3D-QSAR and molecular docking studies of peptide-hybrids as dengue virus NS2B/NS3 protease inhibitors.

Global warming and climate change have made dengue disease a global health issue. More than 50 % of the world's population is at danger of dengue virus (DENV) infection, according to the World Health Organization (WHO). Therefore, a clinically approved dengue fever vaccination and effective treatment are needed. Peptide medication development is new pharmaceutical research. Here we intend to recognize the structural features inhibiting the DENV NS2B/NS3 serine protease for a series of peptide-hybrid inhibitors (R1-R2-Lys-R3-NH2) by the 3D-QSAR technique. Comparative molecular field analysis (q2 = 0.613, r2 = 0.938, r2pred = 0.820) and comparative molecular similarity indices analysis (q2 = 0.640, r2 = 0.928, r2pred = 0.693) were established, revealing minor, electropositive, H-bond acceptor groups at the R1 position, minor, electropositive, H-bond donor groups at the R2 position, and bulky, hydrophobic groups at the R3 position for higher inhibitory activity. Docking studies revealed extensive H-bond and hydrophobic interactions in the binding of tripeptide analogues to the NS2B/NS3 protease. This study provides an insight into the key structural features for the design of peptide-based inhibitors of DENV NS2B/NS3 protease.

Signal Propagation in the ATPase Domain of Mycobacterium tuberculosis DNA Gyrase from Dynamical-Nonequilibrium Molecular Dynamics Simulations.

DNA gyrases catalyze negative supercoiling of DNA, are essential for bacterial DNA replication, transcription, and recombination, and are important antibacterial targets in multiple pathogens, including Mycobacterium tuberculosis, which in 2021 caused >1.5 million deaths worldwide. DNA gyrase is a tetrameric (A2B2) protein formed from two subunit types: gyrase A (GyrA) carries the breakage-reunion active site, whereas gyrase B (GyrB) catalyzes ATP hydrolysis required for energy transduction and DNA translocation. The GyrB ATPase domains dimerize in the presence of ATP to trap the translocated DNA (T-DNA) segment as a first step in strand passage, for which hydrolysis of one of the two ATPs and release of the resulting inorganic phosphate is rate-limiting. Here, dynamical-nonequilibrium molecular dynamics (D-NEMD) simulations of the dimeric 43 kDa N-terminal fragment of M. tuberculosis GyrB show how events at the ATPase site (dissociation/hydrolysis of bound nucleotides) are propagated through communication pathways to other functionally important regions of the GyrB ATPase domain. Specifically, our simulations identify two distinct pathways that respectively connect the GyrB ATPase site to the corynebacteria-specific C-loop, thought to interact with GyrA prior to DNA capture, and to the C-terminus of the GyrB transduction domain, which in turn contacts the C-terminal GyrB topoisomerase-primase (TOPRIM) domain responsible for interactions with GyrA and the centrally bound G-segment DNA. The connection between the ATPase site and the C-loop of dimeric GyrB is consistent with the unusual properties of M. tuberculosis DNA gyrase relative to those from other bacterial species.

Combining Deep Learning and Structural Modeling to Identify Potential Acetylcholinesterase Inhibitors from Hericium erinaceus.

Alzheimer's disease (AD) is the most common type of dementia, affecting over 50 million people worldwide. Currently, most approved medications for AD inhibit the activity of acetylcholinesterase (AChE), but these treatments often come with harmful side effects. There is growing interest in the use of natural compounds for disease prevention, alleviation, and treatment. This trend is driven by the anticipation that these substances may incur fewer side effects than existing medications. This research presents a computational approach combining machine learning with structural modeling to discover compounds from medicinal mushrooms with a high potential to inhibit the activity of AChE. First, we developed a deep neural network capable of rapidly screening a vast number of compounds to indicate their potential to inhibit AChE activity. Subsequently, we applied deep learning models to screen the compounds in the BACMUSHBASE database, which catalogs the bioactive compounds from cultivated and wild mushroom varieties local to Thailand, resulting in the identification of five promising compounds. Next, the five identified compounds underwent molecular docking techniques to calculate the binding energy between the compounds and AChE. This allowed us to refine the selection to two compounds, erinacerin A and hericenone B. Further analysis of the binding energy patterns between these compounds and the target protein revealed that both compounds displayed binding energy profiles similar to the combined characteristics of donepezil and galanthamine, the prescription drugs for AD. We propose that these two compounds, derived from Hericium erinaceus (also known as lion's mane mushroom), are suitable candidates for further research and development into symptom-alleviating AD medications.

Synthesis, Antiacetylcholinesterase Activity, and Molecular Dynamics Simulation of Aporphine-benzylpyridinium Conjugates.

A series of aporphines conjugated with an N-benzylpyridinium moiety through an amide-bond linkage were synthesized and evaluated for their acetylcholinesterase (AChE) inhibitory activity. The conjugation of the N-benzylpyridinium group significantly enhanced the AChE inhibitory activity of the core aporphine. The halogen substituents on the benzyl group affected the activity of the conjugates. Both (S)- and (R)-enantiomers of three conjugates with low IC50 values were synthesized and evaluated for their activities. All (S)-enantiomers exhibited higher activity than the corresponding (R)-enantiomers. The (S)-enantiomer of 2-chlorobenzylpyridinium-containing aporphine was the most potent inhibitor in this study with an IC50 value of 0.06 ± 0.003 µM. Molecular dynamics simulation analysis revealed that both enantiomers can interact with the AChE binding site, whereas the (S)-enantiomer possessed slightly stronger interaction than the (R)-enantiomer, presumably because of their different orientations, as evidenced by molecular docking. The N-benzylpyridinium dehydroaporphine conjugates were also synthesized but were less active than the corresponding aporphine conjugates.

Combined Deep Learning and Molecular Modeling Techniques on the Virtual Screening of New mTOR Inhibitors from the Thai Mushroom Database.

The mammalian target of rapamycin (mTOR) is a protein kinase of the PI3K/Akt signaling pathway that regulates cell growth and division and is an attractive target for cancer therapy. Many reports on finding alternative mTOR inhibitors available in a database contain a mixture of active compound data with different mechanisms, which results in an increased complexity for training the machine learning models based on the chemical features of active compounds. In this study, a deep learning model supported by principal component analysis (PCA) and structural methods was used to search for an alternative mTOR inhibitor from mushrooms. The mTORC1 active compound data set from the PubChem database was first filtered for only the compounds resided near the first-generation inhibitors (rapalogs) within the first two PCA coordinates of chemical features. A deep learning model trained by the filtered data set captured the main characteristics of rapalogs and displayed the importance of steroid cores. After that, another layer of virtual screening by molecular docking calculations was performed on ternary complexes of FKBP12-FRB domains and six compound candidates with high "active" probability scores predicted by the deep learning models. Finally, all-atom molecular dynamics simulations and MMPBSA binding energy analysis were performed on two selected candidates in comparison to rapamycin, which confirmed the importance of ring groups and steroid cores for interaction networks. Trihydroxysterol from Lentinus polychrous Lev. was predicted as an interesting candidate due to the small but effective interaction network that facilitated FKBP12-FRB interactions and further stabilized the ternary complex.

Elucidation of benzene sulfonamide derivative binding at a novel interprotomer pocket of wild type and mutants of coxsackievirus B3 viral capsid using molecular dynamics simulations and density functional theory.

Coxsackievirus B3 (CVB3), a serotype of enterovirus B, causes hand, foot, and mouth disease; pericarditis; and myocarditis. A benzene sulfonamide derivative is reported to have inhibitory activity against wild-type (WT) and eight mutants of the viral capsid of CVB3. Furthermore, the crystal structure of the complex formed between WT viral capsid of CVB3 and the derivative revealed binding at a novel druggable interprotomer pocket. We investigated how the compound could be a potent inhibitor of both WT and some mutants of CVB3 by determining binding to the viral capsid and the interaction energy with the binding pocket based on molecular dynamics simulations and density functional theory. We found that hydrogen bonds, pi-pi interactions, and electrostatic interactions are the key interactions with a protomer unit of CVB3 viral capsid. The residual interaction energy determined using density functional theory revealed key binding with VP1:Arg234 and a residue in the nearby VP1 unit (VP1':Arg219). These results explain why the compound is still a potent inhibitor against eight mutants. Moreover, the decreased inhibitory activity for some mutants could be explained by the calculated binding energy and the highest occupied molecular orbital and lowest unoccupied molecular orbital energy. The results will be helpful for the development of drugs resistant to CVB3.

Structural basis for inhibition of a GH116 ß-glucosidase and its missense mutants by GBA2 inhibitors: Crystallographic and quantum chemical study.

The crystal structure of the Thermoanaerobacterium xylanolyticum in glycoside hydrolase family 116 (TxGH116) ß-glucosidase provides a structural model for human GBA2 glucosylceramidase, an enzyme defective in hereditary spastic paraplegia and a potential therapeutic target for treating Gaucher disease. To assess the therapeutic potential of known inhibitors, the X-ray structure of TxGH116 in complex with isofagomine (IFG) was determined at 2.0 Å resolution and showed the IFG bound in a relaxed chair conformation. The binding of IFG and 7 other iminosugar inhibitors to wild-type and mutant enzymes (Asp508His and Arg786His) mimicking GBA2 pathogenic variants was then evaluated computationally by two-layered ONIOM calculations (at the B3LYP:PM7 level). Calculations showed that six charged residues, Glu441, Asp452, His507, Asp593, Glu777, and Arg786 influence inhibitor binding most. His507, Glu777 and Arg786, form strong hydrogen bonds with the inhibitors (∼1.4-1.6 Å). Thus, the missense mutation of one of these residues in Arg786His has a greater effect on the interaction energies for all inhibitors compared to Asp508His. In line with the experimental data for the inhibitors that have been tested, the favorable interaction energy between the inhibitors and the TxGH116 protein followed the trend: isofagomine > 1-deoxynojirimycin > glucoimidazole > N-butyl-deoxynojirimycin ≈ N-nonyl-deoxynojirimycin > conduritol B epoxide ≈ azepane 1 > azepane 2. The obtained structural and energetic properties and comparison to the GBA2 model can lead to understanding of structural requirement for inhibitor binding in GH116 to aid the design of high potency GBA2 inhibitors.

Bioisosteric Design Identifies Inhibitors of Mycobacterium tuberculosis DNA Gyrase ATPase Activity.

Mutations in DNA gyrase confer resistance to fluoroquinolones, second-line antibiotics for Mycobacterium tuberculosis infections. Identification of new agents that inhibit M. tuberculosis DNA gyrase ATPase activity is one strategy to overcome this. Here, bioisosteric designs using known inhibitors as templates were employed to define novel inhibitors of M. tuberculosis DNA gyrase ATPase activity. This yielded the modified compound R3-13 with improved drug-likeness compared to the template inhibitor that acted as a promising ATPase inhibitor against M. tuberculosis DNA gyrase. Utilization of compound R3-13 as a virtual screening template, supported by subsequent biological assays, identified seven further M. tuberculosis DNA gyrase ATPase inhibitors with IC50 values in the range of 0.42-3.59 µM. The most active compound 1 showed an IC50 value of 0.42 µM, 3-fold better than the comparator ATPase inhibitor novobiocin (1.27 µM). Compound 1 showed noncytotoxicity to Caco-2 cells at concentrations up to 76-fold higher than its IC50 value. Molecular dynamics simulations followed by decomposition energy calculations identified that compound 1 occupies the binding pocket utilized by the adenosine group of the ATP analogue AMPPNP in the M. tuberculosis DNA gyrase GyrB subunit. The most prominent contribution to the binding of compound 1 to M. tuberculosis GyrB subunit is made by residue Asp79, which forms two hydrogen bonds with the OH group of this compound and also participates in the binding of AMPPNP. Compound 1 represents a potential new scaffold for further exploration and optimization as a M. tuberculosis DNA gyrase ATPase inhibitor and candidate anti-tuberculosis agent.

Structural analysis of the coronavirus main protease for the design of pan-variant inhibitors.

With the rapid rate of SARS-CoV-2 Main protease (Mpro) structures deposition, a computational method that can combine all the useful structural features becomes crucial. This research focuses on the frequently occurring atoms and residues to find a generalized strategy for inhibitor design given a large amount of protein complexes from SARS-CoV in contrast to SARS-CoV-2 Mpro. By superposing large numbers of the ligands onto the protein template and grid box, we can analyse which part of the structure is conserved from position-specific interaction for both data sets for the development of pan-Mpro antiviral design. The difference in conserved recognition sites from the crystal structures can be used to determine specificity determining residues for designing selective drugs. We can display pictures of the imaginary shape of the ligand by unionising all atoms from the ligand. We also pinpoint the most probable atom adjustments to imitate the frequently found densities from the ligand atoms statistics. With molecular docking, Molecular Dynamics simulation, and MM-PBSA methods, a carbonyl replacement at the nitrile warhead (N5) of Paxlovid's Nirmatrelvir (PF-07321332) was suggested. By gaining insights into the selectivity and promiscuity regions for proteins and ligands, crucial residues are highlighted, and the antiviral design strategies are proposed.

Key interactions of pyrimethamine derivatives specific to wild-type and mutant P. falciparum dihydrofolate reductase based on 3D-QSAR, MD simulations and quantum chemical calculations.

Plasmodium falciparum dihydrofolate reductase-thymidylate synthase (PfDHFR-TS) is an important target enzyme in malarial chemotherapy. An understanding of how novel inhibitors interact with wild-type (wtPfDHFR), quadruple-mutant (qmPfDHFR), and human (hDHFR) enzymes is required for the development of these compounds as antimalarials. This study is focused on a series of des-Cl and m-Cl phenyl analogs of pyrimethamine with various flexible 6-substituents. The interactions of these compounds with DHFR enzymes were investigated by 3 D-QSAR, MD simulations, MM-PBSA, and DFT calculations. CoMFA and CoMSIA models were developed with good predictive abilities for wtPfDHFR and qmPfDHFR. For hDHFR, CoMSIA models combined with clogP descriptor were successfully derived. Binding free energy using MM-PBSA and comparison of per residue decomposition energy analyses with the DFT method at M06-2X/6-31G ++(d,p) level of theory indicated that Asp54 and Phe58 play important roles in the binding of the most potent compound in the series (compound 27) with both wtPfDHFR and qmPfDHFR, whereas Arg59 and Arg122 were additionally found to interact with this inhibitor in qmPfDHFR. For hDHFR, the residues Glu30 and Phe34 but not Arg70, equivalent to Asp54, Phe58, and Arg122 in PfDHFR, also play role in compound 27 binding through strong hydrophobic interactions (Phe34) and hydrogen bond network with Glu30, Ile7, and Val115. From the key interactions identified in the DHFR-inhibitor complexes, a general scheme is proposed for designing new inhibitors selective for PfDHFR that is important for the development of novel antifolate antimalarials.Communicated by Ramaswamy H. Sarma.

Roles of hybrid donepezil scaffolds as potent human acetylcholinesterase inhibitors using in silico interaction analysis, drug-likeness, and pharmacokinetics prediction.

Acetylcholinesterase (AChE) is currently one of the potent targets for the treatment of Alzheimer's disease (AD). The discovery of promising new AChE inhibitors using a hybridisation method is considered as one of the effective strategies to overcome AD. In this study, potent hybrid donepezils previously reported as AChE inhibitors were investigated to gain an insight into the key binding interaction of their scaffolds, using molecular docking, molecular dynamics simulations and quantum chemical calculations. The results indicated that the key interactions found in both donepezil and the selected hybrid donepezils were the π-π interaction to Trp86 in the catalytic anionic site (CAS) and Trp286 and Tyr341 in the peripheral anionic site (PAS) in the AChE binding pocket. Moreover, the modification of the scaffolds revealed the adaptation of the orientation in the binding pocket and additional important interactions from the modified scaffold, such as H-bond and H-π interactions to Asp74, Tyr124 and Tyr337. In addition, the HOMO-LUMO prediction indicated the binding interaction by considering the electron transfer between the hybrid donepezils and key residues, such as Trp86 and Trp286. The bioavailability, drug-likeness and pharmacokinetics predictions confirmed the suitability of the hybrid donepezils for AD drug development. Most of the selected hybrid donepezils revealed good bioavailability, drug-likeness properties and pharmacokinetics; however, some need improved pharmacokinetic properties. The obtained information highlights the significance of the scaffold from the hybridisation method, which will be helpful for AD drug design and development in the future.

In silico multiscale drug design to discover key structural features of potential JAK2 inhibitors.

Background: JAK2 inhibitors have been proposed as a new therapeutic option for thalassemia therapy. The objective of this study was to discover the key structural features for improving 2-aminopyrimidine derivatives as potential JAK2 inhibitors. Materials & methods: Quantitative structure-activity relationship (QSAR) approaches (hologram QSAR and comparative molecular similarity indices analysis), molecular dynamics simulations, binding energy calculations and pharmacokinetic predictions were employed. Results: Reliable QSAR models, binding mode and binding interactions of JAK2 inhibitors were obtained and these obtained results were used as the key information for rational design of highly potent JAK2 inhibitors. Conclusion: The concept of new potential JAK2 inhibitors integrated from the obtained results was proved, producing two newly designed compounds, D01 and D02, with potential for use as JAK2 inhibitors.

Virtual Screening Identifies Novel and Potent Inhibitors of Mycobacterium tuberculosis PknB with Antibacterial Activity.

Mycobacterium tuberculosis protein kinase B (PknB) is essential to mycobacterial growth and has received considerable attention as an attractive target for novel anti-tuberculosis drug development. Here, virtual screening, validated by biological assays, was applied to select candidate inhibitors of M. tuberculosis PknB from the Specs compound library (www.specs.net). Fifteen compounds were identified as hits and selected for in vitro biological assays, of which three indoles (2, AE-848/42799159; 4, AH-262/34335013; 10, AP-124/40904362) inhibited growth of M. tuberculosis H37Rv with minimal inhibitory concentrations of 6.2, 12.5, and 6.2 µg/mL, respectively. Two compounds, 2 and 10, inhibited M. tuberculosis PknB activity in vitro, with IC50 values of 14.4 and 12.1 µM, respectively, suggesting this to be the likely basis of their anti-tubercular activity. In contrast, compound 4 displayed anti-tuberculosis activity against M. tuberculosis H37Rv but showed no inhibition of PknB activity (IC50 > 128 µM). We hypothesize that hydrolysis of its ethyl ester to a carboxylate moiety generates an active species that inhibits other M. tuberculosis enzymes. Molecular dynamics simulations of modeled complexes of compounds 2, 4, and 10 bound to M. tuberculosis PknB indicated that compound 4 has a lower affinity for M. tuberculosis PknB than compounds 2 and 10, as evidenced by higher calculated binding free energies, consistent with experiment. Compounds 2 and 10 therefore represent candidate inhibitors of M. tuberculosis PknB that provide attractive starting templates for optimization as anti-tubercular agents.

In silico design of novel quinazoline-based compounds as potential Mycobacterium tuberculosis PknB inhibitors through 2D and 3D-QSAR, molecular dynamics simulations combined with pharmacokinetic predictions.

Serine/threonine protein kinase B (PknB) is essential to Mycobacterium tuberculosis (M. tuberculosis) cell division and metabolism and a potential anti-tuberculosis drug target. Here we apply Hologram Quantitative Structure Activity Relationship (HQSAR) and three-dimensional QSAR (Comparative Molecular Similarity Indices Analysis (CoMSIA)) methods to investigate structural requirements for PknB inhibition by a series of previously described quinazoline derivatives. PknB binding of quinazolines was evaluated by molecular dynamics (MD) simulations of the catalytic domain and binding energies calculated by Molecular Mechanics/Poisson Boltzmann Surface Area (MM-PBSA) and Molecular Mechanics/Generalized Born Surface Area (MM-GBSA) methods. Evaluation of a training set against experimental data showed both HQSAR and CoMSIA models to reliably predict quinazoline binding to PknB, and identified the quinazoline core and overall hydrophobicity as the major contributors to affinity. Calculated binding energies also agreed with experiment, and MD simulations identified hydrogen bonds to Glu93 and Val95, and hydrophobic interactions with Gly18, Phe19, Gly20, Val25, Thr99 and Met155, as crucial to PknB binding. Based on these results, additional quinazolines were designed and evaluated in silico, with HQSAR and CoMSIA models identifying sixteen compounds, with predicted PknB binding superior to the template, whose activity spectra and physicochemical, pharmacokinetic, and anti-M. tuberculosis properties were assessed. Compound, D060, bearing additional ortho- and meta-methyl groups on its R2 substituent, was superior to template regarding PknB inhibition and % caseum fraction unbound, and equivalent in other aspects, although predictions identified hepatotoxicity as a likely issue with the quinazoline series. These data provide a structural basis for rational design of quinazoline derivatives with more potent PknB inhibitory activity as candidate anti-tuberculosis agents.

Discovery of novel and potent InhA inhibitors by an in silico screening and pharmacokinetic prediction.

Aim: In silico screening approaches were performed to discover novel InhA inhibitors. Methods: Candidate InhA inhibitors were obtained from the combination of virtual screening and pharmacokinetic prediction. In addition, molecular mechanics Poisson-Boltzmann surface area, molecular mechanics Generalized Born surface area and WaterSwap methods were performed to investigate the binding interactions and binding energy of candidate compounds. Results: Four candidate compounds with suitable physicochemical, pharmacokinetic and antibacterial properties are proposed. The crucial interactions of the candidate compounds were H-bond, pi-pi and sigma-pi interactions observed in the InhA binding site. The binding affinity of these compounds was improved by hydrophobic interactions with hydrophobic side chains in the InhA pocket. Conclusion: The four newly identified InhA inhibitors reported in this study could serve as promising hit compounds against Mycobacterium tuberculosis and may be considered for further experimental studies.

Identification of Potent DNA Gyrase Inhibitors Active against Mycobacterium tuberculosis.

Mycobacterium tuberculosis DNA gyrase manipulates the DNA topology using controlled breakage and religation of DNA driven by ATP hydrolysis. DNA gyrase has been validated as the enzyme target of fluoroquinolones (FQs), second-line antibiotics used for the treatment of multidrug-resistant tuberculosis. Mutations around the DNA gyrase DNA-binding site result in the emergence of FQ resistance in M. tuberculosis; inhibition of DNA gyrase ATPase activity is one strategy to overcome this. Here, virtual screening, subsequently validated by biological assays, was applied to select candidate inhibitors of the M. tuberculosis DNA gyrase ATPase activity from the Specs compound library (www.specs.net). Thirty compounds were identified and selected as hits for in vitro biological assays, of which two compounds, G24 and G26, inhibited the growth of M. tuberculosis H37Rv with a minimal inhibitory concentration of 12.5 µg/mL. The two compounds inhibited DNA gyrase ATPase activity with IC50 values of 2.69 and 2.46 µM, respectively, suggesting this to be the likely basis of their antitubercular activity. Models of complexes of compounds G24 and G26 bound to the M. tuberculosis DNA gyrase ATP-binding site, generated by molecular dynamics simulations followed by pharmacophore mapping analysis, showed hydrophobic interactions of inhibitor hydrophobic headgroups and electrostatic and hydrogen bond interactions of the polar tails, which are likely to be important for their inhibition. Decreasing compound lipophilicity by increasing the polarity of these tails then presents a likely route to improving the solubility and activity. Thus, compounds G24 and G26 provide attractive starting templates for the optimization of antitubercular agents that act by targeting DNA gyrase.

Binding interaction of protoberberine alkaloids against acetylcholinesterase (AChE) using molecular dynamics simulations and QM/MM calculations.

Acetylcholinesterase (AChE) plays a vital role in Alzheimer's disease (AD), which is one of the most common causes of dementia. Discovering new effective inhibitors against AChE activity is seen to be one of the effective approaches to reduce the suffering from AD. Protoberberine alkaloids isolated from natural resources have previously been reported as potent AChE inhibitors. In order to gain insights into how these alkaloids could inhibit AChE, berberine, palmatine, and cyclanoline were selected to investigate in terms of binding orientation and their key interactions with AChE using molecular docking and molecular dynamics simulations and quantum chemical calculations. The results revealed that the molecular dynamics structures of palmatine and berberine indicated that their equilibrated structures did not occupy the gorge but they slightly moved away from the catalytic site (CAS). For cyclanoline, the binding mode was quite different from those of donepezil and the other protoberberine alkaloids: it preferred to stay deeper in the CAS site. Interaction energies and residual interaction energies confirmed that the key interactions for palmatine and berberine were π-π interactions with Trp286 and Tyr341 and H-bond interactions with Tyr124. Cyclanoline formed π-π interactions with Trp86 and H-bonds to the amino acids in the CAS site. The results suggested the importance of aromaticity in the core structure and the flexibility of the core structure or the substituents in order to fit into the narrow gorge. The HOMO, LUMO, bioavailability, drug-likeness and pharmacokinetics were also predicted. The results obtained will be useful for further AD drug development.

Adsorption study of lac dyes with chitosan coated on silk fibroin using molecular dynamics simulations.

Silk is a protein polymer composed of the polypeptide chains including the repeating units of glycine and alanine. Lac dye is composed mainly of two major anthraquinone based components: laccaic acids A and B. Previously, chitosan was reported and used to coat silk in the lac dyeing process for enhancing the uptake of lac dye on silk. Therefore, this work aims to explain why chitosan can help in lac dyeing process on silk by using molecular docking and molecular dynamics (MD) simulations. The molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) analysis was also applied to calculate the binding free energy. The results revealed the attractive interaction between silk and chitosan. Moreover, an increasing unit of acetylglucosamine in the chitosan structure increases the binding interaction between silk and chitosan. After that, the binding between silk complexed with chitosan and laccaic acids A and B were reported. It was clearly found that the average of binding free energies between lac dyes and silk complexed with chitosan (-257.7 and -230.9 kJ/mol) was lower than those between lac dyes and silk without chitosan (-13.4 and -108.5 kJ/mol) indicating the better binding of lac dyes when chitosan is added on the silk surface. The obtained results can be explained why the existence of chitosan on silk surface could increase the binding of lac dyes. Therefore, this study can be used as a guideline in order to understand and improve the fastness properties of textiles.

Crystal structure of 5-[(benzo-yloxy)meth-yl]-5,6-dihy-droxy-4-oxo-cyclo-hex-2-en-1-yl benzoate.

The crystal structure of the natural product zeylenone, C21H18O7, was confirmed by single-crystal X-ray diffraction. The crystal structure has three chiral centers at positions C1, C5 and C6 of the cyclo-hexa-none ring, but the absolute configuration could not be determined reliably. The methyl benzoate and benzo-yloxy substituents at positions C1 and C5 of the cyclo-hexenone ring are on the same side of the ring with the dihedral angle between their mean planes being 16.25 (10)°. These rings are almost perpendicular to the cyclo-hexenone ring. The benzoate groups and two hydroxyl groups on the cyclo-hexenone ring form strong hydrogen bonds to consolidate the crystal structure. In addition, weak C-H⋯O hydrogen bonds also contribute to the packing of the structure.

Anticodon-binding domain swapping in a nondiscriminating aspartyl-tRNA synthetase reveals contributions to tRNA specificity and catalytic activity.

The nondiscriminating aspartyl-tRNA synthetase (ND-AspRS), found in many archaea and bacteria, covalently attaches aspartic acid to tRNAAsp and tRNAAsn generating a correctly charged Asp-tRNAAsp and an erroneous Asp-tRNAAsn . This relaxed tRNA specificity is governed by interactions between the tRNA and the enzyme. In an effort to assess the contributions of the anticodon-binding domain to tRNA specificity, we constructed two chimeric enzymes, Chimera-D and Chimera-N, by replacing the native anticodon-binding domain in the Helicobacter pylori ND-AspRS with that of a discriminating AspRS (Chimera-D) and an asparaginyl-tRNA synthetase (AsnRS, Chimera-N), both from Escherichia coli. Both chimeric enzymes showed similar secondary structure compared to wild-type (WT) ND-AspRS and maintained the ability to form dimeric complexes in solution. Although less catalytically active than WT, Chimera-D was more discriminating as it aspartylated tRNAAsp over tRNAAsn with a specificity ratio of 7.0 compared to 2.9 for the WT enzyme. In contrast, Chimera-N exhibited low catalytic activity toward tRNAAsp and was unable to aspartylate tRNAAsn . The observed catalytic activities for the two chimeras correlate with their heterologous toxicity when expressed in E. coli. Molecular dynamics simulations show a reduced hydrogen bond network at the interface between the anticodon-binding domain and the catalytic domain in Chimera-N compared to Chimera-D or WT, explaining its lower stability and catalytic activity.