Mechanics Poisson-Boltzmann Surface Area Calculations Research Articles

Molecular and energetic analysis of the interaction and specificity of Maximin 3 with lipid membranes: In vitro and in silico assessments.

In this study, the interaction of antimicrobial peptide Maximin 3 (Max3) with three different lipid bilayer models was investigated to gain insight into its mechanism of action and membrane specificity. Bilayer perturbation assays using liposome calcein leakage dose-response curves revealed that Max3 is a selective membrane-active peptide. Dynamic light scattering recordings suggest that the peptide incorporates into the liposomal structure without producing a detergent effect. Langmuir monolayer compression assays confirmed the membrane inserting capacity of the peptide. Attenuated total reflection-Fourier transform infrared spectroscopy showed that the fingerprint signals of lipid phospholipid hydrophilic head groups and hydrophobic acyl chains are altered due to Max3-membrane interaction. On the other hand, all-atom molecular dynamics simulations (MDS) of the initial interaction with the membrane surface corroborated peptide-membrane selectivity. Peptide transmembrane MDS shed light on how the peptide differentially modifies lipid bilayer properties. Molecular mechanics Poisson-Boltzmann surface area calculations revealed a specific electrostatic interaction fingerprint of the peptide for each membrane model with which they were tested. The data generated from the in silico approach could account for some of the differences observed experimentally in the activity and selectivity of Max3.

Biophysical and structural characterization of tetramethrin serum protein complex and its toxicological implications.

Tetramethrin (TMT) is a commonly used insecticide and has a carcinogenic and neurodegenerative effect on humans. The binding mechanism and toxicological implications of TMT to human serum albumin (HSA) were examined in this study employing a combination of biophysical and computational methods indicating moderate binding affinity and potential hepato and renal toxicity. Fluorescence quenching experiments showed that TMT binds to HSA with a moderate affinity, and the binding process was spontaneous and predominantly enthalpy-driven. Circular dichroism spectroscopy revealed that TMT binding did not induce any significant conformational changes in HSA, resulting in no changes in its alpha-helix content. The binding site and modalities of TMT interactions with HSA as computed by molecular docking and molecular dynamics simulations revealed that it binds to Sudlow site II of HSA via hydrophobic interactions through its dimethylcyclopropane carboxylate methyl propanyl group. The structural dynamics of TMT induce proper fit into the binding site creating increased and stabilizing interactions. Additionally, molecular mechanics-Poisson Boltzmann surface area calculations also indicated that non-polar and van der Waals were found to be the major contributors to the high binding free energy of the complex. Quantum mechanics (QM) revealed the conformational energies of the binding confirmation and the degree of deviation from the global minimum energy conformation of TMT. The results of this study provide a comprehensive understanding of the binding mechanism of TMT with HSA, which is important for evaluating the toxicity of this insecticide in humans.

Identification of PPA1 inhibitor candidates for potential repurposing in cancer medicine.

Inorganic pyrophosphatase 1 (PPA1) is pivotal to cellular metabolism as it facilitates the hydrolysis of PPi-a by-product of various metabolic processes that influence cell growth and differentiation. Overexpression of PPA1 enzyme has been linked to diminished patient survival and was shown to influence tumor cell dynamics, thereby positioning it as a potential therapy target for a variety of cancers including colorectal cancer, diffuse large B-cell lymphoma, and lung adenocarcinoma. Despite this therapeutic promise, there are no known inhibitors of PPA1 as of today. In this study, we searched for potential PPA1 inhibitors using a molecular docking screen of 30 470 compounds with a history of clinical trials and/or US Food and Drug Administration approval. We specifically targeted the active pocket that coincides with the established catalytic domain. Our screen identified promising hits, which we further subjected to ADMET (absorption, distribution, metabolism, excretion, and toxicity) filtering. Subsequent molecular dynamics (MD) analyses were conducted on devazepide, quinotolast, and tarazepide-the three substances that successfully navigated all filters. MD analyses reinforced the stability of the protein-ligand complexes and confirmed ligand binding, as substantiated by our root mean square deviation, radius of gyration and secondary structures of proteins analyses. Furthermore, Molecular Mechanics Poisson-Boltzmann Surface Area calculations post-MD identified devazepide and quinotolast as showing higher binding affinities; being supported by principal component analysis, free energy landscape, and dynamic cross-correlation matrix results. Overall, our study reveals devazepide and quinotolast as potential candidates for PPA1 inhibition which could be considered for repurposing studies that need further experimental validation. These results not only reveal a potential for clinical repurposing for PPA1 inhibition but they also offer valuable insights into the development of future compounds for targeting the crucial PPA1 enzyme.

Cheminformatics-Based Study Identifies Potential Ebola VP40 Inhibitors.

The Ebola virus (EBOV) is still highly infectious and causes severe hemorrhagic fevers in primates. However, there are no regulatorily approved drugs against the Ebola virus disease (EVD). The highly virulent and lethal nature of EVD highlights the need to develop therapeutic agents. Viral protein 40 kDa (VP40), the most abundantly expressed protein during infection, coordinates the assembly, budding, and release of viral particles into the host cell. It also regulates viral transcription and RNA replication. This study sought to identify small molecules that could potentially inhibit the VP40 protein by targeting the N-terminal domain using an in silico approach. The statistical quality of AutoDock Vina's capacity to discriminate between inhibitors and decoys was determined, and an area under the curve of the receiver operating characteristic (AUC-ROC) curve of 0.791 was obtained. A total of 29,519 natural-product-derived compounds from Chinese and African sources as well as 2738 approved drugs were successfully screened against VP40. Using a threshold of -8 kcal/mol, a total of 7, 11, 163, and 30 compounds from the AfroDb, Northern African Natural Products Database (NANPDB), traditional Chinese medicine (TCM), and approved drugs libraries, respectively, were obtained after molecular docking. A biological activity prediction of the lead compounds suggested their potential antiviral properties. In addition, random-forest- and support-vector-machine-based algorithms predicted the compounds to be anti-Ebola with IC50 values in the micromolar range (less than 25 μM). A total of 42 natural-product-derived compounds were identified as potential EBOV inhibitors with desirable ADMET profiles, comprising 1, 2, and 39 compounds from NANPDB (2-hydroxyseneganolide), AfroDb (ZINC000034518176 and ZINC000095485942), and TCM, respectively. A total of 23 approved drugs, including doramectin, glecaprevir, velpatasvir, ledipasvir, avermectin B1, nafarelin acetate, danoprevir, eltrombopag, lanatoside C, and glycyrrhizin, among others, were also predicted to have potential anti-EBOV activity and can be further explored so that they may be repurposed for EVD treatment. Molecular dynamics simulations coupled with molecular mechanics Poisson-Boltzmann surface area calculations corroborated the stability and good binding affinities of the complexes (-46.97 to -118.9 kJ/mol). The potential lead compounds may have the potential to be developed as anti-EBOV drugs after experimental testing.

Inhibiting Leishmania donovani Sterol Methyltransferase to Identify Lead Compounds Using Molecular Modelling.

The recent outlook of leishmaniasis as a global public health concern coupled with the reportage of resistance and lack of efficacy of most antileishmanial drugs calls for a concerted effort to find new leads. The study combined In silico and in vitro approaches to identify novel potential synthetic small-molecule inhibitors targeting the Leishmania donovani sterol methyltransferase (LdSMT). The LdSMT enzyme in the ergosterol biosynthetic pathway is required for the parasite's membrane fluidity, distribution of membrane proteins, and control of the cell cycle. The lack of LdSMT homologue in the human host and its conserved nature among all Leishmania parasites makes it a viable target for future antileishmanial drugs. Initially, six known inhibitors of LdSMT with IC50 < 10 μM were used to generate a pharmacophore model with a score of 0.9144 using LigandScout. The validated model was used to screen a synthetic library of 95,630 compounds obtained from InterBioScreen limited. Twenty compounds with pharmacophore fit scores above 50 were docked against the modelled three-dimensional structure of LdSMT using AutoDock Vina. Consequently, nine compounds with binding energies ranging from -7.5 to -8.7 kcal/mol were identified as potential hit molecules. Three compounds comprising STOCK6S-06707, STOCK6S-84928, and STOCK6S-65920 with respective binding energies of -8.7, -8.2, and -8.0 kcal/mol, lower than 22,26-azasterol (-7.6 kcal/mol), a known LdSMT inhibitor, were selected as plausible lead molecules. Molecular dynamics simulation studies and molecular mechanics Poisson-Boltzmann surface area calculations showed that the residues Asp25 and Trp208 were critical for ligand binding. The compounds were also predicted to have antileishmanial activity with reasonable pharmacological and toxicity profiles. When the antileishmanial activity of the three hits was evaluated in vitro against the promastigotes of L. donovani, mean half-maximal inhibitory concentrations (IC50) of 21.9 ± 1.5 μM (STOCK6S-06707), 23.5 ± 1.1 μM (STOCK6S-84928), and 118.3 ± 5.8 μM (STOCK6S-65920) were obtained. Furthermore, STOCK6S-84928 and STOCK6S-65920 inhibited the growth of Trypanosoma brucei, with IC50 of 14.3 ± 2.0 μM and 18.1 ± 1.4 μM, respectively. The identified compounds could be optimised to develop potent antileishmanial therapeutic agents.

Targeting Natural Plant Metabolites for Hunting SARS-CoV-2 Omicron BA.1 Variant Inhibitors: Extraction, Molecular Docking, Molecular Dynamics, and Physicochemical Properties Study.

(1) Background: SARS-CoV-2 Omicron BA.1 is the most common variation found in most countries and is responsible for 99% of cases in the United States. To overcome this challenge, there is an urgent need to discover effective inhibitors to prevent the emerging BA.1 variant. Natural products, particularly flavonoids, have had widespread success in reducing COVID-19 prevalence. (2) Methods: In the ongoing study, fifteen compounds were annotated from Echium angustifolium and peach (Prunus persica), which were computationally analyzed using various in silico techniques. Molecular docking calculations were performed for the identified phytochemicals to investigate their efficacy. Molecular dynamics (MD) simulations over 200 ns followed by molecular mechanics Poisson–Boltzmann surface area calculations (MM/PBSA) were performed to estimate the binding energy. Bioactivity was also calculated for the best components in terms of drug likeness and drug score. (3) Results: The data obtained from the molecular docking study demonstrated that five compounds exhibited remarkable potency, with docking scores greater than −9.0 kcal/mol. Among them, compounds 1, 2 and 4 showed higher stability within the active site of Omicron BA.1, with ΔGbinding values of −49.02, −48.07, and −67.47 KJ/mol, respectively. These findings imply that the discovered phytoconstituents are promising in the search for anti-Omicron BA.1 drugs and should be investigated in future in vitro and in vivo research.

Exploration of potential inhibitors for SARS-CoV-2 Mpro considering its mutants via structure-based drug design, molecular docking, MD simulations, MM/PBSA, and DFT calculations.

The main protease (Mpro) of SARS-COV-2 plays a vital role in the viral life cycle and pathogenicity. Due to its specific attributes, this 3-chymotrypsin like protease can be a reliable target for the drug design to combat COVID-19. Since the advent of COVID-19, Mpro has undergone many mutations. Here, the impact of 10 mutations based on their frequency and five more based on their proximity to the active site was investigated. For comparison purposes, the docking process was also performed against the Mpros of SARS-COV and MERS-COV. Four inhibitors with the highest docking score (11b, α-ketoamide 13b, Nelfinavir, and PF-07321332) were selected for the structure-based ligand design via fragment replacement, and around 2000 new compounds were thus obtained. After the screening of these new compounds, the pharmacokinetic properties of the best ones were predicted. In the last step, comparative molecular dynamics (MD) simulations, molecular mechanics Poisson-Boltzmann surface area calculations (MM/PBSA), and density functional theory calculations were performed. Among the 2000 newly designed compounds, three of them (NE1, NE2, and NE3), which were obtained by modifications of Nelfinavir, showed the highest affinity against all the Mpro targets. Together, NE1 compound is the best candidate for follow-up Mpro inhibition and drug development studies.

Conducting the RBD of SARS-CoV-2 Omicron Variant with Phytoconstituents from Euphorbia dendroides to Repudiate the Binding of Spike Glycoprotein Using Computational Molecular Search and Simulation Approach.

(1) Background: Natural constituents are still a preferred route for counteracting the outbreak of COVID-19. Essentially, flavonoids have been found to be among the most promising molecules identified as coronavirus inhibitors. Recently, a new SARS-CoV-2 B.1.1.529 variant has spread in many countries, which has raised awareness of the role of natural constituents in attempts to contribute to therapeutic protocols. (2) Methods: Using various chromatographic techniques, triterpenes (1–7), phenolics (8–11), and flavonoids (12–17) were isolated from Euphorbia dendroides and computationally screened against the receptor-binding domain (RBD) of the SARS-CoV-2 Omicron variant. As a first step, molecular docking calculations were performed for all investigated compounds. Promising compounds were subjected to molecular dynamics simulations (MD) for 200 ns, in addition to molecular mechanics Poisson–Boltzmann surface area calculations (MM/PBSA) to determine binding energy. (3) Results: MM/PBSA binding energy calculations showed that compound 14 (quercetin-3-O-β-D-glucuronopyranoside) and compound 15 (quercetin-3-O-glucuronide 6″-O-methyl ester) exhibited strong inhibition of Omicron, with ΔGbinding of −41.0 and −32.4 kcal/mol, respectively. Finally, drug likeness evaluations based on Lipinski’s rule of five also showed that the discovered compounds exhibited good oral bioavailability. (4) Conclusions: It is foreseeable that these results provide a novel intellectual contribution in light of the decreasing prevalence of SARS-CoV-2 B.1.1.529 and could be a good addition to the therapeutic protocol.

Molecular docking and molecular dynamics simulation of Bacillus thuringiensis dehalogenase against haloacids, haloacetates and chlorpyrifos

The high dependency and surplus use of agrochemical products have liberated enormous quantities of toxic halogenated pollutants into the environment and threaten the well-being of humankind. Herein, this study performed molecular docking, molecular dynamic (MD) simulations, molecular mechanics-Poisson Boltzmann Surface Area (MM-PBSA) calculations on the DehH2 from Bacillus thuringiensis, to identify the order of which the enzyme degrades different substrates, haloacids, haloacetate and chlorpyrifos. The study discovered that the DehH2 favored the degradation of haloacids and haloacetates (−3.3 − 4.6 kcal/mol) and formed three hydrogen bonds with Asp125, Arg201 and Lys202. Despite the inconclusive molecular docking result, chlorpyrifos was consistently shown to be the least favored substrate of the DehH2 in MD simulations and MM-PBSA calculations. Results of MD simulations revealed the DehH2-haloacid- (RMSD 0.15 − 0.25 nm) and DehH2-haloacetates (RMSF 0.05 − 0.25 nm) were more stable, with the DehH2-L-2CP complex being the most stable while the least was the DehH2-chlorpyrifos (RMSD 0.295 nm; RMSF 0.05 − 0.59 nm). The Molecular Mechanics Poisson-Boltzmann Surface Area calculations showed the DehH2-L-2CP complex (−24.27 kcal/mol) having the lowest binding energy followed by DehH2-MCA (−22.78 kcal/mol), DehH2-D-2CP (−21.82 kcal/mol), DehH2-3CP (−21.11 kcal/mol), DehH2-2,2-DCP (−18.34 kcal/mol), DehH2-2,3-DCP (−8.34 kcal/mol), DehH2-TCA (−7.62 kcal/mol), while chlorpyrifos was unable to spontaneously bind to DehH2 (+127.16 kcal/mol). In a nutshell, the findings of this study offer valuable insights into the rational tailoring of the DehH2 for expanding its substrate specificity and catalytic activity in the near future. Communicated by Ramaswamy H. Sarma

Identification of novel and selective agonists for ABA receptor PYL3

Abscisic acid (ABA) although complicated and expensive to produce, plays an important role in signalling responsible for regulation of developmental manifestations such as seed maturation and surviving through stress conditions. Hence, development of cost effective molecules with minimal side effects that mimic the functions of ABA is the need of the hour. In this agreement, we screened a series of 27 in-house synthesized 3-methyleneisoindolin-1-one molecules over three ABA receptors (PYR1, PYL1, and PYL3). The commercial ABA agonist Pyrabactin was taken as a standard ligand in this study. The top three molecules for each receptor were selected and further evaluated to estimate the dynamical contribution and complex stability via Molecular Mechanics-Poisson Boltzmann surface area calculations. Two molecules (Mol26 and Mol25) showed higher binding free energy and stable complex conformation for PYL3 in comparison to Pyrabactin. This study revealed the structural basis of the binding mechanism of 3-methyleneisoindolin-1-one molecules with ABA receptors. Mol26 and Mol25 were identified for the development of specific PYL3 agonists with a vast potential in agriculture to accentuate the ABA like action in plants.

Computational Study of Encapsulation of Polyaromatic Hydrocarbons by Endo-Functionalized Receptors in Nonpolar Medium.

Polycyclic aromatic hydrocarbons (PAHs) constitute a large group of organic pollutants produced from either natural or artificial sources during the incomplete combustion of fossil fuels or derived from various industrial processes (such as refinery processes of crude petroleum). They are seriously hazardous to human health, and removing them is of major importance. The complexation likeliness with and selective recognition of PAH guests by endo-functionalized molecular tube hosts (host-abu and host-abtu) in a nonpolar medium are investigated using classical molecular dynamics simulation and quantum calculation to probe the factors and the molecular mechanism involved in complexation processes. We examine the role of different guest molecules in the structural changes of hosts, a prelude to van der Waals interactions and binding free energy in the complexation process. These types of host-guest interactions depend on various factors. We find that (i) both the host molecules (host-abtu and host-abu) interact with the guest π-electron cloud almost equally and (ii) these interactions also depend on the molecular size of PAHs. The larger the nonpolar surface area of PAHs, the greater the interactions with the host, and the more extensive the π-electron cloud of the guest, the stronger the interactions. The linear PAHs interact more strongly than isomeric branched/curved PAHs, and the presence of heteroatoms on PAHs decreases the interactions with the host by creating repulsion between the lone pairs of heteroatoms and the π-electron cloud of the host. Noncovalent van der Waals interactions and N-H···π interactions dominate the high affinities of PAHs toward host-abu and host-abtu. The potential of mean force and molecular mechanics Poisson-Boltzmann surface area calculations reveal that all host-guest complexes are energetically stable.

Modeling antimalarial and antihuman African trypanosomiasis compounds: a ligand- and structure-based approaches.

This study examines the interaction of 137 antimalarial and antihuman African trypanosomiasis compounds [bis(2-aminoimidazolines), bisguanidinediphenyls and polyamines] on three different in vitro assays (Trypanosoma brucei rhodesiense (T.b.r.), Plasmodium falciparum (P.f.) and cytotoxicity-L6 cells). ΔTm values, wherever available, were also examined for the considered ligands. Eight DNA-ligand complexes and one DNA structure without ligand were selected from protein data bank (PDB) based on the structural similarity. Geometry optimization of all the considered ligands was carried out at the B3LYP/6-31G(d) level of theory. The AutoDock4 tool was utilized for the docking of these molecules at the minor groove of nine selected DNA crystal structures. We observed DT20, DA6, DT8 and DT19 residues generally interact with most of the considered ligands. Molecular dynamics simulations, molecular mechanics-generalized born surface area and molecular mechanics-Poisson Boltzmann surface area calculations indicate that the docked poses are generally stable and docked ligands do not show much deviation in the minor groove of DNA until 10ns simulation. Efficient and statistically significant quantitative structure-activity relationship models for T.b.r., P.f., C-L6 and ΔTm values were developed. All the generated models are internally and externally validated. We predicted a few ligands with significant IC50 values against P.f. based on the developed models. These results may help to design new and potent antimalarial and antihuman African trypanosomal compounds.

Underlying mechanistic insights into the structural properties of melamine and uric acid complexes with compositional variation under ambient conditions

The structural properties of melamine-uric acid complexes (which are responsible for kidney stones) with compositional variations are examined using a series of classical molecular dynamics simulations. The preferential interaction parameters imply that melamine interacts more strongly with uric acid than with other melamine molecules present in the system, whereas uric acid preferentially interacts with other uric acid molecules rather than with melamine. The stronger interactions among uric acid molecules produce higher-order uric acid clusters, which “drag” neighboring melamine molecules to be added to a cluster. Determination of orientational preferences between aromatic planes reveals that π–π stacking is responsible for uric acid self-association but less significant for melamine-melamine and melamine-uric acid accumulation. Cluster structure analyses suggest that higher concentrations of melamine, uric acid, or both result in a large insoluble melamine-uric acid complex cluster. Molecular mechanics-Poisson Boltzmann surface area calculations give a negative binding energy, indicating favorable complexation between melamine and uric acid molecules. Moreover, the overall complexation energy [ΔG0(mel-mel)+ ΔG0(uri-uri)+ ΔG0(mel-uri)] is more negative than ΔG0bind(mel-uri). The lifetime of melamine dimers is quite low compared with those of uric acid-uric acid and melamine-uric acid dimers, resulting in a low percentage of larger clusters for melamine-melamine interaction and a significant percentage of higher-order melamine-uric acid and uric acid-uric acid clusters with longer lifetimes. Furthermore, melamine and uric acid form strong hydrogen bonds, and melamine-melamine interactions are dominated by hydrogen bonding, whereas uric acid forms only a small number of hydrogen bonds with other uric acid molecules.

Theoretical analyses on enantiospecificity of L-2-haloacid dehalogenase (DehL) from Rhizobium sp. RC1 towards 2-chloropropionic acid

Dehalogenases continue to garner interest of the scientific community due to their potential applications in bioremediation of halogen-contaminated environment and in synthesis of various industrially relevant products. Example of such enzymes is DehL, an L-2-haloacid dehalogenase (EC 3.8.1.2) from Rhizobium sp. RC1 that catalyses the specific cleavage of halide ion from L-2-halocarboxylic acids to produce the corresponding D-2-hydroxycarboxylic acids. Recently, the catalytic residues of DehL have been identified and its catalytic mechanism has been fully elucidated. However, the enantiospecificity determinants of the enzyme remain unclear. This information alongside a well-defined catalytic mechanism are required for rational engineering of DehL for substrate enantiospecificity. Therefore, using quantum mechanics/molecular mechanics and molecular mechanics Poisson-Boltzmann surface area calculations, the current study theoretically investigated the molecular basis of DehL enantiospecificity. The study found that R51L mutation cancelled out the dehalogenation activity of DehL towards it natural substrate, L-2-chloropropionate. The M48R mutation, however introduced a new activity towards D-2-chloropropionate, conveying the possibility of inverting the enantiospecificity of DehL from L-to d-enantiomer with a minimum of two simultaneous mutations. The findings presented here will play important role in the rational design of DehL dehalogenase for improving substrate utility.

Natural Product Neopeltolide as a Cytochrome bc1 Complex Inhibitor: Mechanism of Action and Structural Modification.

The marine natural product neopeltolide was isolated from a deep-water sponge specimen of the family Neopeltidae. Neopeltolide has been proven to be a new type of inhibitor of the cytochrome bc1 complex in the mitochondrial respiration chain. However, its detailed inhibition mechanism has remained unknown. In addition, neopeltolide is difficult to synthesize because of its very complex chemical structure. In the present work, the binding mode of neopeltolide was determined for the first time by integrating molecular docking, molecular dynamics simulations, and molecular mechanics Poisson-Boltzmann surface area calculations, which showed that neopeltolide is a Qo site inhibitor of the bc1 complex. Then, according to guidance via inhibitor-protein interaction analysis, structural modification was carried out with the aim to simplify the chemical structure of neopeltolide, leading to the synthesis of a series of new neopeltolide derivatives with much simpler chemical structures. The calculated binding energies (Δ Gcal) of the newly synthesized analogues correlated very well ( R2 = 0.90) with their experimental binding free energies (Δ Gexp), which confirmed that the computational protocol was reliable. Compound 45, bearing a diphenyl ether fragment, was successfully designed and synthesized as the most potent candidate (IC50 = 12 nM) against porcine succinate cytochrome c reductase. The molecular modeling results indicate that compound 45 formed a π-π interaction with Phe274 and two hydrogen bonds with Glu271 and His161. The present work provides a new starting point for future fungicide discovery to overcome the resistance that the existing bc1 complex inhibitors are facing.

Molecular modeling studies on the interactions of 7-methoxytacrine-4-pyridinealdoxime, 4-PA, 2-PAM, and obidoxime with VX-inhibited human acetylcholinesterase: a near attack conformation approach

7-methoxytacrine-4-pyridinealdoxime (7-MEOTA-4-PA, named hybrid 5C) is a compound formerly synthesized and evaluated in vitro, together with 4-pyridine aldoxime (4-PA) and commercial reactivators of acetylcholinesterase (AChE). This compound was designed with the purpose of being a prophylactic reactivator, capable of interacting with different subdomains of the active site of AChE. To investigate these interactions, theoretical results from docking were first compared with experimental data of hybrid 5C, 4-PA, and two commercial oximes, on the reactivation of human AChE (HssAChE) inhibited by VX. Then, further docking studies, molecular dynamics simulations, and molecular mechanics Poisson–Boltzmann surface area calculations, were carried out to investigate reactivation performances, considering the near attack conformation (NAC) approach, prior to the nucleophilic substitution mechanism. Our results helped to elucidate the interactions of such molecules with the different subdomains of the active site of HssAChE. Additionally, NAC poses of each oxime were suggested for further theoretical studies on the reactivation reaction.

Insights into the antibiotic resistance and inhibition mechanism of aminoglycoside phosphotransferase from Bacillus cereus: In silico and in vitro perspective.

Because of the lack of structural studies on aminoglycoside phosphotransferase (APH) from prevalent volatile human pathogen Bacillus cereus, aminoglycoside resistance therapeutics research remains elusive. Hence, in this computational study, we have performed homology modeling, molecular docking, molecular dynamics (MD), and principal component analysis studies on APH from B. cereus. The structure of APH was predicted by homology modeling using MODELLER 9v12 and validated for its stereochemical qualities. Sequence analysis study of the template (Protein Data Bank ID: 3TDW) and APH from B. cereus sensu lato group showed exact matching of active-site residues. The mechanism of substrate and inhibitor binding to APH was studied using molecular docking, which identified GTP as the more preferred substrate, whereas ZINC71575479 as the most effective inhibitor. The active-site residues, ARG41, TYR90, ASP195, and ASP215 at nucleotide triphosphate-binding cavity of APH were found to be involved in binding with substrate and inhibitor. Molecular dynamics simulation study of APH in apo form and bound form confirmed the stability and effective binding of GTP and ZINC71575479 in a dynamic state. Molecular mechanics Poisson-Boltzmann surface area calculations revealed energetic contributions of active-site residues of APH in binding with GTP and ZINC71575479. The principal component analysis revealed the internal global motion of APH in apo and complex form. Furthermore, experimental studies on APH from B. cereus ATCC 10876 validated the in silico findings for its inhibition. Thus, this study provides more information on structure-function relationships of APH from B. cereus and open avenues for designing effective strategies to overcome antibiotic resistance.

Systems Pharmacology Dissection of Multiscale Mechanisms of Action for Herbal Medicines in Treating Rheumatoid Arthritis.

As a chronic inflammatory and angiogenic disease with increased morbidity and mortality, rheumatoid arthritis (RA) is characterized by the proliferation of synovial tissue and the accumulation of excessive mononuclear infiltration, which always results in the joint deformity, disability, and eventually the destruction of the bone and cartilage. Traditional Chinese Medicine (TCM), with rich history of proper effectiveness in treating the inflammatory joint disease containing RA, has long combated such illness from, actually, an integrative and holistic point of view. However, its "multi-components" and "multi-targets" features make it very difficult to decipher the molecular mechanisms of RA from a systematic perspective if employing only routine methods. Presently, an innovative systems-pharmacology approach was introduced, which combined the ADME screening model, drug targeting, and network pharmacology, to explore the action mechanisms of botanic herbs for the treatment of RA. As a result, we uncovered 117 active compounds and 85 key molecular targets from seven RA-related herbs, which are mainly implicated in four signaling pathways, that is, vascular endothelial growth factor, PI3K-Akt, Toll-like receptor, and T-cell-receptor pathways. Additionally, the network relationships among the active components, target proteins, and pathways were further built to uncover the pharmacological characters of these herbs. Besides, molecular dynamics (MD) simulations and molecular mechanics-Poisson-Boltzmann surface area calculations were carried out to explore the binding interactions between the compounds and their receptors as well as to investigate the binding affinity of the ligand to their protein targets. In vitro experiments by ligand binding assays validate the reliability of the drug-target interactions as well as the MD results. The high binding affinities and good inhibitions of the active compounds indicate that the potential therapeutic effects of these herbal medicines for treating RA are exerted probably through the modulation of these relevant proteins, which further validates the rationality and reliability of the drug-target interactions as well as our the network-based analytical methods. This work may be of help for not only understanding the action mechanisms of TCM and for discovering new drugs from plants for the treatment of RA, but also providing a novel potential method for modern medicine in treating complex diseases.

Deciphering the catalytic amino acid residues of l-2-haloacid dehalogenase (DehL) from Rhizobium sp. RC1: An in silico analysis

The l-2-haloacid dehalogenases (EC 3.8.1.2) specifically cleave carbon-halogen bonds in the L-isomers of halogenated organic acids. These enzymes have potential applications for the bioremediation and synthesis of various industrial products. One such enzyme is DehL, the l-2-haloacid dehalogenase from Rhizobium sp. RC1, which converts the L-isomers of 2-halocarboxylic acids into the corresponding D-hydroxycarboxylic acids. However, its catalytic mechanism has not been delineated, and to enhance its efficiency and utility for environmental and industrial applications, knowledge of its catalytic mechanism, which includes identification of its catalytic residues, is required. Using ab initio fragment molecular orbital calculations, molecular mechanics Poisson-Boltzmann surface area calculations, and classical molecular dynamic simulation of a three-dimensional model of DehL-l-2-chloropropionic acid complex, we predicted the catalytic residues of DehL and propose its catalytic mechanism. We found that when Asp13, Thr17, Met48, Arg51, and His184 were individually replaced with an alanine in silico, a significant decrease in the free energy of binding for the DehL-l-2-chloropropionic acid model complex was seen, indicating the involvement of these residues in catalysis and/or structural integrity of the active site. Furthermore, strong inter-fragment interaction energies calculated for Asp13 and L-2-chloropropionic acid, and for a water molecule and His184, and maintenance of the distances between atoms in the aforementioned pairs during the molecular dynamics run suggest that Asp13 acts as the nucleophile and His184 activates the water involved in DehL catalysis. The results of this study should be important for the rational design of a DehL mutant with improved catalytic efficiency.

Naphthalenediimide-Linked Bisbenzimidazole Derivatives as Telomeric G-Quadruplex-Stabilizing Ligands with Improved Anticancer Activity.

Human telomeric G-quadruplex DNA stabilization has emerged as an exciting novel approach for anticancer drug development. In the present study, we have designed and synthesized three C2-symmetric bisubstituted bisbenzimidazole naphthalenediimide (NDI) ligands, ALI-C3, BBZ-ARO, and BBZ-AROCH2, which stabilize human telomeric G-quadruplex DNA with high affinity. Herein, we have studied the binding affinities and thermodynamic contributions of each of these molecules with G-quadruplex DNA and compared the same to those of the parent NDI analogue, BMSG-SH-3. Results of fluorescence resonance energy transfer and surface plasmon resonance demonstrate that these ligands have a higher affinity for G4-DNA over duplex DNA and induce the formation of a G-quadruplex. The binding equilibrium constants obtained from the microcalorimetry studies of BBZ-ARO, ALI-C3, and BBZ-AROCH2 were 8.47, 6.35, and 3.41 μM, respectively, with h-telo 22-mer quadruplex. These showed 10 and 100 times lower binding affinity with h-telo 12-mer and duplex DNA quadruplexes, respectively. Analysis of the thermodynamic parameters obtained from the microcalorimetry study suggests that interactions were most favorable for BBZ-ARO among all of the synthesized compounds. The ΔGfree obtained from molecular mechanics Poisson–Boltzmann surface area calculations of molecular dynamics (MD) simulation studies suggest that BBZ-ARO interacted strongly with G4-DNA. MD simulation results showed the highest hydrogen bond occupancy and van der Waals interactions were between the side chains of BBZ-ARO and the DNA grooves. A significant inhibition of telomerase activity (IC50 = 4.56 μM) and induced apoptosis in cancer cell lines by BBZ-ARO suggest that this molecule has the potential to be developed as an anticancer agent.