SAR, Molecular Docking and Molecular Dynamic Simulation of Natural Inhibitors against SARS-CoV-2 Mpro Spike Protein

The SARS-CoV-2 virus and its mutations have affected human health globally and created significant danger for the health of people all around the world. To cure this virus, the human Angiotensin Converting Enzyme-2 (ACE2) receptor, the SARS-CoV-2 main protease (Mpro), and spike proteins were found to be likely candidates for the synthesis of novel therapeutic drug. In the past, proteins were capable of engaging in interaction with a wide variety of ligands, including both manmade and plant-derived small molecules. Pyrus communis L., Ginko bibola, Carica papaya, Syrian rue, and Pimenta dioica were some of the plant species that were studied for their tendency to interact with SARS-CoV-2 main protease (Mpro) in this research project (6LU7). This scenario investigates the geometry, electronic, and thermodynamic properties computationally. Assessing the intermolecular forces of phytochemicals with the targets of the SARS-CoV-2 Mpro spike protein (SP) resulted in the recognition of a compound, kaempferol, as the most potent binding ligand, -7.7 kcal mol-1. Kaempferol interacted with ASP-187, CYS-145, SER-144, LEU 141, MET-165, and GLU-166 residues. Through additional molecular dynamic simulations, the stability of ligand-protein interactions was assessed for 100 ns. GLU-166 remained intact with 33% contact strength with phenolic OH group. We noted a change in torsional conformation, and the molecular dynamics simulation showed a potential variation in the range from 3.36 to 7.44 against a 45-50-degree angle rotation. SAR, pharmacokinetics, and drug-likeness characteristic investigations showed that kaempferol may be the suitable candidate to serve as a model for designing and developing new anti-COVID-19 medicines.

Phytoestrogen β-Sitosterol Exhibits Potent In Vitro Antiviral Activity against Influenza A Viruses

Influenza is a contagious infection in humans that is caused frequently by low pathogenic seasonal influenza viruses and occasionally by pathogenic avian influenza viruses (AIV) of H5, H7, and H9 subtypes. Recently, the clinical sector in poultry and humans has been confronted with many challenges, including the limited number of antiviral drugs and the rapid evolution of drug-resistant variants. Herein, the anti-influenza activities of various plant-derived phytochemicals were investigated against highly pathogenic avian influenza A/H5N1 virus (HPAIV H5N1) and seasonal low pathogenic human influenza A/H1N1 virus (LPHIV H1N1). Out of the 22 tested phytochemicals, the steroid compounds β-sitosterol and β-sitosterol-O-glucoside have very potent activity against the predefined influenza A viruses (IAV). Both steroids could induce such activity by affecting multiple stages during IAV replication cycles, including viral adsorption and replication with a major and significant impact on the virus directly in a cell-free status "viricidal effect". On a molecular level, several molecular docking studies suggested that β-sitosterol and β-sitosterol-O-glucoside exhibited viricidal effects through blocking active binding sites of the hemagglutinin surface protein, as well as showing inhibitory effects against replication through the binding with influenza neuraminidase activity and blocking the active sites of the M2 proton channel activity. The phytoestrogen β-sitosterol has structural similarity with the active form of the female sex hormone estradiol, and this similarity is likely one of the molecular determinants that enables the phytoestrogen β-sitosterol and its derivative to control IAV infection in vitro. This promising anti-influenza activity of β-sitosterol and its O-glycoside derivative, according to both in vitro and cheminformatics studies, recommend both phytochemicals for further studies going through preclinical and clinical phases as efficient anti-influenza drug candidates.

Effect of Date Palm (Phoenix dactylifera) Phytochemicals on Aβ1-40 Amyloid Formation: An in-silico Analysis

Alzheimer's disease (AD) is a neurodegenerative disease and the most prevalent form of dementia. The generation of oxygen free radicals and oxidative damage is believed to be involved in the pathogenesis of AD. It has been suggested that date palm, a plant rich in phenolic compounds and flavonoids, can provide an alternative treatment to fight memory loss and cognitive dysfunction due to its potent antioxidant activity. Thus, we studied the effect of flavonoids present in date palm on Aβ1-40 amyloid formation using molecular docking and molecular dynamics simulation. AutoDock. Myricetin was used as a positive control drug. The flavonoids Diosmetin, Luteolin, and Rutin were found to be potent inhibitors of aggregation (docking energies ≤ -8.05 kcal mol-1) targeting Aβ1-40 fibrils (both 2LMO and 6TI5), simultaneously. Further screening by physicochemical properties and drug-likeness analysis suggested that all flavonoids except Rutin followed Lipinski's rule of five. Rutin was, thus, taken as a negative control (due to its violation of Lipinski's rule) to compare its dynamics with Diosmetin. Diosmetin exhibited the highest positive scores for drug likeness. Since Luteolin exhibited moderate drug-likeness and better absorption properties, it was also included in molecular dynamics simulation. Molecular dynamics of shortlisted compounds (Rutin, Diosmetin, and Luteolin) were performed for 200 ns, and the results were analyzed by monitoring root mean square deviations (RMSD), root mean square fluctuation (RMSF) analysis, the radius of gyration (Rg), and solvent accessible surface area (SASA). The results proved the formation of a stable protein-compound complex. Based on binding energies and non-bonded interactions, Rutin and Luteolin emerged as better lead molecules than Diosmetin. However, high MW (610.5), lowest absorption rate (16.04%), and more than one violation of Lipinski's rule make Rutin a less likely candidate as an anti-amyloidogenic agent. Moreover, among non-violators of Lipinski's rule, Diosmetin exhibited a greater absorption rate than Luteolin as well as the highest positive scores for drug-likeness. Thus, we can conclude that Diosmetin and Luteolin may serve as a scaffold for the design of better inhibitors with higher affinities toward the target proteins. However, these results warrant in-vitro and in-vivo validation before practical use.

Structural and inhibitory effects of fulvic and humic acids against tyrosinase

Inhibition of tyrosinase activity can control fruit browning and preserve the flavor and nutritional value of food. The impacts of fulvic acid (FA) and humic acid (HA) on tyrosinase activity were investigated utilizing circular dichroism (CD) and fluorescence spectroscopy, molecular docking (MD), and molecular dynamics simulations. HA and FA demonstrated a mixed type of inhibition with K_i 2.02 and 5.2 μM, respectively. The thermodynamic parameters displayed that the hydrogen bond and hydrophobic force play a major role in the FA-tyrosinase and HA-tyrosinase interaction, respectively. Fluorescence experiments demonstrated changes in tyrosinase tertiary structures. HA could not destroy the tyrosinase secondary structure significantly, however, FA has a significant influence on the tyrosinase secondary structure. The molecular dynamics findings demonstrated the minimal fluctuations and the lowest flexibility in the complex amino acids in the HA-tyrosinase and FA-tyrosinase interaction. Altogether, HA and FA could be utilized in food industries as an accessible natural source for tyrosinase inhibition. PRACTICAL APPLICATIONS: Recently, the investigation of tyrosinase inhibitors from the biosphere for hindrance of undesired browning in the food industry has increased considerably. Mushroom tyrosinase is a suitable model for kinetic research owing to its availability as well as close conformational similarity to tyrosinase in a mammal. Natural sources and their effective compounds could have wonderful potential on tyrosinase activity and structure, thus, in this study, the interactions between tyrosinase and fulvic acid (FA) and Humic acid (HA) were investigated. Previously, it has been shown that HA and FA have antioxidant properties and they can improve the quality of food via retarding lipid oxidation. Altogether, further investigations are warranted to draw firm conclusions, HA and FA could be utilized in food industries not only as antioxidant agents but also as an accessible natural source for tyrosinase inhibition.