The SARS CoV-2 pandemic has affected millions of people around the globe. Despite many efforts to find some effective medicines against SARS CoV-2, no established therapeutics are available yet. The use of phytochemicals as antiviral agents provides hope against the proliferation of SARS-CoV-2. Several natural compounds were analyzed by virtual screening against six SARS CoV-2 protein targets using molecular docking simulations in the present study. More than a hundred plant-derived secondary metabolites have been docked, including alkaloids, flavonoids, coumarins, and steroids. SARS CoV-2 protein targets include Main protease (MPro), Papain-like protease (PLpro), RNA-dependent RNA polymerase (RdRp), Spike glycoprotein (S), Helicase (Nsp13), and E-Channel protein. Phytochemicals were evaluated by molecular docking, and MD simulations were performed using the YASARA structure using a modified genetic algorithm and AMBER03 force field. Binding energies and dissociation constants allowed the identification of potentially active compounds. Ligand-protein interactions provide an insight into the mechanism and potential of identified compounds. Glycyrrhizin and its metabolite 18-β-glycyrrhetinic acid have shown a strong binding affinity for MPro, helicase, RdRp, spike, and E-channel proteins, while a flavonoid Baicalin also strongly binds against PLpro and RdRp. The use of identified phytochemicals may help to speed up the drug development and provide natural protection against SARS-CoV-2.

Streptococcus thermophilus is used primarily as starter cultures to counter the harmful bacteria grown in cheese and yogurt making/preservation processes. These bacteria produce some exogenous toxins called bacteriocins having the antimicrobial activities against both Gram positive and Gram negative bacteria. In our study S. thermophilus growth was obtained at pH 5.5 and temperature 40°C. Bacteriocin activities were checked after their treatment with different enzymes, organic solvents, sodium chloride (NaCl) and detergents as well as their heat stability and effect of pH was studied. Bacteriocin activity was found heat stable at 100°C for 30 min and was found stable in the 3-10 pH range but lost the activity after the treatment with proteinase-K and protease enzymes. Activity was lost in treatment with lipase and amylase which shows the presence of lipo-glycolated peptide. Bacteriocin activity was lost on the presence of Dithiothreitol (DTT) and β β β β-mercaptoethanol which showed the presence of disulphide bond present in bacteriocin and essential for its activity. Urea and ethylene diamine tetraacetic acid (EDTA) also affected the bacteriocin activity but found stable to survive in the presence of 6% NaCl. Antibacterial assay showed the strong growth inhibition of test bacteria. Bactericidal activity was further purified to homogeneity by ammonium sulphate precipitation and different chromatographic techniques. Molecular weight was calculated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as 2.7 kDa.

A structurally novel chitinase, Tc-ChiD, was identified from the hyperthermophilic archaeon Thermococcus chitonophagus, which can grow on chitin as the sole organic carbon source. The gene encoding Tc-ChiD contains regions corresponding to a signal sequence, two chitin-binding domains, and a putative catalytic domain. This catalytic domain shows no similarity with previously characterized chitinases but resembles an uncharacterized protein found in the mesophilic anaerobic bacterium Clostridium botulinum. Two recombinant Tc-ChiD proteins were produced in Escherichia coli, one without the signal sequence [TcChiD(⌬S)] and the other corresponding only to the putative catalytic domain [Tc-ChiD(⌬BD)]. Enzyme assays using N-acetylglucosamine (GlcNAc) oligomers indicated that both proteins hydrolyze GlcNAc oligomers longer than (GlcNAc) 4 . Chitinase assays using colloidal chitin suggested that Tc-ChiD is an exo-type chitinase that releases (GlcNAc) 2 or (GlcNAc) 3 . Analysis with GlcNAc oligomers modified with p-nitrophenol suggested that Tc-ChiD recognizes the reducing end of chitin chains. While TcChiD(⌬BD) displayed a higher initial velocity than that of Tc-ChiD(⌬S), we found that the presence of the two chitin-binding domains significantly enhanced the thermostability of the catalytic domain. In T. chitonophagus, another chitinase ortholog that is similar to the Thermococcus kodakarensis chitinase ChiA is present and can degrade chitin from the nonreducing ends. Therefore, the presence of multiple chitinases in T. chitonophagus with different modes of cleavage may contribute to its unique ability to efficiently degrade chitin. IMPORTANCEA structurally novel chitinase, Tc-ChiD, was identified from Thermococcus chitonophagus, a hyperthermophilic archaeon. The protein contains a signal peptide for secretion, two chitin-binding domains, and a catalytic domain that shows no similarity with previously characterized chitinases. Tc-ChiD thus represents a new family of chitinases. Tc-ChiD is an exo-type chitinase that recognizes the reducing end of chitin chains and releases (GlcNAc) 2 or (GlcNAc) 3 . As a thermostable chitinase that recognizes the reducing end of chitin chains was not previously known, Tc-ChiD may be useful in a wide range of enzyme-based technologies to degrade and utilize chitin. Chitin is a ␤-1,4-linked insoluble linear polymer of N-acetylglucosamine (GlcNAc) and is the main component of the exoskeleton of crustaceans and insects, as well as the cell walls of fungi. Chitin is the second most abundant natural polysaccharide after cellulose, and its annual formation rate is in the order of 10 10 to 10 11 tons (1). At present, the majority of chitin remains unused, and thus the development of effective methods to convert chitin into useful biomaterials and/or bioenergy is important to maintain our supplies of edible polysaccharides, such as starch.Chitinases are enzymes responsible for the hydrolysis of chitin polymer, and they produce GlcNAc and/or its oligomers as products. Chitinases are found ...

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