Binding Free Energy Estimation Research Articles

Inhibition Mechanism of Antimalarial Drugs Targeting the Cytochrome bc1 Complex

Plasmodium falciparum (P. falciparum) is the main parasite known to cause malaria in humans. The antimalarial drug atovaquone is known to inhibit the Qo-site of the cytochrome bc1 complex of P. falciparum, which ultimately blocks ATP synthesis, leading to cell death. Through the years, mutations of the P. falciparum cytochrome bc1 complex, causing resistance to atovaquone, have emerged. The present investigation applies molecular dynamics (MD) simulations to study how the specific mutations Y279S and L282V, known to cause atovaquone resistance in malarial parasites, affect the inhibition mechanism of two known inhibitors. Binding free energy estimates were obtained through free energy perturbation calculations but were unable to confidently resolve the effects of mutations due to the great complexity of the binding environment. Meanwhile, basic mechanistic considerations from the MD simulations provide a detailed characterization of inhibitor binding modes and indicate that the Y279S mutation weakens the natural binding of the inhibitors, while no conclusive effect of the L282V mutation could be observed.

Interactions mechanism of commonly used drugs for the treatment of Covid-19

In this study conformation analysis of seven drugs commonly used in the treatment of COVID-19 was performed. The most stable conformers of the drug molecules were used as initial data for docking analysis. Using the Cavityplus program, the probable most active binding sites of both apo and holo forms of COVID-19 main protease enzyme (Mpro) and spike glycoprotein of SARSCoV-2 receptors were determined. The interaction mechanisms of the 7 FDA approved drugs (arbidol, colchicine, dexamethasone, favipiravir, galidesivir, hydroxychloroquine, remdesivir) were examined using the AutoDock Vina program. The six of the seven drugs were found to be more stable in binding to apo form of COVID-19 Mpro and spike glycoprotein. Moreover, a set of molecular mechanics (MM) Poisson-Boltzmann (PB) surface area (SA) calculations on the investigated drugs-protein systems were performed and the estimated binding free energy of remdesivir and the apo form of Mpro system was found to be the best. The interaction results of FDA drugs with the apo form of COVID-19 Mpro and spike glycoprotein can play an important role for the treatment of COVID-19.
 
 KEY WORDS: COVID-19, Drugs, Molecular modelling, Conformational analysis, Molecular docking
 
 Bull. Chem. Soc. Ethiop. 2020, 34(3), 613-623.
 DOI: https://dx.doi.org/10.4314/bcse.v34i3.16

Inhibitory Potential of Phytochemicals on Interleukin-6-Mediated T-Cell Reduction in COVID-19 Patients: A Computational Approach.

Background:A recent COVID-19 pandemic has resulted in a large death toll rate globally and even no cure or vaccine has been successfully employed to combat this disease. Patients have been reported with multi-organ dysfunction along with acute respiratory distress syndrome which implies a critical situation for patients and made them difficult to breathe and survive. Moreover, pathology of COVID-19 is also related to cytokine storm which indicates the elevated levels of interleukin (IL)-1, IL-6, IL-12, and IL-18 along with tumor necrosis factor (TNF)-α. Among them, the proinflammatory cytokine IL-6 has been reported to be induced via binding of severe acute respiratory syndrome coronavirus 2 (SARS)-CoV-2 to the host receptors.Methodology:Interleukin-6 blockade has been proposed to constitute novel therapeutics against COVID-19. Thus, in this study, 15 phytocompounds with known antiviral activity have been subjected to test for their inhibitory effect on IL-6. Based on the affinity prediction, top 3 compounds (isoorientin, lupeol, and andrographolide) with best scores were selected for 50 ns molecular dynamics simulation and MMGB/PBSA binding free energy analysis.Results:Three phytocompounds including isoorientin, lupeol, and andrographolide have shown strong interactions with the targeted protein IL-6 with least binding energies (−7.1 to −7.7 kcal/mol). Drug-likeness and ADMET profiles of prioritized phytocompounds are also very prominsing and can be further tested to be potential IL-6 blockers and thus benficial for COVID-19 treatment. The moelcular dynamics simulation couple with MMGB/PBSA binding free energy estimation validated conformational stability of the ligands and stronger intermolecular binding. The mean RMSD of the complexes is as: IL6-isoorientin complex (3.97 Å ± 0.77), IL6-lupeol (3.97 Å ± 0.76), and IL6-andrographolide complex (3.96 Å ± 0.77). In addition, the stability observation was affirmed by compounds mean RMSD: isoorientin (0.72 Å ± 0.32), lupeol (mean 0.38 Å ± 0.08), and andrographolide (1.09 Å ± 0.49). A similar strong agreement on systems stability was unraveled by MMGB/PBSA that found net binding net ~ −20 kcal/mol for the complexes dominated by van der Waal interaction energy.Conclusion:It has been predicted that proposing potential IL-6 inhibitors with less side effects can help critical COVID-19 patients because it may control the cytokine storm, a major responsible factor of its pathogenesis. In this study, 3 potential phytocompounds have been proposed to have inhibitory effect on IL-6 that can be tested as potential therapeutic options against SARS-CoV-2.

Accurate Estimation of Protein-ligand Binding Free Energies Based on Geometric Restraints

Accurate Estimation of Protein-ligand Binding Free Energies Based on Geometric Restraints

Neuroprotective activity of Ulmus pumila L. in Alzheimer's disease in rats; role of neurotrophic factors

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative disorders which affects the hippocampus and cortical neurons leading to impairment of cognitive ability. Treatment of AD depends mainly on acetylcholinesterase inhibitors, however, a novel therapeutic approach is introduced based on the maintenance of neuronal viability and functionality exerted through neurotrophic factors. In the current study, Ulmus pumila L. leaves alcoholic extract was investigated for its neuroprotective activity in AlCl3-induced AD in rats. Rats were orally treated with AlCl3 (17 mg/kg) for 4 weeks followed by U. pumila extract (150 mg/kg b.wt.) for another 6 weeks. Treatment of neuro-intoxicated rats with U. pumila extract resulted in a significant regulation in neurotrophic factors; brain derived neurotrophic factor and transforming growth factor-β and pro-inflammatory cytokine; TNF. It also induced an elevation in serum levels of monoamine neurotransmitters; norepinephrine, dopamine and serotonin and a decline in brain acetlycholinesterase activity. U. pumila extract also showed potent antioxidant activity as indicated by the declined malondialdehyde and elevated reduced glutathione, catalase and super oxide dismutase levels in AD rats‘ brains. Histological improvement was detected in the cerebral cortex, the hippocampus and striatum of the treated rats. The phytochemical analysis of U. pumila extract revealed high contents of flavonoids and phenolics and the major compounds were isolated and chemically characterized. Additionally, U. pumila extract and the isolated compounds exerted a prominent activity in in-vitro acetylcholinesterase inhibition assay with kaempferol-3-O-β-glucoside being the most potent compound showing IC50 of 29.03 ± 0.0155 μM. A molecular docking study indicated high affinity of kaempferol-3-O-β-robinobioside on acetylcholine esterase binding site with estimated binding free energy of –8.26 kcal/mol.

Interaction Mechanism of the Germination Stimulants Karrikins and Their Receptor ShKAI2iB.

The significance of karrikins (KARs) in plant physiology opens a door for their application in the agricultural production. As the first event of the whole signaling pathway, the binding of smoke-derived signal molecules KARs to the receptor protein KAI2 triggers the germination of the primary dormant seeds of all angiosperms, not just the "fire-prone" taxa. In the present study, all-atom molecular dynamics simulations, along with the accurate estimation of the ligand-receptor binding free energy, were used to investigate the atomic level interaction of all the members of the KARs family (from KAR1 to KAR6) with the receptor ShKAI2iB, an intermediate-evolving KAI2 from Striga hermonthica. The calculated binding energy value of KAR1 to ShKAI2iB, -5.64 kcal/mol, is in good agreement with the available experimental data, -5.67 kcal/mol. The further analysis of the detailed interaction between each KAR and the protein reveals the primary reasons for the difference of the affinity of the diverse ligands with the receptor and displays the regional characteristics of the protein's active site. Our research will not only provide clues for the study of equivalent endogenous phytohormone, but also contribute to the development of synthetic germinating chemicals.

Alkaloids of Phaedranassa dubia (Kunth) J.F. Macbr. and Phaedranassa brevifolia Meerow (Amaryllidaceae) from Ecuador and its cholinesterase-inhibitory activity

Alzheimer's disease is considered the most common cause of dementia and, in an increasingly aging population worldwide, the quest for treatment is a priority. Amaryllidaceae alkaloids are of main interest because of their cholinesterase inhibition potential, which is the main palliative treatment available for this disease. We evaluated the alkaloidal profile and the in vitro inhibitory activity on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) of bulb alkaloid extract of Phaedranassa dubia and Phaedranassa brevifolia collected in Ecuador. Using gas chromatography coupled to mass spectrometry (GC-MS), we identified typical Amaryllidaceae alkaloids in these species, highlighting the presence of lycorine-type alkaloids in P. dubia and haemanthamine/crinine-type in P. brevifolia. The species P. dubia and P. brevifolia showed inhibitory activities against AChE (IC50 values of 25.48 ± 0.39 and 3.45 ± 0.29 μg.mL−1, respectively) and BuChE (IC50 values of 114.96 ± 4.94 and 58.89 ± 0.55 μg.mL−1, respectively). Computational experiments allowed us to understand the interactions of the alkaloids identified in these samples toward the active sites of AChE and BuChE. In silico, some alkaloids detected in these Amaryllidaceae species presented higher estimated binding free energy toward BuChE than galanthamine. This is the first study about the alkaloid profile and biological potential of P. brevifolia species.

Repurposing simeprevir, calpain inhibitor IV and a cathepsin F inhibitor against SARS-CoV-2 and insights into their interactions with Mpro

The world has come to a sudden halt due to the incessant spread of a viral pneumonia dubbed COVID-19 caused by the beta-coronavirus, SARS-CoV-2. The main protease of SARS-CoV-2 plays a key role in the replication and propagation of the virus in the host cells. Inhibiting the protease blocks the replication of the virus; therefore it is considered as an attractive therapeutic target. Here we describe the screening of the DrugBank database, a public repository for small molecule therapeutics, to identify approved or experimental phase drugs that can be repurposed against the main protease of SARS-CoV-2. The initial screening was performed on more than 13,000 drug entries in the target database using an energy optimised pharmacophore hypothesis AARRR. A sub-set of the molecules selected based on the fitness score was further screened using molecular docking by sequentially filtering the molecules through the high throughput virtual screening, extra precision and standard precision docking modalities. The best hits were subjected to binding free energy estimation using the MM-GBSA method. Approved drugs viz, Cobicistat, Larotrectinib and Simeprevir were identified as potential candidates for repurposing. Drugs in the discovery phase identified as inhibitors include the known cysteine protease inhibitors, Calpain inhibitor IV and an experimental cathepsin F inhibitor. In order to analyse the stability of the binding interactions, the known cysteine protease inhibitors viz, Simeprevir, calpain inhibitor IV and the cathepsin F inhibitor in complex Mpro were subjected to molecular dynamics simulations at 100 ns. Based on the results Simeprevir was found to be a strong inhibitor of SARS-CoV-2 Mpro. Communicated by Ramaswamy H. Sarma

Impact of HEC72702 chirality on the selective inhibition of hepatitis B virus capsid dimer: A dynamics-structure-energetics perspective.

Chirality in drug design has been attracting wide interests and attention over the years based on its innate potentials of enhancing the selectivity and prowess of therapeutic molecules. This approach was fundamental to the recent design of two inhibitors, where (R,R)-HEC72702 exhibited higher potency inhibition against hepatitis B virus capsid (HBVC) than (R,S)-HEC72702. Nevertheless, the detailed molecular mechanism has remained unresolved. Here, we apply multiple computational approaches to explore, validate, and differentiate the binding modes of (R,R) and (R,S)-HEC72702 and to explain the systematic roles mediated by chirality on the distinctive inhibition of HBVC dimer (HBVCd). Our findings revealed that chirality change from R,S to R,R engenders variations in the position of the propanoic acid group of HEC72702 toward the α5' and C-TER' region of HBVCd chain B which could explain the higher inhibitory affinity of (R,R)-HEC72702. Estimated binding free energies revealed a good correlation with bioactivity data. Moreover, analysis of energy decomposition revealed the prominent effects of van der Waals interactions in the binding process of both compounds to HBVCd. Furthermore, hierarchical clustering of residue-based energetic contributions suggested two hot-spot residues W125´ and F156´ play crucial roles in the systematic motions of the propanoic acid group toward chain B.

Multi-epitope based vaccine design against Sarcoptes scabiei paramyosin using immunoinformatics approach

Scabies is a parasitic skin infestation caused by mite Sarcoptes scabiei and is listed as one of the top 50 epidemic diseases known to affect >200 million people globally. The scabies mites have shown resistance to the many of currently available chemotherapeutics, a prerequisite to identify potential targets for vaccine development. Paramyosin has been identified as a potential vaccine candidate for parasite control and appears as an important immunogen in S. scabiei. In the present study, we used different immune-informatics tools to analyze S. scabiei paramyosin sequence and screen potential B and T cells epitopes. Epitope prioritization was done based on reference allele coverage, antigenicity, high antigenicity, adhesive ability, non-allergenicity and potential of binding to the DRB*0101 allele. Further, it was ensured that the selected candidates were feasible for experimental cloning and expression analysis. The predicted epitopes were also used in multi-peptide vaccine construction to maximize immunogenicity and efficient recognition and processing by the host immune system. Host immune system dynamics in response to the vaccine construct antigen were also elaborated in silico, revealing robust cellular and humoral immunity. To understand cellular interaction mechanisms, molecular docking followed by molecular dynamic simulation was performed to probe the predominant binding mode of the vaccine construct to the innate immune receptor TLR5. Estimation of binding free energy for the final construct was accomplished and revealed the system highly stable with enriched electrostatic and van der Waals energy. In summary, this study provides a gateway to understand the protein function analysis of a potential vaccine candidate for S. scabiei.

Oxidation of Isodrimeninol with PCC Yields Drimane Derivatives with Activity against Candida Yeast by Inhibition of Lanosterol 14-Alpha Demethylase.

Candida species cause an opportunistic yeast infection called Candidiasis, which is responsible for more than 50,000 deaths every year around the world. Effective treatments against candidiasis caused by non-albicans Candida species such as C. glabrata, C. parapsilosis, C. aureus, and C. krusei are limited due to severe resistance to conventional antifungal drugs. Natural drimane sesquiterpenoids have shown promising antifungal properties against Candida yeast and have emerged as valuable candidates for developing new candidiasis therapies. In this work, we isolated isodrimeninol (C1) from barks of Drimys winteri and used it as starting material for the hemi-synthesis of four sesquiterpenoids by oxidation with pyridinium chlorochromate (PCC). The structure of the products (C2, C3, C4, and C5) was elucidated by 1D and 2D NMR spectroscopy resulting in C4 being a novel compound. Antifungal activity assays against C. albicans, C. glabrata, and C. krusei revealed that C4 exhibited an increased activity (IC50 of 75 μg/mL) compared to C1 (IC50 of 125 μg/mL) in all yeast strains. The antifungal activity of C1 and C4 was rationalized in terms of their capability to inhibit lanosterol 14-alpha demethylase using molecular docking, molecular dynamics simulations, and MM/GBSA binding free energy calculations. In silico analysis revealed that C1 and C4 bind to the outermost region of the catalytic site of 14-alpha demethylase and block the entrance of lanosterol (LAN) to the catalytic pocket. Binding free energy estimates suggested that C4 forms a more stable complex with the enzyme than C1, in agreement with the experimental evidence. Based on this new approach it is possible to design new drimane-type sesquiterpenoids for the control of Candida species as inhibitors of 14-alpha demethylase.

Combining Monte Carlo and Molecular Dynamics Simulations for Enhanced Binding Free Energy Estimation through Markov State Models.

We present a multistep protocol, combining Monte Carlo and molecular dynamics simulations, for the estimation of absolute binding free energies, one of the most significant challenges in computer-aided drug design. The protocol is based on an initial short enhanced Monte Carlo simulation, followed by clustering of the ligand positions, which serve to identify the most relevant states of the unbinding process. From these states, extensive molecular dynamics simulations are run to estimate an equilibrium probability distribution obtained with Markov State Models, which is subsequently used to estimate the binding free energy. We tested the procedure on two different protein systems, the Plasminogen kringle domain 1 and Urokinase, each with multiple ligands, for an aggregated molecular dynamics length of 760 μs. Our results indicate that the initial sampling of the unbinding events largely facilitates the convergence of the subsequent molecular dynamics exploration. Moreover, the protocol is capable to properly rank the set of ligands examined, albeit with a significant computational cost for the, more realistic, Urokinase complexes. Overall, this work demonstrates the usefulness of combining enhanced sampling methods with regular simulation techniques as a way to obtain more reliable binding affinity estimates.

Insights into the mechanism of inhibition of phospholipase A2 by resveratrol: An extensive molecular dynamics simulation and binding free energy calculation

Phospholipase A2 (PLA2) is one of the enzymes involved in the development of cardiovascular diseases, vascular inflammation, risk of heart attacks, and strokes. This enzyme is responsible for catalyzing the hydrolytic cleavage of ester bonds of phospholipids in the biological pathway of inflammation. To prevent the undesired hydrolysis of phospholipids, the catalytic activity of PLA2 needs to be blocked. Resveratrol is a plant-derived polyphenol inhibitor, proven to have anti-inflammatory properties. However, there is still substantial ambiguity about its inhibitory function. The present study uncovers a detailed molecular mechanism behind the resveratrol action in inhibition of PLA2, by applying and comparing two 200-ns molecular dynamics simulations. The results of structural analyses revealed that the binding of resveratrol to PLA2 reduces the content of β-sheets and increases a 5-helix to PLA2 structure, producing more folding and stability in protein. In the active site, the resveratrol is placed between the N-terminal α-helix and the newly formed 5-helix through the hydrophobic interactions with ILE19 and LEU3 residues, as well as the hydrogen bond interactions. These interactions play the role of a network at the entrance of the enzyme active site and prevent the penetration of water molecules into the PLA2 cavity. A high occupancy hydrogen bonding has been identified between SER23 of the protein and hydroxyl group of resveratrol. Furthermore, the estimation of binding free energy verified the binding affinity of resveratrol is thermodynamically sufficient to be stably bounded to PLA2. It also proved that the van der Waals interactions, particularly hydrophobic interactions, have the most significant role in PLA2-resveratrol binding and stability. Overall, our results provide useful information on the stepwise mechanism of the inhibition of PLA2 enzyme by resveratrol, as a target for improving the pharmacological applications.

Mechanistic Study of Potent Fluorinated EGFR Kinase Inhibitors with a Quinazoline Scaffold against L858R/T790M/C797S Resistance Mutation: Unveiling the Fluorine Substituent Cooperativity Effect on the Inhibitory Activity.

Fluorination has considerable potential with regard to the design of kinase inhibitors for anticarcinoma therapy. It was recently reported that fluorination increases the potency of inhibitors of the epidermal growth factor receptor (EGFR), mutations of which have been linked specifically to nonsmall-cell lung cancer. For the L858R/T790M/C797S triplet mutant (EGFRTM), a difluorinated inhibitor, 25g, was found to have 4.23 times greater potency against the EGFRTM than an unfluorinated inhibitor, 25a. This discovery necessitates a rational explanation for the underlying inhibitory mechanisms. Here, we apply multiple computational approaches to explore, validate, and differentiate the binding modes of 25a and 25g in the EGFRTM and investigate the cooperativity effect of fluorine substituents on the inhibitory activity. Our results showed that the EGFRTM in the presence of 25g undergoes a series of conformational changes that favor inhibitor binding to both the active and allosteric sites. Further, the cooperativity effect of fluorine substituents is positive: the complex stability is increased by each additional fluorine substituent. Estimated binding free energies show good correlation with the experimental biological activity. Subsequently, the decomposition energy analysis revealed that the van der Waals interaction is the principal force contributing to variations in the binding affinities of 25a and 25g to the EGFRTM. Per-residue energy-based hierarchical clustering analysis suggests that three hot-spot residues, L718, K745, and D855, are the key in achieving optimal binding modes for 25g with higher affinity in the EGFRTM compared to 25a. This study provides a rationale for the superior EGFRTM-inhibitory potency exhibited by 25g over 25a, which is expected to be useful for the future rational structure-based design of novel EGFRTM inhibitors with improved potency and selectivity.

A Comprehensive In Silico Study Towards Understanding the Inhibitory Mechanism of Lactoperoxidase by Dapsone and Propofol.

Lactoperoxidase (LPO) is a member of the mammalian heme peroxidase family and is an enzyme of the innate immune system. It possesses a covalently linked heme prosthetic group (a derivative of protoporphyrin IX) in its active site. LPO catalyzes the oxidation of halides and pseudohalides in the presence of hydrogen peroxide (H2O2) and shows a broad range of the antimicrobial activity. In this study, we have used two pharmaceutically important drug molecules, namely dapsone and propofol, which were earlier reported as potent inhibitors of LPO. At the same time, the stereochemistry and mode of binding of dapsone and propofol to LPO are still not known because of the lack of the crystal structures of LPO with these two drugs. In order to fill this gap, we utilized molecular docking and molecular dynamics (MD) simulation studies of LPO in its native and complex forms with dapsone and propofol. From the docking results, the estimated binding free energies (ΔG) of -9.25 kcal/mol (Ki = 0.16 μM) and -7.05 kcal/mol (Ki = 6.79 μM) were observed for dapsone, and propofol, respectively. The standard error of the Auto Dock program is 2.5 kcal/mol; therefore, molecular docking results alone were inconclusive. To further validate the docking results, we performed MD simulation on unbound, and two drugs bounded LPO structures. Interestingly, MD simulations results explained that the structural stability of LPO-Propofol complex was higher than LPO-Dapsone complex. The results obtained from this study establish the mode of binding and interaction pattern of the dapsone and propofol to LPO as inhibitors.

Analysis of polyphenolic metabolites from in vitro gastrointestinal digested soft fruit extracts identify malvidin-3-glucoside as an inhibitor of PTP1B

Protein-tyrosine phosphatase 1B (PTP1B, EC 3.1.3.48) is an important regulator of insulin signalling. Herein, we employed experimental and computational biology techniques to investigate the inhibitory properties of phenolics, identified from four in vitro gastrointestinal digested (IVGD) soft fruits, on PTP1B. Analysis by LC-MS/MS identified specific phenolics that inhibited PTP1B in vitro. Enzyme kinetics identified the mode of inhibition, while dynamics, stability and binding mechanisms of PTP1B-ligand complex were investigated through molecular modelling, docking, molecular dynamics (MD) simulations, and MM/PBSA binding free energy estimation. IVGD extracts and specific phenolics identified from the four soft fruits inhibited PTP1B (P < 0.0001) activity. Among the phenolics tested, the greatest inhibition was shown by malvidin-3-glucoside (P < 0.0001) and gallic acid (P < 0.0001). Malvidin-3-glucoside (Ki = 3.8 µg/mL) was a competitive inhibitor and gallic acid (Ki = 33.3 µg/mL) a non-competitive inhibitor of PTP1B. Malvidin-3-glucoside exhibited better binding energy than gallic acid and the synthetic inhibitor Dephostatin (−7.38 > −6.37 > −5.62 kcal/mol) respectively. Principal component analysis demonstrated malvidin-3-glucoside PTP1B-complex occupies more conformational space where critical WPD-loop displayed a higher degree of motion. MM/PBSA binding free energy for malvidin-3-glucoside to PTP1B was found to be higher than other complexes mediated by Van der Waals energy rather than electrostatic interaction for the other two inhibitors (-80.32 ± 1.25 > −40.64 ± 1.43 > −21.63 ± 1.73 kcal/mol) respectively. Altogether, we have established novel insights into the specific binding of dietary phenolics and have identified malvidin-3-glucoside as an PTP1B inhibitor, which may be further industrially developed for the treatment of type-2 diabetes.

Natural compounds from Clerodendrum spp. as possible therapeutic candidates against SARS-CoV-2: An in silico investigation

The COVID-19 pandemic caused by the novel coronavirus SARS-CoV-2 has rattled global public health, with researchers struggling to find specific therapeutic solutions. In this context, the present study employed an in silico approach to assess the inhibitory potential of the phytochemicals obtained from GC-MS analysis of twelve Clerodendrum species against the imperative spike protein, main protease enzyme Mpro and RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2. An extensive molecular docking investigation of the phytocompounds at the active binding pockets of the viral proteins revealed promising inhibitory potential of the phytochemicals taraxerol, friedelin and stigmasterol. Decent physicochemical attributes of the compounds in accordance with Lipinski’s rule of five and Veber’s rule further established them as potential therapeutic candidates against SARS-CoV-2. Molecular mechanics-generalized Born surface area (MM-GBSA) binding free energy estimation revealed that taraxerol was the most promising candidate displaying the highest binding efficacy with all the concerned SARS-CoV-2 proteins included in the present analysis. Our observations were supported by robust molecular dynamics simulations of the complexes of the viral proteins with taraxerol for a timescale of 40 nanoseconds. It was striking to note that taraxerol exhibited better binding energy scores with the concerned viral proteins than the drugs that are specifically targeted against them. The present results promise to provide new avenues to further evaluate the potential of the phytocompound taraxerol in vitro and in vivo towards its successful deployment as a SARS-CoV-2 inhibitor and combat the catastrophic COVID-19. Communicated by Ramaswamy H. Sarma

Conformational transition of Acinetobacter baumannii KdsC enzyme and the role of magnesium in binding: An insight from comparative molecular dynamics simulation and its implications in novel antibiotics design

The 3-deoxy-d-manno-octulosonate 8-phosphate phosphatase (KdsC) catalyzes the hydrolysis of 3-deoxy-d-manno-octulosonate 8-phosphate (KDO 8-P) to 3-deoxy-d-manno-octulosonate (KDO) and inorganic phosphate in KDO biosynthesis pathway of Gram-negative bacteria lipopolysaccharide (LPS) hydrophobic lipid-A core. The essentiality of KDO for bacterial cell viability presents the possibility of its targeting to develop broad-spectrum antibacterial agents. In this study, a receptor based virtually screening method was put forward to identify novel lead inhibitory molecules for KdsC enzyme. Dynamics evaluation in solution revealed three complexes: Asinex-1197, Asinex-1705, and Asinex-1710 from Asinex antibacterial library as highly stable, involving conformational transition from open to close upon lead molecules binding and eloquent role of active pocket magnesium towards inhibitors binding and movements. Interconversion of local secondary structure elements in sequence region of Asp192-Asp208 covering motif β-turn, β-hairpin, and β-sheets is seen recurrently that could be in all likelihood of the pressure excreted on this region during closing conformation event or magnesium driven inhibitor adjustments. The binding free energy estimation predicted gas phase energy for all the three complexes dominating with major contribution from van der Waals energy (in case of Asinex-1705 and Asinex-1710) and balanced contributions of both electrostatic and van der Waals (in case of Asinex-1197). Key residues-scanning shortlisted Leu45, Asp185, Gy188, Arg231, and Lys255 as vital in the interaction network of magnesium and inhibitors at the binding site. Their crucial roles in net binding energy were reaffirmed via in silico site directed alanine scanning method. The filtered hits might be useful to further scaffolds addition and structural optimization to yield high affinity binders of KdsC enzyme, whose inhibition, in turn, will disrupt the outer membrane synthesis.

Ranking of Ligand Binding Kinetics Using a Weighted Ensemble Approach and Comparison with a Multiscale Milestoning Approach.

To improve lead optimization efforts in finding the right ligand, pharmaceutical industries need to know the ligand's binding kinetics, such as binding and unbinding rate constants, which often correlate with the ligand's efficacy in vivo. To predict binding kinetics efficiently, enhanced sampling methods, such as milestoning and the weighted ensemble (WE) method, have been used in molecular dynamics (MD) simulations of these systems. However, a comparison of these enhanced sampling methods in ranking ligands has not been done. Hence, a WE approach called the concurrent adaptive sampling (CAS) algorithm that uses MD simulations was used to rank seven ligands for β-cyclodextrin, a system in which a multiscale milestoning approach called simulation enabled estimation of kinetic rates (SEEKR) was also used, which uses both MD and Brownian dynamics simulations. Overall, the CAS algorithm can successfully rank ligands using the unbinding rate constant koff values and binding free energy ΔG values, as SEEKR did, with reduced computational cost that is about the same as SEEKR. We compare the CAS algorithm simulations with different parameters and discuss the impact of parameters in ranking ligands and obtaining rate constant and binding free energy estimates. We also discuss similarities and differences and advantages and disadvantages of SEEKR and the CAS algorithm for future use.

Efficient Estimation of Absolute Binding Free Energy for a Homeodomain-DNA Complex from Nonequilibrium Pulling Simulations.

Estimation of binding free energies is one of the central aims of simulations of biomolecular complexes. We explore the accuracy and efficiency of setups based on nonequilibrium pulling simulations applied to the estimation of binding affinities of DNA-binding proteins. Absolute binding free energies are calculated over a range of temperatures and compared to results obtained previously using an equilibrium method. We show that realistic binding affinities can be obtained with the presented nonequilibrium approach, which also entails lower computational requirements. Errors of the binding free energy estimates are investigated and are shown to be comparable to those observed previously. Bounds are provided on the convergence of the errors with respect to the number of pulling simulations performed and with respect to the applied pull rate.