Key Catalytic Residues Research Articles

Expression, characterization and application of the deoxynivalenol dehydrogenase from Devosia yakushimensis.

Deoxynivalenol (DON) is one of the type-B trichothecene mycotoxins generally produced by Fusarium fungi and widely pollutes wheat and other grains, causing a great loss in grain yield and significant threat to human health. Enzymatic treatment of DON has displayed a significant role in controlling its levels in recent years. Here, the DON dehydrogenase from Devosia yakushimensis (DeDDH) is reported. DeDDH exhibited the highest activity in an environment of 35 °C and pH 7.5. In addition, the residual activity of DeDDH was about 40% after pre-incubation at 80 °C for 0.5 h, suggesting a good thermostability. The presence of Ca2+ significantly boosted the activity of DeDDH, but substituting Ca2+ with other ions could hardly retain the activity. At the optimal conditions, DeDDH efficiently degraded 75% DON (45 μg mL-1) within 4 h. Notably, when three cofactors, PQQ, PMS and DCPIP, were added together, more than 90% DON (45 μg mL-1) was quickly degraded in the first 40 min. The residues Thr485 and Leu521 were found to be significant to the activity of DeDDH by site-directed mutagenesis, much different from other DON dehydrogenases. Nevertheless, further research on the crystal structure determination of DeDDH, key catalytic residue identification, catalytic activity and thermostability modification still needs to be conducted for application in industry. © 2024 Society of Chemical Industry.

Exploring the competitive inhibition of α-glucosidase by citrus pectin enzymatic hydrolysate and its mechanism: An integrated experimental and simulation approach

The endo-polygalacturonase D (PgaD) from Aspergillus niger JL15 was recombinantly expressed in Escherichia coli BL21, exhibiting an optimal activity at 55 °C and pH 4.0. Hydrolysis products of citrus pectin by recombinant PgaD included galacturonic acid (GalA), digalacturonic acid (GalA2), trigalacturonic acid (GalA3), and tetragalacturonic acid (GalA4). The hydrolysates exhibited significant antioxidant capacity and dose-dependent competitive inhibition of α-glucosidase. GalA2 and GalA3 acted as competitive inhibitors of α-glucosidase, with inhibition constant of 0.0589 mmol.L−1 and 0.6732 mmol.L−1, respectively. Molecular dynamics (MD) simulations revealed that both GalA2 and GalA3 penetrated the catalytic pocket of α-glucosidase and formed stable hydrogen bonds with key catalytic residues D352 and D215. The binding free energies of GalA2-α-glucosidase and GalA3-α-glucosidase complexes were − 10.3 ± 0.6 kcal·mol−1 and -10.8 ± 0.7 kcal·mol−1, respectively. These findings might offer new ideas for the development of α-glucosidase inhibitors sourced from citrus pectin, as well as enhance utilization of the renewable plant polysaccharide resources.

Development of Tertiary Structure of Laccase from Geobacillus uzenensis using Homology Modelling

Laccases are a versatile enzyme with immense potential in various biotechnological applications. In this study, the protein structure prediction of laccase from Geobacillus uzenensis, a bacteria known for its robust enzymatic activity is focused. The protein structural elucidation of this laccase is crucial to understand its substrate binding and overall functionality. Protein structure can be determined by computational prediction, which is commonly known as homology modelling. The three-dimensional (3D) model was built based on the available crystal structures of related laccase enzymes and aligned with the primary sequence of the target protein. The resulting model exhibited a high degree of structural similarity and conservation of key catalytic residues, supporting its reliability for further analyses. Firstly, the suitable template was identified with 85.61% of sequence identity determined by sequence alignment. Then, MODELLER program was used to predict the model using the method of satisfaction of spatial restraints. The model was then analyzed for its quality by computational analysis tools such as Ramachandran's Plot. Finally, the binding site of the protein was identified using the GRaSP computational tool. These findings provide significant insight on comprehensive analysis of the laccase from G. uzenensis, by providing a structural framework to unravel its functional properties and substrate specificity.

Phylogenetic analysis and pathogenesis study of a new deletion mutation causing inherited FⅩ deficiency

Objective: To analyze the F10 gene mutations in a Chinese pedigree affected with the deficiency of the hereditary coagulation factor X (FX), resulting from a new deletion mutation, and to study the associated molecular pathogenesis. Methods: Next generation sequencing (NGS) was performed to screen the genetic mutations in the proband which were then verified by Sanger sequencing. The FX activity (FX∶C) of probands and their family members was detected using the blood clotting method, and the mutation sites of the family members were analyzed using Sanger sequencing. The pathogenicity of the mutation site was predicted by using the online bioinformatics software, Mutation Taster. The SWISS-MODEL software was used for stimulating the three-dimensional models of the wild-type and mutant proteins for analyzing the influence of the mutation site on the structure and function of the proteins, and for analyzing the difference between the catalytic residues of the wild-type and the mutant proteins. The level of the F10 gene mRNA was quantitatively analyzed by qRT-PCR (quantitative reverse transcription polymerase chain reaction) method by constructing plasmids, transfecting human embryonic kidney 293T cells (HEK 293T), and analyzing the splicing of the mutated site by RT-PCR method. The levels of FⅩ∶Ag in cell lysates and cell culture media (both inside and outside the cells) were detected by the ELISA (enzyme linked immunosorbent assay) method. Results: A medium-grade factor X deficiency with a 36.42% FⅩ∶C ratio was detected in the proband by the coagulation method. NGS analysis demonstrated a heterozygous deletion mutation in exon 8:c.902_919del (p.Ala301_Glu306del) in the proband. Sanger sequencing analysis indicated that some members of the family (mother and grandfather) were also carriers of the corresponding deletion mutation. Online bioinformatics software predicted the pathogenic nature of the c.902_919del mutation, with a pathogenic score of 0.999. The 3D protein structure model analysis indicated that the c.902_919del mutation resulted in the disappearance of a segment of β-fold in the protein structure, thereby shortening the preceding segment of the β-fold and a subsequent loss of hydrogen bonds between adjacent amino acids with no significant difference in the side chain conformation of the key catalytic residues compared to the wild-type. mRNA splicing analysis indicated the absence of alternative splicing changes in the mutation, and qRT-PCR results indicated the absence of a statistically significant difference between the mRNA levels of F10 gene and wild-type mRNA in cells expressing c.902_919del mutant. The ELISA results indicated that there was no statistically significant difference in the FX∶Ag levels of the mutant cell culture medium and the lysate. Conclusions: In this pedigree, the heterozygous mutation in exon 8 of F10 gene (c.902_919del, p.Ala301_Glu306del) caused the hereditary factor Ⅹ deficiency.

Structural insight into the function of human peptidyl arginine deiminase 6

Peptidyl arginine deiminase 6 (PADI6 or PAD6) is vital for early embryonic development in mice and humans, yet its function remains elusive. PADI6 is less conserved than other PADIs and it is currently unknown whether it has a catalytic function. Here we show that human PADI6 dimerises like hPADIs 2–4, however, does not bind Ca2+ and is inactive in in vitro assays against standard PADI substrates. By determining the crystal structure of hPADI6, we show that hPADI6 is structured in the absence of Ca2+ where hPADI2 and hPADI4 are not, and the Ca-binding sites are not conserved. Moreover, we show that whilst the key catalytic aspartic acid and histidine residues are structurally conserved, the cysteine is displaced far from the active site centre and the hPADI6 active site pocket appears closed through a unique evolved mechanism in hPADI6, not present in the other PADIs. Taken together, these findings provide insight into how the function of hPADI6 may differ from the other PADIs based on its structure and provides a resource for characterising the damaging effect of clinically significant PADI6 variants.

Biochemical and structural elucidation of the L-carnitine degradation pathway of the human pathogen Acinetobacter baumannii.

Acinetobacter baumannii is an opportunistic human pathogen which can use host-derived L-carnitine as sole carbon and energy source. Recently, an L-carnitine transporter (Aci1347) and a specific monooxygense (CntA/CntB) for the intracellular cleavage of L-carnitine have been characterized. Subsequent conversion of the resulting malic semialdehyde into the central metabolite L-malate was hypothesized. Alternatively, L-carnitine degradation via D-malate with subsequent oxidation into pyruvate was proposed. Here we describe the in vitro and in vivo reconstitution of the entire pathway, starting from the as yet uncharacterized gene products of the carnitine degradation gene operon. Using recombinantly purified enzymes, enantiomer-specific formation of D-malate by the NAD(P)+-dependent malic semialdehyde dehydrogenase (MSA-DH) is demonstrated. The solved X-ray crystal structure of tetrameric MSA-DH reveals the key catalytic residues Cys290 and Glu256, accessible through opposing substrate and cofactor funnels. Specific substrate binding is enabled by Arg166, Arg284 and Ser447 while dual cofactor specificity for NAD+ and NADP+ is mediated by Asn184. The subsequent conversion of the unusual D-malate reaction product by an uncharacterized NAD+-dependent malate dehydrogenase (MDH) is shown. Tetrameric MDH is a β-decarboxylating dehydrogenase that synthesizes pyruvate. MDH experiments with alternative substrates showed a high degree of substrate specificity. Finally, the entire A. baumannni pathway was heterologously reconstituted, allowing E. coli to grow on L-carnitine as a carbon and energy source. Overall, the metabolic conversion of L-carnitine via malic semialdehyde and D-malate into pyruvate, CO2 and trimethylamine was demonstrated. Trimethylamine is also an important gut microbiota-dependent metabolite that is associated with an increased risk of cardiovascular disease. The pathway reconstitution experiments allowed us to assess the TMA forming capacity of gut microbes which is related to human cardiovascular health.

An Enzymatic Oxidation Cascade Converts δ-Thiolactone Anthracene to Anthraquinone in the Biosynthesis of Anthraquinone-Fused Enediynes.

Anthraquinone-fused enediynes are anticancer natural products featuring a DNA-intercalating anthraquinone moiety. Despite recent insights into anthraquinone-fused enediyne (AQE) biosynthesis, the enzymatic steps involved in anthraquinone biogenesis remain to be elucidated. Through a combination of in vitro and in vivo studies, we demonstrated that a two-enzyme system, composed of a flavin adenine dinucleotide (FAD)-dependent monooxygenase (DynE13) and a cofactor-free enzyme (DynA1), catalyzes the final steps of anthraquinone formation by converting δ-thiolactone anthracene to hydroxyanthraquinone. We showed that the three oxygen atoms in the hydroxyanthraquinone originate from molecular oxygen (O2), with the sulfur atom eliminated as H2S. We further identified the key catalytic residues of DynE13 and A1 by structural and site-directed mutagenesis studies. Our data support a catalytic mechanism wherein DynE13 installs two oxygen atoms with concurrent desulfurization and decarboxylation, whereas DynA1 acts as a cofactor-free monooxygenase, installing the final oxygen atom in the hydroxyanthraquinone. These findings establish the indispensable roles of DynE13 and DynA1 in AQE biosynthesis and unveil novel enzymatic strategies for anthraquinone formation.

Structural characterization of ligand binding and pH-specific enzymatic activity of mouse Acidic Mammalian Chitinase

Chitin is an abundant biopolymer and pathogen-associated molecular pattern that stimulates a host innate immune response. Mammals express chitin-binding and chitin-degrading proteins to remove chitin from the body. One of these proteins, Acidic Mammalian Chitinase (AMCase), is an enzyme known for its ability to function under acidic conditions in the stomach but is also active in tissues with more neutral pHs, such as the lung. Here, we used a combination of biochemical, structural, and computational modeling approaches to examine how the mouse homolog (mAMCase) can act in both acidic and neutral environments. We measured kinetic properties of mAMCase activity across a broad pH range, quantifying its unusual dual activity optima at pH 2 and 7. We also solved high-resolution crystal structures of mAMCase in complex with oligomeric GlcNAcn, the building block of chitin, where we identified extensive conformational ligand heterogeneity. Leveraging these data, we conducted molecular dynamics simulations that suggest how a key catalytic residue could be protonated via distinct mechanisms in each of the two environmental pH ranges. These results integrate structural, biochemical, and computational approaches to deliver a more complete understanding of the catalytic mechanism governing mAMCase activity at different pH. Engineering proteins with tunable pH optima may provide new opportunities to develop improved enzyme variants, including AMCase, for therapeutic purposes in chitin degradation.

Structural characterization of ligand binding and pH-specific enzymatic activity of mouse Acidic Mammalian Chitinase.

Chitin is an abundant biopolymer and pathogen-associated molecular pattern that stimulates a host innate immune response. Mammals express chitin-binding and chitin-degrading proteins to remove chitin from the body. One of these proteins, Acidic Mammalian Chitinase (AMCase), is an enzyme known for its ability to function under acidic conditions in the stomach but is also active in tissues with more neutral pHs, such as the lung. Here, we used a combination of biochemical, structural, and computational modeling approaches to examine how the mouse homolog (mAMCase) can act in both acidic and neutral environments. We measured kinetic properties of mAMCase activity across a broad pH range, quantifying its unusual dual activity optima at pH 2 and 7. We also solved high-resolution crystal structures of mAMCase in complex with oligomeric GlcNAcn, the building block of chitin, where we identified extensive conformational ligand heterogeneity. Leveraging these data, we conducted molecular dynamics simulations that suggest how a key catalytic residue could be protonated via distinct mechanisms in each of the two environmental pH ranges. These results integrate structural, biochemical, and computational approaches to deliver a more complete understanding of the catalytic mechanism governing mAMCase activity at different pH. Engineering proteins with tunable pH optima may provide new opportunities to develop improved enzyme variants, including AMCase, for therapeutic purposes in chitin degradation.

The role of Tyr34 in proton-coupled electron transfer of human manganese superoxide dismutase.

Human manganese superoxide dismutase (MnSOD) plays a crucial role in controlling levels of reactive oxygen species (ROS) by converting superoxide (O2 ●-) to molecular oxygen (O2) and hydrogen peroxide (H2O2) with proton-coupled electron transfers (PCETs). The reactivity of human MnSOD is determined by the state of a key catalytic residue, Tyr34, that becomes post-translationally inactivated by nitration in various diseases associated with mitochondrial dysfunction. We previously reported that Tyr34 has an unusual pKa due to its proximity to the Mn metal and undergoes cyclic deprotonation and protonation events to promote the electron transfers of MnSOD. To shed light on the role of Tyr34 MnSOD catalysis, we performed neutron diffraction, X-ray spectroscopy, and quantum chemistry calculations of Tyr34Phe MnSOD in various enzymatic states. The data identifies the contributions of Tyr34 in MnSOD activity that support mitochondrial function and presents a thorough characterization of how a single tyrosine modulates PCET catalysis.

The unusual kinetics of lactate dehydrogenase of Schistosoma mansoni and their role in the rapid metabolic switch after penetration of the mammalian host

Lactate dehydrogenase (LDH) from Schistosoma mansoni has peculiar properties for a eukaryotic LDH. Schistosomal LDH (SmLDH) isolated from schistosomes, and the recombinantly expressed protein, are strongly inhibited by ATP, which is neutralized by fructose-1,6-bisphosphate (FBP). In the conserved FBP/anion binding site we identified two residues in SmLDH (Val187 and Tyr190) that differ from the conserved residues in LDHs of other eukaryotes, but are identical to conserved residues in FBP-sensitive prokaryotic LDHs. Three-dimensional (3D) models were generated to compare the structure of SmLDH with other LDHs. These models indicated that residues Val187, and especially Tyr190, play a crucial role in the interaction of FBP with the anion pocket of SmLDH. These 3D models of SmLDH are also consistent with a competitive model of SmLDH inhibition in which ATP (inhibitor) and FBP (activator) compete for binding in a well-defined anion pocket. The model of bound ATP predicts a distortion of the nearby key catalytic residue His195, resulting in enzyme inhibition. To investigate a possible physiological role of this allosteric regulation of LDH in schistosomes we made a kinetic model in which the allosteric regulation of the glycolytic enzymes can be varied. The model showed that inhibition of LDH by ATP prevents fermentation to lactate in the free-living stages in water and ensures complete oxidation via the Krebs cycle of the endogenous glycogen reserves. This mechanism of allosteric inhibition by ATP prevents the untimely depletion of these glycogen reserves, the only fuel of the free-living cercariae. Neutralization by FBP of this ATP inhibition of LDH prevents accumulation of glycolytic intermediates when S. mansoni schistosomula are confronted with the sudden large increase in glucose availability upon penetration of the final host. It appears that the LDH of S. mansoni is special and well suited to deal with the variations in glucose availability the parasite encounters during its life cycle.

Network of epistatic interactions in an enzyme active site revealed by large-scale deep mutational scanning

Cooperative interactions between amino acids are critical for protein function. A genetic reflection of cooperativity is epistasis, which is when a change in the amino acid at one position changes the sequence requirements at another position. To assess epistasis within an enzyme active site, we utilized CTX-M β-lactamase as a model system. CTX-M hydrolyzes β-lactam antibiotics to provide antibiotic resistance, allowing a simple functional selection for rapid sorting of modified enzymes. We created all pairwise mutations across 17 active site positions in the β-lactamase enzyme and quantitated the function of variants against two β-lactam antibiotics using next-generation sequencing. Context-dependent sequence requirements were determined by comparing the antibiotic resistance function of double mutations across the CTX-M active site to their predicted function based on the constituent single mutations, revealing both positive epistasis (synergistic interactions) and negative epistasis (antagonistic interactions) between amino acid substitutions. The resulting trends demonstrate that positive epistasis is present throughout the active site, that epistasis between residues is mediated through substrate interactions, and that residues more tolerant to substitutions serve as generic compensators which are responsible for many cases of positive epistasis. Additionally, we show that a key catalytic residue (Glu166) is amenable to compensatory mutations, and we characterize one such double mutant (E166Y/N170G) that acts by an altered catalytic mechanism. These findings shed light on the unique biochemical factors that drive epistasis within an enzyme active site and will inform enzyme engineering efforts by bridging the gap between amino acid sequence and catalytic function.

Synthesis of novel hydrazide Schiff bases with anti-diabetic and anti-hyperlipidemic effects: in-vitro, in-vivo and in-silico approaches

The increasing global incidence of non-insulin-dependent diabetes mellitus (NIDDM) necessitates innovative therapeutic solutions. This study focuses on the design, synthesis and biological evaluation of Schiff base derivatives from 2-bromo-2-(2-chlorophenyl) acetic acid, particularly hydrazone compounds 4a and 4b. Both in-vitro and in-vivo assays demonstrate these derivatives’ strong antidiabetic and anti-hyperlipidemic properties. In a 15-d experiment, we administered 4a and 4b at doses of 2.5 and 5 mg/kg body weight, which effectively improved symptoms of alloxan-induced diabetes in mice. These symptoms included weight loss, increased water consumption and high blood glucose levels. The compounds also normalized abnormal levels of total cholesterol (TC), triacylglycerol (TG) and low-density lipoprotein cholesterol (LDL-C), while raising the levels of high-density lipoprotein cholesterol (HDLC). Computational analysis showed that these compounds effectively inhibited the α-glucosidase enzyme by interacting with key catalytic residues, specifically Asp214 and Asp349. These computational results were confirmed through in-vitro tests, where 4a and 4b showed strong α-glucosidase inhibitory activity, with IC50 values of 0.70 ± 0.11 and 10.29 ± 0.30 µM, respectively. These compounds were more effective than the standard drug, acarbose, which had an IC50 value of 873.34 ± 1.67 µM. Mechanistic studies further indicated competitive inhibition, reinforcing the therapeutic potential of 4a and 4b for NIDDM treatment. Communicated by Ramaswamy H. Sarma

Exploring the potential of nutraceutical to combat gliomas: focus on mIDH2 protein

Somatic transformations in the key catalytic residues of the Isocitrate Dehydrogenase (IDH) enzyme assist in the onset of distinct malignancies including glioma. Currently, enasidenib is the FDA-approved drug used to target IDH2 protein. However, the use of enasidenib as a plausible mIDH2 inhibitor is constrained by poor brain penetrating capability and dose-limiting toxicity. Thus, the present study aimed to explore the potential of nutraceuticals to synergistically elevate the efficacy of the existing drugs available for glioma management. The binding affinity and free energy of the nutraceuticals were evaluated using molecular docking and MM-GBSA analysis. The resultant 14 compounds were subjected to machine learning-based rescoring strategies to distinguish binders from nonbinders. The pharmacokinetic and toxicity analysis was also implemented alongside virtual cell line assay. The results of our study identified DB14002 (D-alpha-Tocopherol acetate, analog of Vitamin E) as the potential hit compound with appreciable binding affinity, brain penetrating capability and antineoplastic activity against glioma cell lines. In the end, the conformational stability and dynamic characteristics of DB14002 were examined for a stipulated time frame of 250ns. Indeed, the outcomes of our study culminate the use of DB14002 as a synergistic drug-like candidate which could be translated as a plausible inhibitor of mIDH2 in the forthcoming years.

Bacterial selenocysteine synthase structure revealed by single-particle cryoEM

The 21st amino acid, selenocysteine (Sec), is synthesized on its dedicated transfer RNA (tRNASec). In bacteria, Sec is synthesized from Ser-tRNA[Ser]Sec by Selenocysteine Synthase (SelA), which is a pivotal enzyme in the biosynthesis of Sec. The structural characterization of bacterial SelA is of paramount importance to decipher its catalytic mechanism and its role in the regulation of the Sec-synthesis pathway. Here, we present a comprehensive single-particle cryo-electron microscopy (SPA cryoEM) structure of the bacterial SelA with an overall resolution of 2.69 Å. Using recombinant Escherichia coli SelA, we purified and prepared samples for single-particle cryoEM. The structural insights from SelA, combined with previous in vivo and in vitro knowledge, underscore the indispensable role of decamerization in SelA's function. Moreover, our structural analysis corroborates previous results that show that SelA adopts a pentamer of dimers configuration, and the active site architecture, substrate binding pocket, and key K295 catalytic residue are identified and described in detail. The differences in protein architecture and substrate coordination between the bacterial enzyme and its counterparts offer compelling structural evidence supporting the independent molecular evolution of the bacterial and archaea/eukarya Ser-Sec biosynthesis present in the natural world.

Inhibitory potential of furanocoumarins against cyclin dependent kinase 4 using integrated docking, molecular dynamics and ONIOM methods

Cyclin Dependent Kinase 4 (CDK4) is vital in the process of cell-cycle and serves as a G1 phase checkpoint in cell division. Selective antagonists of CDK4 which are in use as clinical chemotherapeutics cause various side-effects in patients. Furanocoumarins induce anti-cancerous effects in a range of human tumours. Therefore, targeting these compounds against CDK4 is anticipated to enhance therapeutic effectiveness. This work intended to explore the CDK4 inhibitory potential of 50 furanocoumarin molecules, using a comprehensive approach that integrates the processes of docking, drug-likeness, pharmacokinetic analysis, molecular dynamics simulations and ONIOM (Our own N-layered Integrated molecular Orbital and Molecular mechanics) methods. The top five best docked compounds obtained from docking studies were screened for subsequent analysis. The molecules displayed good pharmacokinetic properties and no toxicity. Epoxybergamottin, dihydroxybergamottin and notopterol were found to inhabit the ATP-binding zone of CDK4 with substantial stability and negative binding free energy forming hydrogen bonds with key catalytic residues of the protein. Notopterol exhibiting the highest binding energy was subjected to ONIOM calculations wherein the hydrogen bonding interactions were retained with significant negative interaction energy. Hence, through these series of computerised methods, notopterol was screened as a potent CDK4 inhibitor and can act as a starting point in successive processes of drug design. Communicated by Ramaswamy H. Sarma

Biosynthesis of 4-Acyl-5-aminoimidazole Alkaloids Featuring a New Friedel-Crafts Acyltransferase.

Friedel-Crafts acylation (FCA) is a highly beneficial approach in organic chemistry for creating the important C-C bonds that are necessary for building intricate frameworks between aromatic substrates and an acyl group. However, there are few reports about enzyme catalyzed FCA reactions. In this study, 4-acyl-5-aminoimidazole alkaloids (AAIAs), streptimidazoles A-C (1-3), and the enantiopure (+)-nocarimidazole C (4) as well as their ribosides, streptimidazolesides A-D (5-8), were identified from the fermentation broth of Streptomyces sp. OUCMDZ-944 or heterologous S. coelicolor M1154 mutant. The biosynthetic gene cluster (smz) was identified, and the biosynthetic pathway of AAIAs was elucidated for the first time. In vivo and in vitro studies proved the catalytic activity of the four essential genes smzB, -C, -E, and -F for AAIAs biosynthesis and clarified the biosynthetic process of the alkaloids. The ligase SmzE activates fatty acyl groups and connects them to the acyl carrier protein (ACP) holo-SmzF. Then, the acyl group is transferred onto the key residue Cys49 of SmzB, a new Friedel-Crafts acyltransferase (FCase). Subsequently, the FCA reaction between the acyl groups and 5-aminoimidazole ribonucleotide (AIR) occurs to generate the key intermediate AAIA-nucleotides catalyzed by SmzB. Finally, the hydrolase SmzC catalyzes the N-glycosidic bond cleavage of the intermediates to form AAIAs. Structural simulation, molecular modeling, and mutational analysis of SmzB showed that Tyr26, Cys49, and Tyr93 are the key catalytic residues in the C-C bond formation of the acyl chain of AAIAs, providing mechanistic insights into the enzymatic FCA reaction.

Identifying potential compounds from Bacopa monnieri (brahmi) against coxsackievirus A16 RdRp targeting HFM disease (tomato flu)

Hand, foot, and mouth disease (HFMD), primarily instigated by Coxsackievirus A16 (CVA16), poses a serious health concern, necessitating effective therapeutic interventions. The RNA-dependent RNA polymerase (RdRp) of CVA16 emerges as a promising drug target for HFMD treatment. This study presents an in-silico pipeline for the identification of potential RdRp inhibitors against CVA16. A library of 91 natural compounds derived from Bacopa monnieri (brahmi) was virtually screened against the CVA16 RdRp. Here, Bacobitacin D emerged as a promising hit molecule, forming 8 hydrogen bonds including key catalytic site residues (Asp238 and Asp329) within the RdRp active site. Further, molecular dynamics (MD) simulations and MM/GBSA binding free energy calculations was applied on the top three hits that were selected based on exhaustive docking scores (≤−9.55 ​kcal/mol). Bacobitacin D exhibited sustainable stability, as evidenced by minimal deviation (RMSD ​= ​0.75 ​± ​0.02 ​nm) during a 100 ns MD simulation. Importantly, Bacopaside IV exhibited the lowest ΔGTOTAL binding free energy (−23.70 ​kcal/mol), while Bacobitacin D displayed a comparable ΔGTOTAL of −19.14 ​kcal/mol. Structural interpretation of the most populated cluster derived from MD simulations showed direct interactions of Bacobitacin D with pivotal catalytic residues, including Asp238 and Ser289. This comprehensive study confirmed Bacobitacin D as a potent inhibitor of CVA16 RdRp, offering a potential avenue for therapeutic intervention against HFMD. Experimental validation is required to confirm the inhibitory action of Bacobitacin D against HFMD.

Two O-methyltransferases are responsible for multiple O-methylation steps in the biosynthesis of furanocoumarins from Angelicadecursiva

Angelica decursiva, an important traditional medicinal plant, possesses a unique pharmacological activity. Its principal active ingredients are coumarins, including scopoletin, bergapten, and imperatorin. However, the enzymes catalyzing the critical step of coumarins biosynthesis pathway remain unidentified. This study initially screened 14 candidate O-methyltransferases (OMTs) through transcriptomics and metabolic determination. Combined with gene expression profile and biochemical assays, two OMTs (AdOMT1 and AdOMT2) were identified to be responsible for the O-methylation of coumarins in A. decursiva. AdOMT1 showed higher catalytic efficiency for bergaptol (Kcat/Km = 3123.70), while AdOMT2 exhibited higher substrate and catalytic promiscuity, allowing it to catalyze the methylation of various coumarins, phenylpropanes, and flavonoids. Based on molecular docking and site-specific mutagenesis determined that His126/Asn132, Phe171/Phe177, Trp261/Trp267, and Asn312/Ile317 were the key catalytic residues of AdOMT1 and AdOMT2 for the O-methylation of bergaptol and xanthotoxol. Further phylogenetic analysis confirmed the reasons for the catalytic functional differentiation of AdOMT1 and AdOMT2. This study provides a basis for exploring the coumarins O-methylation mechanism and plays a critical role in diversifying the structures used in coumarins drug discovery.

Uracil-DNA glycosylase of murine gammaherpesvirus 68 binds cognate viral replication factors independently of its catalytic residues.

Herpesviruses are large double-stranded DNA viruses that encode core replication proteins and accessory factors involved in nucleotide metabolism and DNA repair. Mammalian uracil-DNA glycosylases (UNG) excise deleterious uracil residues from their genomic DNA. Each herpesvirus UNG studied to date has demonstrated conservation of the enzymatic function to excise uracil residues from DNA. We previously reported that a murine gammaherpesvirus (MHV68) with a stop codon in ORF46 (ORF46.stop) that encodes for vUNG was defective in lytic replication and latency in vivo. However, a mutant virus that expressed a catalytically inactive vUNG (ORF46.CM) had no replication defect unless coupled with additional mutations in the catalytic motif of the viral dUTPase (ORF54.CM). The disparate phenotypes observed in the vUNG mutants led us to explore the non-enzymatic properties of vUNG. Immunoprecipitation of vUNG followed by mass spectrometry in MHV68-infected fibroblasts identified a complex comprising the cognate viral DNA polymerase, vPOL, encoded by ORF9, and the viral DNA polymerase processivity factor, vPPF, encoded by ORF59. MHV68 vUNG co-localized with vPOL and vPPF in subnuclear structures consistent with viral replication compartments. In reciprocal co-immunoprecipitations, the vUNG formed a complex with the vPOL and vPPF upon transfection with either factor alone or in combination. Lastly, we determined that key catalytic residues of vUNG are not required for interactions with vPOL and vPPF upon transfection or in the context of infection. We conclude that the vUNG of MHV68 associates with vPOL and vPPF independently of its catalytic activity. IMPORTANCE Gammaherpesviruses encode a uracil-DNA glycosylase (vUNG) that is presumed to excise uracil residues from viral genomes. We previously identified the vUNG enzymatic activity, but not the protein itself, as dispensable for gammaherpesvirus replication in vivo. In this study, we report a non-enzymatic role for the viral UNG of a murine gammaherpesvirus in forming a complex with two key components of the viral DNA replication machinery. Understanding the role of the vUNG in this viral DNA replication complex may inform the development of antiviral drugs that combat gammaherpesvirus-associated cancers.