(s)
- Ejaj K Pathan
- Biochemical Sciences Division, CSIR-National Chemical Laboratory, Pune 411008, India.
| | - Anand M Kulkarni
- Division of organic chemistry, CSIR-National Chemical Laboratory, Pune 411008, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | | | - Chepuri V Ramana
- Division of organic chemistry, CSIR-National Chemical Laboratory, Pune 411008, India
| | - Mukund V Deshpande
- Biochemical Sciences Division, CSIR-National Chemical Laboratory, Pune 411008, India.
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Agarwal N, Walvekar AS, Punekar NS. 2-Oxoglutarate cooperativity and biphasic ammonium saturation of Aspergillus niger NADP-glutamate dehydrogenase are structurally coupled. Arch Biochem Biophys 2019; 669:50-60. [PMID: 31136734 DOI: 10.1016/j.abb.2019.05.018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Revised: 05/22/2019] [Accepted: 05/24/2019] [Indexed: 11/18/2022]
Abstract
NADP-glutamate dehydrogenase from Aspergillus niger (AnGDH) exhibits sigmoidal 2-oxoglutarate saturation. Despite sharing 88% amino acid identity, the homologous enzyme from Aspergillus terreus (AtGDH) shows hyperbolic 2-oxoglutarate saturation. In order to address the structural origins of this phenomenon, six AnGDH-AtGDH chimeras were constructed and characterized. The C-terminal sequence (residues 315-460, named the D-segment) was implicated in the AnGDH cooperativity. The D-segment residues largely contribute to the monomer-monomer interface of each trimer in the native hexamer and are far removed from the enzyme active site. The D-segment appears to be a part of the allosteric network responsible for 2-oxoglutarate homotropic interactions in AnGDH. AnGDH and its C415S mutant, but not AtGDH, also showed atypical, biphasic ammonium saturation, particularly at sub-saturating 2-oxoglutarate concentrations. We found that the sigmoidal 2-oxoglutarate saturation and the biphasic ammonium response are tightly coupled; the analysis of AnGDH-AtGDH chimeras ascribes the two features to the AnGDH D-segment. The two non-Michaelis-Menten substrate saturations of AnGDH were influenced by ionic strength. Increase in ionic strength reduced the nH of 2-oxoglutarate saturation as well as abolished the biphasic response, suggesting that polar/ionic interactions determine the allosteric, inter-subunit communications. The biochemical analysis in the context of available structural data implicates the D-segment of AnGDH in the allosteric feature of this enzyme. The coupling of sigmoidal 2-oxoglutarate saturation and the biphasic ammonium response could possibly confer growth advantage to A. niger experiencing carbon and/or nitrogen limitation.
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Affiliation(s)
- Nupur Agarwal
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, 400076, Maharashtra, India
| | - Adhish S Walvekar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, 400076, Maharashtra, India
| | - Narayan S Punekar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, 400076, Maharashtra, India.
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Prakash P, Punekar NS, Bhaumik P. Structural basis for the catalytic mechanism and α-ketoglutarate cooperativity of glutamate dehydrogenase. J Biol Chem 2018. [PMID: 29540480 DOI: 10.1074/jbc.ra117.000149] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glutamate dehydrogenase (GDH) is a key enzyme connecting carbon and nitrogen metabolism in all living organisms. Despite extensive studies on GDHs from both prokaryotic and eukaryotic organisms in the last 40 years, the structural basis of the catalytic features of this enzyme remains incomplete. This study reports the structural basis of the GDH catalytic mechanism and allosteric behavior. We determined the first high-resolution crystal structures of glutamate dehydrogenase from the fungus Aspergillus niger (AnGDH), a unique NADP+-dependent allosteric enzyme that is forward-inhibited by the formation of mixed disulfide. We determined the structures of the active enzyme in its apo form and in binary/ternary complexes with bound substrate (α-ketoglutarate), inhibitor (isophthalate), coenzyme (NADPH), or two reaction intermediates (α-iminoglutarate and 2-amino-2-hydroxyglutarate). The structure of the forward-inhibited enzyme (fiAnGDH) was also determined. The hexameric AnGDH had three open subunits at one side and three partially closed protomers at the other, a configuration not previously reported. The AnGDH hexamers having subunits with different conformations indicated that its α-ketoglutarate-dependent homotropic cooperativity follows the Monod-Wyman-Changeux (MWC) model. Moreover, the position of the water attached to Asp-154 and Gly-153 defined the previously unresolved ammonium ion-binding pocket, and the binding site for the 2'-phosphate group of the coenzyme was also better defined by our structural data. Additional structural and mutagenesis experiments identified the residues essential for coenzyme recognition. This study reveals the structural features responsible for positioning α-ketoglutarate, NADPH, ammonium ion, and the reaction intermediates in the GDH active site.
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Affiliation(s)
- Prem Prakash
- From the Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India
| | - Narayan S Punekar
- From the Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India
| | - Prasenjit Bhaumik
- From the Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India
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Zhu J, Lu K, Xu X, Wang X, Shi J. Purification and characterization of a novel glutamate dehydrogenase from Geotrichum candidum with higher alcohol and amino acid activity. AMB Express 2017; 7:9. [PMID: 28050850 PMCID: PMC5209314 DOI: 10.1186/s13568-016-0307-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Accepted: 12/14/2016] [Indexed: 11/10/2022] Open
Abstract
Crude enzyme from Geotrichum candidum S12 exhibited high activity towards hexanol at pH 4.0, distinguishing it from currently known enzymes. To identify the dominant enzyme contributing to this activity, the crude enzyme extract was separated into different fractions by ammonium sulfate precipitation, MonoQ anion-exchange chromatography, and Sephacryl S-200 gel filtration chromatography. Afraction with high activity towards hexanol at pH 4.0 was obtained, exhibiting 38-fold improved purity and a specific activity of 3802.7 U/mg. After electrophoretic analysis, the fraction showed a molecular weight of 223 kDa by Native-PAGE and 51.4 kDa by SDS-PAGE. The purified fraction was identified as a glutamate dehydrogenase (GDH) by peptide mass fingerprinting data. This fraction showed high activity towards glutamate, α-ketoglutarate, hexanol, and isoamyl alcohol with a Km value of 41.74, 4.01, 20.37, and 19.37 mM, respectively, but with no activity towards methanol, ethanol, 1-propanol, and isobutanol. As a comparison, the GDH from yeast had no activity towards hexanol and other alcohols. Kinetic analysis revealed that glutamate and hexanol served as competitive inhibitors to each other for the purified GDH. The GDH showed the highest activity towards hexanol at pH 4.0 and 30 °C, and was the most stable at pH 2.2-7.0 and ≤40 °C. The presence of ADP, Fe2+, K+, and Zn2+ increased the enzymatic activity towards hexanol and EDTA, Pb2+, Mn2+, ATP, and DTT decreased the activity. These novel characteristics expand the reported properties of GDH and suggest the newly characterized GDH has unique potential for practical application.
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9
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Inhibitors of amino acids biosynthesis as antifungal agents. Amino Acids 2014; 47:227-49. [PMID: 25408465 PMCID: PMC4302243 DOI: 10.1007/s00726-014-1873-1] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Accepted: 11/05/2014] [Indexed: 12/22/2022]
Abstract
Fungal microorganisms, including the human pathogenic yeast and filamentous fungi, are able to synthesize all proteinogenic amino acids, including nine that are essential for humans. A number of enzymes catalyzing particular steps of human-essential amino acid biosynthesis are fungi specific. Numerous studies have shown that auxotrophic mutants of human pathogenic fungi impaired in biosynthesis of particular amino acids exhibit growth defect or at least reduced virulence under in vivo conditions. Several chemical compounds inhibiting activity of one of these enzymes exhibit good antifungal in vitro activity in minimal growth media, which is not always confirmed under in vivo conditions. This article provides a comprehensive overview of the present knowledge on pathways of amino acids biosynthesis in fungi, with a special emphasis put on enzymes catalyzing particular steps of these pathways as potential targets for antifungal chemotherapy.
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Prakash P, Walvekar AS, Punekar NS, Bhaumik P. Purification, crystallization and preliminary X-ray diffraction analysis of NADP-dependent glutamate dehydrogenase from Aspergillus niger. Acta Crystallogr F Struct Biol Commun 2014; 70:1508-12. [PMID: 25372818 PMCID: PMC4231853 DOI: 10.1107/s2053230x14021499] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Accepted: 09/29/2014] [Indexed: 11/10/2022] Open
Abstract
Glutamate dehydrogenase (GDH) catalyzes the NAD-dependent or NADP-dependent oxidative deamination of L-glutamate to 2-oxoglutarate and ammonia. This important reversible reaction establishes the link between carbon and nitrogen metabolism. In this study, Aspergillus niger NADP-GDH (AnGDH) has been overexpressed and purified. Purified AnGDH, with a high specific activity of 631.1 units per milligram of protein, was crystallized and the crystal diffracted to 2.9 Å resolution using a home X-ray source. Preliminary analysis of the X-ray diffraction data showed that the crystal belonged to space group R32, with unit-cell parameters a=b=173.8, c=241.5 Å, α=β=90, γ=120°. The crystals exhibited an unusually high solvent content (83.0%) and had only one molecule in the asymmetric unit. Initial phases were obtained by molecular replacement, and model building and structure refinement of AnGDH are in progress.
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Affiliation(s)
- Prem Prakash
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
| | - Adhish S. Walvekar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
| | - Narayan S. Punekar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
| | - Prasenjit Bhaumik
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
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Joshi CV, Pathan EK, Punekar NS, Tupe SG, Kapadnis BP, Deshpande MV. A biochemical correlate of dimorphism in a zygomycete Benjaminiella poitrasii: characterization of purified NAD-dependent glutamate dehydrogenase, a target for antifungal agents. Antonie van Leeuwenhoek 2013; 104:25-36. [PMID: 23588417 DOI: 10.1007/s10482-013-9921-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Accepted: 04/05/2013] [Indexed: 10/27/2022]
Abstract
The fungal organisms, especially pathogens, change their vegetative (Y, unicellular yeast and H, hypha) morphology reversibly for survival and proliferation in the host environment. NAD-dependent glutamate dehydrogenase (NAD-GDH, EC 1.4.1.2) from a non-pathogenic dimorphic zygomycete Benjaminiella poitrasii was previously reported to be an important biochemical correlate of the transition process. The enzyme was purified to homogeneity and characterized. It is a 371 kDa native molecular weight protein made up of four identical subunits. Kinetic studies showed that unlike other NAD-GDHs, it may act as an anabolic enzyme and has more affinity towards 2-oxoglutarate than L-glutamate. Chemical modifications revealed the involvement of single histidine and lysine residues in the catalytic activity of the enzyme. The phosphorylation and dephosphorylation study showed that the NAD-GDH is present in active phosphorylated form in hyphal cells of B. poitrasii. Two of the 1,2,3 triazole linked β-lactam-bile acid conjugates synthesized in the laboratory (B18, B20) were found to be potent inhibitors of purified NAD-GDH which also significantly affected Y-H transition in B. poitrasii. Furthermore, the compound B20 inhibited germ tube formation during Y-H transition in Candida albicans strains and Yarrowia lipolytica. The possible use of NAD-GDH as a target for antifungal agents is discussed.
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Affiliation(s)
- C V Joshi
- Biochemical Sciences Division, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
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Effect of Ferrous Ion on ε-Poly-l-Lysine Biosynthesis by Streptomyces diastatochromogenes CGMCC3145. Curr Microbiol 2010; 62:1062-7. [DOI: 10.1007/s00284-010-9828-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Accepted: 11/18/2010] [Indexed: 12/31/2022]
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Bypassing isophthalate inhibition by modulating glutamate dehydrogenase (GDH): purification and kinetic characterization of NADP-GDHs from isophthalate-degrading Pseudomonas aeruginosa strain PP4 and Acinetobacter lwoffii strain ISP4. J Bacteriol 2009; 192:801-6. [PMID: 19933355 DOI: 10.1128/jb.01365-09] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pseudomonas aeruginosa strain PP4 and Acinetobacter lwoffii strain ISP4 metabolize isophthalate as a sole source of carbon and energy. Isophthalate is known to be a competitive inhibitor of glutamate dehydrogenase (GDH), which is involved in C and N metabolism. Strain PP4 showed carbon source-dependent modulation of NADP-GDH; GDH(I) was produced when cells were grown on isophthalate, while GDH(II) was produced when cells were grown on glucose. Strain ISP4 produced a single form of NADP-GDH, GDH(P), when it was grown on either isophthalate or rich medium (2YT). All of the forms of GDH were purified to homogeneity and characterized. GDH(I) and GDH(II) were found to be homotetramers, while GDH(P) was found to be a homohexamer. GDH(II) was more sensitive to inhibition by isophthalate (2.5- and 5.5-fold more sensitive for amination and deamination reactions, respectively) than GDH(I). Differences in the N-terminal sequences and electrophoretic mobilities in an activity-staining gel confirmed the presence of two forms of GDH, GDH(I) and GDH(II), in strain PP4. In strain ISP4, irrespective of the carbon source, the GDH(P) produced showed similar levels of inhibition with isophthalate. However, the specific activity of GDH(P) from isophthalate-grown cells was 2.5- to 3-fold higher than that of GDH(P) from 2YT-grown cells. Identical N-terminal sequences and electrophoretic mobilities in the activity-staining gel suggested the presence of a single form of GDH(P) in strain ISP4. These results demonstrate the ability of organisms to modulate GDH either by producing an entirely different form or by increasing the level of the enzyme, thus enabling strains to utilize isophthalate more efficiently as a sole source of carbon and energy.
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Aspergillus terreus NADP-glutamate dehydrogenase is kinetically distinct from the allosteric enzyme of other Aspergilli. ACTA ACUST UNITED AC 2009; 113:1121-6. [DOI: 10.1016/j.mycres.2009.07.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Accepted: 07/14/2009] [Indexed: 11/18/2022]
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Rangel OA, Gómez-Baena G, López-Lozano A, Diez J, García-Fernández JM. Physiological role and regulation of glutamate dehydrogenase in Prochlorococcus sp. strain MIT9313. ENVIRONMENTAL MICROBIOLOGY REPORTS 2009; 1:56-64. [PMID: 23765721 DOI: 10.1111/j.1758-2229.2008.00005.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Glutamate dehydrogenase is an enzyme catalysing a reaction for ammonium assimilation, alternative to those performed by glutamine synthetase and glutamate synthase. In the genus Prochlorococcus, genomic studies have shown the presence of the gdhA gene (encoding glutamate dehydrogenase) in only four of the sequenced strains, including MIT9313. We studied the physiological regulation of glutamate dehydrogenase in this strain, by measuring the expression of gdhA, the intracellular concentration of the enzyme and its activity. Our goal was to clarify the physiological role of glutamate dehydrogenase, in order to understand why it has been selectively conserved in certain strains. Studies performed in cultures under nitrogen starvation, or with inhibitors of the nitrogen assimilation, suggest that the main role of glutamate dehydrogenase is not the assimilation of ammonium. Glutamate dehydrogenase activity and gdhA expression increased along the growth of cultures. Besides, we found a significant upregulation in gene expression when cultures were grown on glutamate as nitrogen source. We suggest that the main physiological role of glutamate dehydrogenase in Prochlorococcus MIT9313 is the utilization of glutamate to produce ammonium and 2-oxoglutarate, and amino acid recycling, thus enabling to use amino acids as nitrogen source. Therefore we propose that glutamate dehydrogenase is present in the genome of strains for whom the utilization of amino acids is most important.
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Affiliation(s)
- Oriol Alberto Rangel
- Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, 14071-Córdoba, Spain
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Choudhury R, Noor S, Varadarajalu LP, Punekar NS. Delineation of an in vivo inhibitor for Aspergillus glutamate dehydrogenase. Enzyme Microb Technol 2007; 42:151-9. [PMID: 22578865 DOI: 10.1016/j.enzmictec.2007.08.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2007] [Revised: 08/29/2007] [Accepted: 08/30/2007] [Indexed: 11/18/2022]
Abstract
NADP-glutamate dehydrogenase (NADP-GDH) along with glutamine synthetase plays a pivotal role in ammonium assimilation. Specific inhibitors were valuable in defining the importance of glutamine synthetase in nitrogen metabolism. Selective in vivo inhibition of NADP-GDH has so far been an elusive desideratum. Isophthalate, a potent in vitro inhibitor of Aspergillus niger NADP-GDH [Noor S, Punekar NS. Allosteric NADP-glutamate dehydrogenase from aspergilli: purification, characterization and implications for metabolic regulation at the carbon-nitrogen interface. Microbiology 2005;151:1409-19], was evaluated for its efficacy in vivo. Dimethyl ester of isophthalate (DMIP), but not isophthalate, inhibited A. niger growth on agar as well as in liquid culture. This was ascribed to the inability of isophthalate to enter fungal mycelia. Subsequent to DMIP addition however, intracellular isophthalate could be demonstrated. Apart from NAD-GDH, no other enzyme including NAD-glutamate synthase was inhibited by isophthalate. A cross-over at NADP-GDH step of metabolism was observed as a direct consequence of isophthalate (formed in vivo from DMIP) inhibiting this enzyme. Addition of ammonium to DMIP-treated A. niger mycelia resulted in intensive vacuolation, retraction of cytoplasm and autolysis. Taken together, these results implicate glutamate dehydrogenase and NADP-GDH in particular, as a key target of in vivo isophthalate inhibition during ammonium assimilation.
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Affiliation(s)
- Rajarshi Choudhury
- Biotechnology Group, School of Bioscience and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, Maharashtra, India
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