Two enzyme conformations (with shifted domains III and significant differences in the catalytic site geometries) were obtained. protomer in Alexidine dihydrochloride the asymmetric homodimer has the correct conformation to perform catalysis. Shi and Song  conducted a series of experiments on site-directed mutants of SARS 3CLpro, investigating the monomer-dimer equilibrium and enzymatic activity. They identified four regions associated with the enzyme Alexidine dihydrochloride dimerization C residues 1C5 from the demonstrated that Arg298Ala mutation in the SARS main protease completely stops the dimerization, resulting in an inactive monomeric form of the enzyme. On the other hand, a triple Ser284Ala, Thr285Ala and Ile286Ala mutant has a slightly enhanced dimerization capability and shows a 3.6-fold increase in the activity, compared with the wild-type protease . Two mutations (Thr285Ala and Ile286Leu) observed in SARS-CoV-2 lead to a closer packing of the dimer with a slight increase in the catalytic efficiency, but without influencing the dimer dissociation . Open in a separate window Figure 1. Structure of SARS-CoV-2 3CLpro (PDB ID: 6LU7).The conducted a virtual screening of 8000 drugs from available libraries, with SARS-CoV 3CLpro as the receptor. They identified prulifloxacin, bictegravir, nelfinavir and tegobuvir as safe and potential 3CLpro inhibitors. While prulifloxacin binds to the active site, other compounds have higher binding potential for the joint groove site . Preliminary results of Sekhar’s virtual screening of 3639 approved drugs and the SARS-CoV-2 3CLpro suggest that saquinavir and beclabuvir are also potential candidates for COVID-19 therapy . Insilico Medicine  used its generative chemistry pipeline to design novel drug-like inhibitors. Their approach included a crystal-derived pocket-based generator, a homology modeling-based generation?and a ligand-based generation. By 15?April 2020, 97 novel potential inhibitors of SARS-CoV-2 main protease had been generated. ul Qamar adopted a different approach . After constructing a 3D homology model, they screened it against a medicinal plant library containing phytochemicals and traditional Chinese medicinal compounds. Among 32,297 phytocompounds, 5,7,3,4-tetrahydroxy-2-(3,3-dimethylallyl) isoflavone, an isoflavone extracted from pinpointed to the Ser 139-Phe 140-Leu 141 loop, whose transformation to a short 310-helix disrupts the catalytic machinery in the inactive monomer structure . Our analysis showed that the mean distances between the Asn 142 CG atom types (close to both the Cys 145 residue and the Ser 139-Phe 140-Leu 141 fragment) and Glu 166, as well as the distance between the His 41 ring centroid and the Gln 189 CA atom are shorter in the B conformation, making the A conformation’s catalytic pocket wider on average. The greatest difference is in the mean distances between the His 41 centroid and the Met 49 SD Mouse monoclonal to GATA1 atom type, where the position and the orientation of the short helix influences the His 41 imidazole ring orientation. Docking experiments The microbial natural products from the Natural Products Atlas that satisfied selection filters were docked to two SARS-CoV-2 3CLpro conformations, obtained by a MD simulation (as described in the previous section). The weighted docking score was calculated according to Equation 1. The average weighted docking score was 6.1??0.9 kcal mol-1. To further filter the potential hit molecules, we implemented criteria based on ADMET properties: not a cytochrome P450 inhibitor (predicted for CYP1A2, CYP2C9, CYP2D6, and CYP3A4 enzymes), not a P-glycoprotein I/II inhibitor, nontoxic (not an Alexidine dihydrochloride inhibitor of hERG I/II), noncancerogenic (AMES negative)?and nonhepatotoxic. Besides the constrains imposed on molecules from the Natural Products Atlas to qualify for docking (molecular weight and number of rotatable bonds), additional criteria for oral bioavailability were also implemented: lipophilicity (logP)? 5; hydrogen bond acceptor sites 10; and 3) hydrogen donor sites 5. After employing all these criteria, top eight molecules with best docking scores satisfying all criteria were collected in Table?1 (the complete list with all the tested molecules can be found in Supplementary Table 3). Table 1. Hit molecules from the Natural Products Atlas, as potential SARS-CoV-2 3CLpro inhibitors. reported that ECFP offers the highest precision on average, according to database search by compound similarity based on FP . Hence, in our analysis, ECFP was used for the identification of the top lead molecule based on its resemblance to the DrugBank molecules. The release of DrugBank used in the present study (version 5.1.5) contains almost 9000 drug entries including approved small molecule drugs, approved biologics, nutraceuticals and experimental drugs . Futalosine, a secondary metabolite isolated from the genus of Actinobacteria, was found to have the highest Tanimoto molecular similarity index (. The eight hit molecules were.