Molecular Interactions of Tannic Acid with Proteins Associated with SARS-CoV-2 Infectivity.

The overall impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on our society is unprecedented. The identification of small natural ligands that could prevent the entry and/or replication of the coronavirus remains a pertinent approach to fight the coronavirus disease (COVID-19) pandemic. Previously, we showed that the phenolic compounds corilagin and 1,3,6-tri-O-galloyl-ß-D-glucose (TGG) inhibit the interaction between the SARS-CoV-2 spike protein receptor binding domain (RBD) and angiotensin-converting enzyme 2 (ACE2), the SARS-CoV-2 target receptor on the cell membrane of the host organism. Building on these promising results, we now assess the effects of these phenolic ligands on two other crucial targets involved in SARS-CoV-2 cell entry and replication, respectively: transmembrane protease serine 2 (TMPRSS2) and 3-chymotrypsin like protease (3CLpro) inhibitors. Since corilagin, TGG, and tannic acid (TA) share many physicochemical and structural properties, we investigate the binding of TA to these targets. In this work, a combination of experimental methods (biochemical inhibition assays, surface plasmon resonance, and quartz crystal microbalance with dissipation monitoring) confirms the potential role of TA in the prevention of SARS-CoV-2 infectivity through the inhibition of extracellular RBD/ACE2 interactions and TMPRSS2 and 3CLpro activity. Moreover, molecular docking prediction followed by dynamic simulation and molecular mechanics Poisson-Boltzmann surface area (MMPBSA) free energy calculation also shows that TA binds to RBD, TMPRSS2, and 3CLpro with higher affinities than TGG and corilagin. Overall, these results suggest that naturally occurring TA is a promising candidate to prevent and inhibit the infectivity of SARS-CoV-2.

Punicalagin and zinc (II) ions inhibit the activity of SARS-CoV-2 3CL-protease in vitro.

OBJECTIVE: Coronavirus 2019 (COVID-19) has now been declared as a worldwide pandemic. Currently, no drugs have been endorsed for its treatment; in this manner, a pressing need has been developed for any antiviral drugs that will treat COVID-19. Coronaviruses require the SARS-CoV-2 3CL-Protease (3CL-protease) for cleavage of its polyprotein to yield a single useful protein and assume a basic role in the disease progression. In this study, we demonstrated that punicalagin, the fundamental active element of pomegranate in addition to the combination of punicalagin with zinc (Zn) II, appear to show powerful inhibitory activity against SARS-CoV-2. MATERIALS AND METHODS: The 3CL protease assay kit was used to quantify 3CL protease action. The tetrazolium dye, MTS, was used to evaluate cytotoxicity. RESULTS: Punicalagin showed inhibitory action against the 3CL-protease in a dose-dependent manner, and IC50 was found to be 6.192 µg/ml for punicalagin. Punicalagin (10 µg/mL) demonstrated a significant inhibitory activity toward 3CL-protease activity (p < 0.001), yet when punicalagin is combined with zinc sulfate monohydrate (punicalagin/Zn-II) extremely strong 3CL-protease activity (p < 0.001) was obtained. The action of 3CL-protease with punicalagin/Zn-II was decreased by approximately 4.4-fold in contrast to only punicalagin (10 µg/mL). Likewise, we did not notice any significant cytotoxicity caused by punicalagin, Zn-II, or punicalagin/Zn-II. CONCLUSIONS: We suggest that these compounds could be used as potential antiviral drugs against COVID-19.

The inhibitory effects of PGG and EGCG against the SARS-CoV-2 3C-like protease.

The coronavirus disease (COVID-19) pandemic, resulting from human-to-human transmission of a novel severe acute respiratory syndrome coronavirus (SARS-CoV-2), has led to a global health crisis. Given that the 3 chymotrypsin-like protease (3CLpro) of SARS-CoV-2 plays an indispensable role in viral polyprotein processing, its successful inhibition halts viral replication and thus constrains virus spread. Therefore, developing an effective SARS-CoV-2 3CLpro inhibitor to treat COVID-19 is imperative. A fluorescence resonance energy transfer (FRET)-based method was used to assess the proteolytic activity of SARS-CoV-2 3CLpro using intramolecularly quenched fluorogenic peptide substrates corresponding to the cleavage sequence of SARS-CoV-2 3CLpro. Molecular modeling with GEMDOCK was used to simulate the molecular interactions between drugs and the binding pocket of SARS-CoV-2 3CLpro. This study revealed that the Vmax of SARS-CoV-2 3CLpro was about 2-fold higher than that of SARS-CoV 3CLpro. Interestingly, the proteolytic activity of SARS-CoV-2 3CLpro is slightly more efficient than that of SARS-CoV 3CLpro. Meanwhile, natural compounds PGG and EGCG showed remarkable inhibitory activity against SARS-CoV-2 3CLpro than against SARS-CoV 3CLpro. In molecular docking, PGG and EGCG strongly interacted with the substrate binding pocket of SARS-CoV-2 3CLpro, forming hydrogen bonds with multiple residues, including the catalytic residues C145 and H41. The activities of PGG and EGCG against SARS-CoV-2 3CLpro demonstrate their inhibition of viral protease activity and highlight their therapeutic potentials for treating SARS-CoV-2 infection.