Structural and kinetic differences between human and Aspergillus fumigatusD-glucosamine-6-phosphate N-acetyltransferase

2008 ◽  
Vol 415 (2) ◽  
pp. 217-223 ◽  
Author(s):  
Ramon Hurtado-Guerrero ◽  
Olawale G. Raimi ◽  
Jinrong Min ◽  
Hong Zeng ◽  
Laura Vallius ◽  
...  
Keyword(s):  
Active Site ◽  
Gene Disruption ◽  
Biosynthetic Pathway ◽  
Binding Pocket ◽  
Immunocompromised Patients ◽  
Kinetic Characterization ◽  
Phosphate Binding ◽  
Fungal Enzyme ◽  
Pathway Gene ◽  
Steady State Kinetics

Aspergillus fumigatus is the causative agent of aspergillosis, a frequently invasive colonization of the lungs of immunocompromised patients. GNA1 (D-glucosamine-6-phosphate N-acetyltransferase) catalyses the acetylation of GlcN-6P (glucosamine-6-phosphate) to GlcNAc-6P (N-acetylglucosamine-6-phosphate), a key intermediate in the UDP-GlcNAc biosynthetic pathway. Gene disruption of gna1 in yeast and Candida albicans has provided genetic validation of the enzyme as a potential target. An understanding of potential active site differences between the human and A. fumigatus enzymes is required to enable further work aimed at identifying selective inhibitors for the fungal enzyme. In the present study, we describe crystal structures of both human and A. fumigatus GNA1, as well as their kinetic characterization. The structures show significant differences in the sugar-binding site with, in particular, several non-conservative substitutions near the phosphate-binding pocket. Mutagenesis targeting these differences revealed drastic effects on steady-state kinetics, suggesting that the differences could be exploitable with small-molecule inhibitors.

3′-Azidothymidine in the active site ofEscherichia colithymidine phosphorylase: the peculiarity of the binding on the basis of X-ray study

2014 ◽  
Vol 70 (4) ◽  
pp. 1155-1165 ◽  
Author(s):  
Vladimir Timofeev ◽  
Yulia Abramchik ◽  
Nadezda Zhukhlistova ◽  
Tatiana Muravieva ◽  
Ilya Fateev ◽  
...  
Keyword(s):  
Active Site ◽  
Thymidine Phosphorylase ◽  
Binding Pocket ◽  
Chemotherapeutic Agents ◽  
Nucleoside Analogues ◽  
Dimensional Structure ◽  
Phosphate Binding ◽  
X Ray ◽  
E Coli ◽  
Replacement Method

The structural study of complexes of thymidine phosphorylase (TP) with nucleoside analogues which inhibit its activity is of special interest because many of these compounds are used as chemotherapeutic agents. Determination of kinetic parameters showed that 3′-azido-3′-deoxythymidine (3′-azidothymidine; AZT), which is widely used for the treatment of human immunodeficiency virus, is a reversible noncompetitive inhibitor ofEscherichia colithymidine phosphorylase (TP). The three-dimensional structure ofE. coliTP complexed with AZT was solved by the molecular-replacement method and was refined at 1.52 Å resolution. Crystals for X-ray study were grown in microgravity by the counter-diffusion technique from a solution of the protein in phosphate buffer with ammonium sulfate as a precipitant. The AZT molecule was located with full occupancy in the electron-density maps in the nucleoside-binding pocket of TP, whereas the phosphate-binding pocket of the enzyme was occupied by phosphate (or sulfate) ion. The structure of the active-site cavity and conformational changes of the enzyme upon AZT binding are described in detail. It is found that the position of AZT differs remarkably from the positions of the pyrimidine bases and nucleoside analogues in other known complexes of pyrimidine phosphorylases, but coincides well with the position of 2′-fluoro-3′-azido-2′,3′-dideoxyuridine (N3FddU) in the recently investigated complex ofE. coliTP with this ligand (Timofeevet al., 2013). The peculiarities of the arrangement of N3FddU and 3′-azidothymidine in the nucleoside binding pocket of TP and correlations between the arrangement and inhibitory properties of these compounds are discussed.

scholarly journals Structural basis for DNA 5´-end resection by RecJ

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Kaiying Cheng ◽  
Hong Xu ◽  
Xuanyi Chen ◽  
Liangyan Wang ◽  
Bing Tian ◽  
...  
Keyword(s):  
Active Site ◽  
Deinococcus Radiodurans ◽  
Divalent Cations ◽  
Binding Pocket ◽  
Structural Basis ◽  
Phosphate Binding ◽  
Terminal Domain ◽  
Dna Strand ◽  
Recombination Pathway ◽  
End Resection

The resection of DNA strand with a 5´ end at double-strand breaks is an essential step in recombinational DNA repair. RecJ, a member of DHH family proteins, is the only 5´ nuclease involved in the RecF recombination pathway. Here, we report the crystal structures of Deinococcus radiodurans RecJ in complex with deoxythymidine monophosphate (dTMP), ssDNA, the C-terminal region of single-stranded DNA-binding protein (SSB-Ct) and a mechanistic insight into the RecF pathway. A terminal 5´-phosphate-binding pocket above the active site determines the 5´-3´ polarity of the deoxy-exonuclease of RecJ; a helical gateway at the entrance to the active site admits ssDNA only; and the continuous stacking interactions between protein and nine nucleotides ensure the processive end resection. The active site of RecJ in the N-terminal domain contains two divalent cations that coordinate the nucleophilic water. The ssDNA makes a 180° turn at the scissile phosphate. The C-terminal domain of RecJ binds the SSB-Ct, which explains how RecJ and SSB work together to efficiently process broken DNA ends for homologous recombination.

scholarly journals The Role of Active-Site Plasticity in Damaged-Nucleotide Recognition by Human Apurinic/Apyrimidinic Endonuclease APE1

Molecules ◽  
2020 ◽  
Vol 25 (17) ◽  
pp. 3940
Author(s):  
Anatoly A. Bulygin ◽  
Alexandra A. Kuznetsova ◽  
Yuri N. Vorobjev ◽  
Olga S. Fedorova ◽  
Nikita A. Kuznetsov
Keyword(s):  
Conformational Changes ◽  
Active Site ◽  
Binding Pocket ◽  
Amino Acid Residues ◽  
Abasic Site ◽  
Dna Lesion ◽  
Steady State Kinetics ◽  
Α Helix ◽  
Dynamics Simulations ◽  
Ap Site

Human apurinic/apyrimidinic (AP) endonuclease APE1 hydrolyzes phosphodiester bonds on the 5′ side of an AP-site, and some damaged nucleotides such as 1,N6-ethenoadenosine (εA), α-adenosine (αA), and 5,6-dihydrouridine (DHU). To investigate the mechanism behind the broad substrate specificity of APE1, we analyzed pre-steady-state kinetics of conformational changes in DNA and the enzyme during DNA binding and damage recognition. Molecular dynamics simulations of APE1 complexes with one of damaged DNA duplexes containing εA, αA, DHU, or an F-site (a stable analog of an AP-site) revealed the involvement of residues Asn229, Thr233, and Glu236 in the mechanism of DNA lesion recognition. The results suggested that processing of an AP-site proceeds faster in comparison with nucleotide incision repair substrates because eversion of a small abasic site and its insertion into the active site do not include any unfavorable interactions, whereas the insertion of any target nucleotide containing a damaged base into the APE1 active site is sterically hindered. Destabilization of the α-helix containing Thr233 and Glu236 via a loss of the interaction between these residues increased the plasticity of the damaged-nucleotide binding pocket and the ability to accommodate structurally different damaged nucleotides. Nonetheless, the optimal location of εA or αA in the binding pocket does not correspond to the optimal conformation of catalytic amino acid residues, thereby significantly decreasing the cleavage efficacy for these substrates.

Structural insights into dihydroxylation of terephthalate, a product of polyethylene terephthalate degradation

2022 ◽  
Author(s):  
Jai Krishna Mahto ◽  
Neetu Neetu ◽  
Monica Sharma ◽  
Monika Dubey ◽  
Bhanu Prakash Vellanki ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Substrate Specificity ◽  
Polyethylene Terephthalate ◽  
Active Site ◽  
Catalytic Domain ◽  
Structural Features ◽  
Comamonas Testosteroni ◽  
Plastic Pollution ◽  
Microbial Utilization ◽  
Steady State Kinetics

Biodegradation of terephthalate (TPA) is a highly desired catabolic process for the bacterial utilization of this Polyethylene terephthalate (PET) depolymerization product, but to date, the structure of terephthalate dioxygenase (TPDO), a Rieske oxygenase (RO) that catalyzes the dihydroxylation of TPA to a cis -diol is unavailable. In this study, we characterized the steady-state kinetics and first crystal structure of TPDO from Comamonas testosteroni KF1 (TPDO KF1 ). The TPDO KF1 exhibited the substrate specificity for TPA ( k cat / K m = 57 ± 9 mM −1 s −1 ). The TPDO KF1 structure harbors characteristics RO features as well as a unique catalytic domain that rationalizes the enzyme’s function. The docking and mutagenesis studies reveal that its substrate specificity to TPA is mediated by Arg309 and Arg390 residues, two residues positioned on opposite faces of the active site. Additionally, residue Gln300 is also proven to be crucial for the activity, its substitution to alanine decreases the activity ( k cat ) by 80%. Together, this study delineates the structural features that dictate the substrate recognition and specificity of TPDO. Importance The global plastic pollution has become the most pressing environmental issue. Recent studies on enzymes depolymerizing polyethylene terephthalate plastic into terephthalate (TPA) show some potential in tackling this. Microbial utilization of this released product, TPA is an emerging and promising strategy for waste-to-value creation. Research from the last decade has discovered terephthalate dioxygenase (TPDO), as being responsible for initiating the enzymatic degradation of TPA in a few Gram-negative and Gram-positive bacteria. Here, we have determined the crystal structure of TPDO from Comamonas testosteroni KF1 and revealed that it possesses a unique catalytic domain featuring two basic residues in the active site to recognize TPA. Biochemical and mutagenesis studies demonstrated the crucial residues responsible for the substrate specificity of this enzyme.

Entamoeba histolytica: identification of thioredoxin-targeted proteins and analysis of serine acetyltransferase-1 as a prototype example

2013 ◽  
Vol 451 (2) ◽  
pp. 277-288 ◽  
Author(s):  
Sarah Schlosser ◽  
David Leitsch ◽  
Michael Duchêne
Keyword(s):  
Entamoeba Histolytica ◽  
Active Site ◽  
Gel Electrophoresis ◽  
Biosynthetic Pathway ◽  
Interacting Proteins ◽  
Protozoan Parasites ◽  
Serine Acetyltransferase ◽  
Two Dimensional Gel Electrophoresis ◽  
Mixed Disulfide ◽  
Far Western Blot

Entamoeba histolytica, the causative agent of amoebiasis, possesses the dithiol-containing redox proteins Trx (thioredoxin) and TrxR (Trx reductase). Both proteins were found to be covalently modified and inactivated by metronidazole, a 5-nitroimidazole drug that is commonly used to treat infections with microaerophilic protozoan parasites in humans. Currently, very little is known about enzymes and other proteins participating in the Trx-dependent redox network of the parasite that could be indirectly affected by metronidazole treatment. On the basis of the disulfide/dithiol-exchange mechanism we constructed an active-site mutant of Trx, capable of binding interacting proteins as a stable mixed disulfide intermediate to screen the target proteome of Trx in E. histolytica. By applying Trx affinity chromatography, two-dimensional gel electrophoresis and MS, peroxiredoxin and 15 further potentially redox-regulated proteins were identified. Among them, EhSat1 (E. histolytica serine acetyltransferase-1), an enzyme involved in the L-cysteine biosynthetic pathway, was selected for detailed analysis. Binding of Trx to EhSat1 was verified by Far-Western blot analysis. Trx was able to restore the activity of the oxidatively damaged EhSat1 suggesting that the TrxR/Trx system protects sensitive proteins against oxidative stress in E. histolytica. Furthermore, the activity of peroxiredoxin, which is dependent on a functioning TrxR/Trx system, was strongly reduced in metronidazole-treated parasites.

scholarly journals The fungal gene cluster for biosynthesis of the antibacterial agent viriditoxin

2019 ◽  
Author(s):  
Andrew S. Urquhart ◽  
Jinyu Hu ◽  
Yit-Heng Chooi ◽  
Alexander Idnurm
Keyword(s):  
Secondary Metabolites ◽  
Gene Cluster ◽  
Gene Disruption ◽  
Biosynthetic Pathway ◽  
Fluorescent Protein ◽  
Model Species ◽  
Paecilomyces Variotii ◽  
Bioinformatic Approaches ◽  
Green Fluorescent ◽  
Fungal Gene

AbstractBackgroundViriditoxin is one of the ‘classical’ secondary metabolites produced by fungi and that has antibacterial and other activities; however, the mechanism of its biosynthesis has remained unknown.ResultsHere, a gene cluster responsible for its synthesis was identified, using bioinformatic approaches from two species that produce viriditoxin and then through gene disruption and metabolite profiling. All eight genes in the cluster inPaecilomyces variotiiwere mutated, revealing their roles in the synthesis of this molecule and establishing its biosynthetic pathway which includes an interesting Baeyer-Villiger monooxygenase catalyzed reaction. Additionally, a candidate catalytically-inactive hydrolase was identified as being required for the stereoselective biosynthesis of (M)-viriditoxin. The localization of two proteins were assessed by fusing these proteins to green fluorescent protein, revealing that at least two intracellular structures are involved in the compartmentalization of the synthesis steps of this metabolite.ConclusionsThe full pathway for synthesis of viriditoxin was established by a combination of genomics, bioinformatics, gene disruption and chemical analysis processes. Hence, this work reveals the basis for the synthesis of an understudied class of fungal secondary metabolites and provides a new model species for understanding the synthesis of biaryl compounds with a chiral axis.

scholarly journals Inhibition of Phosphodiesterase 5 Enzyme by Pterine- 6 Carboxylic Acid from Baphia nitida –Related to Erectile Dysfunction: Computational Kinetic

2020 ◽  
pp. 49-55
Author(s):  
Wopara, Iheanyichukwu ◽  
S. K. Mobisson ◽  
Egelege Aziemeola Pius ◽  
A. A. Uwakwe ◽  
M. O. Wegwu
Keyword(s):  
Erectile Dysfunction ◽  
Carboxylic Acid ◽  
Active Site ◽  
In Silico ◽  
Binding Pocket ◽  
Docking Studies ◽  
Drug Candidate ◽  
In Silico Docking ◽  
In Silico Studies ◽  
Phosphodiesterase 5

Treatment of erectile dysfunction is associated with inhibition of Phosphodiesterase 5 enzyme. This study deals with the evaluation of Pterin-6-carboxylic acid inhibitory activity on phosphodiesterase 5 (PDB ID: 4OEW) using in silico docking studies. Pterin-6-carboxylic acid from Baphia nitida was isolated using GC-MS and docked into PDE5 active site. The docking result showed that pterin-6-carboxylic acid bind to the active site of phosphodiesterase 5 with the binding energy value of -7.1 and 2.05A° - 2.23A° when compared with other compound found in the plant. Moreso, docking analysis with the ligand identified specific residues such as: Ile 778, Phe 820, Gln 817, Ser 815 and Gln 775 within the binding pocket which played an important role in the ligand binding affinity to the protein. Result from our In silico studies hypothesized that pterin-6-carboxylic acid can be an inhibitory agent for PDE5 protein which could be a potential drug candidate for the treatment of erectile dysfunction.

scholarly journals Catalytic and structural contributions for glutathione-binding residues in a Delta class glutathione S-transferase

2004 ◽  
Vol 382 (2) ◽  
pp. 751-757 ◽  
Author(s):  
Pakorn WINAYANUWATTIKUN ◽  
Albert J. KETTERMAN
Keyword(s):  
Binding Site ◽  
Active Site ◽  
Structural Integrity ◽  
Catalytic Mechanism ◽  
Tertiary Structure ◽  
Site Directed Mutagenesis ◽  
Active Site Residues ◽  
Anopheles Dirus ◽  
Steady State Kinetics ◽  
Cellular Detoxification

Glutathione S-transferases (GSTs) are dimeric proteins that play a major role in cellular detoxification. The GSTs in mosquito Anopheles dirus species B, an important malaria vector in South East Asia, are of interest because they can play an important role in insecticide resistance. In the present study, we characterized the Anopheles dirus (Ad)GST D3-3 which is an alternatively spliced product of the adgst1AS1 gene. The data from the crystal structure of GST D3-3 shows that Ile-52, Glu-64, Ser-65, Arg-66 and Met-101 interact directly with glutathione. To study the active-site function of these residues, alanine substitution site-directed mutagenesis was performed resulting in five mutants: I52A (Ile-52→Ala), E64A, S65A, R66A and M101A. Interestingly, the E64A mutant was expressed in Escherichia coli in inclusion bodies, suggesting that this residue is involved with the tertiary structure or folding property of this enzyme. However, the I52A, S65A, R66A and M101A mutants were purified by glutathione affinity chromatography and the enzyme activity characterized. On the basis of steady-state kinetics, difference spectroscopy, unfolding and refolding studies, it was concluded that these residues: (1) contribute to the affinity of the GSH-binding site (‘G-site’) for GSH, (2) influence GSH thiol ionization, (3) participate in kcat regulation by affecting the rate-limiting step of the reaction, and in the case of Ile-52 and Arg-66, influenced structural integrity and/or folding of the enzyme. The structural perturbations from these mutants are probably transmitted to the hydrophobic-substrate-binding site (‘H-site’) through changes in active site topology or through effects on GSH orientation. Therefore these active site residues appear to contribute to various steps in the catalytic mechanism, as well as having an influence on the packing of the protein.

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