SARS-CoV-2 polyprotein substrate regulates the stepwise Mpro cleavage reaction.

The processing of the Coronavirus polyproteins pp1a and pp1ab by the main protease Mpro to produce mature proteins is a crucial event in virus replication and a promising target for antiviral drug development. Mpro cleaves polyproteins in a defined order, but how Mpro and/or the polyproteins determine the order of cleavage remains enigmatic due to a lack of structural information about polyprotein-bound Mpro. Here, we present the cryo-EM structures of SARS-CoV-2 Mpro in an apo form and in complex with the nsp7-10 region of the pp1a polyprotein. The complex structure shows that Mpro interacts with only the recognition site residues between nsp9 and nsp10, without any association with the rest of the polyprotein. Comparison between the apo form and polyprotein-bound structures of Mpro highlights the flexible nature of the active site region of Mpro, which allows it to accommodate ten recognition sites found in the polyprotein. These observations suggest that the role of Mpro in selecting a preferred cleavage site is limited and underscores the roles of the structure, conformation, and/or dynamics of the polyproteins in determining the sequence of polyprotein cleavage by Mpro.

Multi-level scoring approach to discover multi-targeting potency of medicinal plant phytochemicals against protein targets in SARS-CoV-2 and human ACE-2 receptor

SARS-CoV-2 pandemic has become a major threat to human healthcare and world economy. Due to the rapid spreading and deadly nature of infection, we are in a situation to develop quick therapeutics to combat SARS-CoV-2. In this study, we have adopted a multi-level scoring approach to identify multi-targeting potency of bioactive compounds in selected medicinal plants and compared its efficacy with two reference drugs, Nafamostat and Acalabrutinib which are under clinical trials to treat SARS-CoV-2. In particular, we employ molecular docking and implicit solvent free energy calculations (as implemented in the Molecular Mechanics-Generalized Born Surface Area approach) and QM fragmentation approach for validating the potency of bioactive compounds from the selected medicinal plants against four different viral targets and one human receptor (Angiotensin-converting enzyme 2-ACE-2) which facilitates the SARS-CoV-2 entry into the cell. The protein targets considered for the study are viral 3CL main protease (3CLpro), papain-like protease (PLpro), RNA dependent RNA polymerase (RdRp), and viral spike protein-human hACE-2 complex (Spike:hACE2) including human protein target (hACE-2). Herein, there liable multi-level scoring approach was used to validate the mechanism behind the multi-targeting potency of selected phytochemicals from medicinal plants. The present study evidenced that the phytochemicals Chebulagic acid, Stigmosterol, Repandusinic acid and Geranin exhibited efficient inhibitory activity against PLpro while Chebulagic acid was highly active against 3CLpro. Chebulagic acid and Geranin also showed excellent target specific activity against RdRp. Luteolin, Quercetin, Chrysoeriol and Repandusinic acid inhibited the interaction of viral spike protein with human ACE-2 receptor. Moreover, Piperlonguminine and Piperine displayed significant inhibitory activity against human ACE-2 receptor. Therefore, the identified compounds namely Chebulagic acid, Geranin and Repandusinic acid can serve as potent multi-targeting phytomedicine for treating COVID-19. © 2022, National Institute of Science Communication and Policy Research. All rights reserved.

Potential drugs against COVID-19 revealed by gene expression profile, molecular docking and molecular dynamic simulation.

Aim: SARS-CoV-2, an emerging betacoronavirus, is the causative agent of COVID-19. Currently, there are few specific and selective antiviral drugs for the treatment and vaccines to prevent contagion. However, their long-term effects can be revealed after several years, and new drugs for COVID-19 should continue to be investigated. Materials & methods: In the first step of our study we identified, through a gene expression analysis, several drugs that could act on the biological pathways altered in COVID-19. In the second step, we performed a docking simulation to test the properties of the identified drugs to target SARS-CoV-2. Results: The drugs that showed a higher binding affinity are bardoxolone (-8.78 kcal/mol), irinotecan (-8.40 kcal/mol) and pyrotinib (-8.40 kcal/mol). Conclusion: We suggested some drugs that could be efficient in treating COVID-19.

Room-temperature X-ray crystallography reveals the oxidation and reactivity of cysteine residues in SARS-CoV-2 3CL Mpro: insights into enzyme mechanism and drug design.

The emergence of the novel coronavirus SARS-CoV-2 has resulted in a worldwide pandemic not seen in generations. Creating treatments and vaccines to battle COVID-19, the disease caused by the virus, is of paramount importance in order to stop its spread and save lives. The viral main protease, 3CL Mpro, is indispensable for the replication of SARS-CoV-2 and is therefore an important target for the design of specific protease inhibitors. Detailed knowledge of the structure and function of 3CL Mpro is crucial to guide structure-aided and computational drug-design efforts. Here, the oxidation and reactivity of the cysteine residues of the protease are reported using room-temperature X-ray crystallography, revealing that the catalytic Cys145 can be trapped in the peroxysulfenic acid oxidation state at physiological pH, while the other surface cysteines remain reduced. Only Cys145 and Cys156 react with the alkylating agent N-ethylmaleimide. It is suggested that the zwitterionic Cys145-His45 catalytic dyad is the reactive species that initiates catalysis, rather than Cys145-to-His41 proton transfer via the general acid-base mechanism upon substrate binding. The structures also provide insight into the design of improved 3CL Mpro inhibitors.

Structure-guided design of a perampanel-derived pharmacophore targeting the SARS-CoV-2 main protease.

There is a clinical need for direct-acting antivirals targeting SARS-CoV-2, the coronavirus responsible for the COVID-19 pandemic, to complement current therapeutic strategies. The main protease (Mpro) is an attractive target for antiviral therapy. However, the vast majority of protease inhibitors described thus far are peptidomimetic and bind to the active-site cysteine via a covalent adduct, which is generally pharmacokinetically unfavorable. We have reported the optimization of an existing FDA-approved chemical scaffold, perampanel, to bind to and inhibit Mpro noncovalently with IC50s in the low-nanomolar range and EC50s in the low-micromolar range. Here, we present nine crystal structures of Mpro bound to a series of perampanel analogs, providing detailed structural insights into their mechanism of action and structure-activity relationship. These insights further reveal strategies for pursuing rational inhibitor design efforts in the context of considerable active-site flexibility and potential resistance mechanisms.

Malleability of the SARS-CoV-2 3CL Mpro Active-Site Cavity Facilitates Binding of Clinical Antivirals.

The COVID-19 pandemic caused by SARS-CoV-2 requires rapid development of specific therapeutics and vaccines. The main protease of SARS-CoV-2, 3CL Mpro, is an established drug target for the design of inhibitors to stop the virus replication. Repurposing existing clinical drugs can offer a faster route to treatments. Here, we report on the binding mode and inhibition properties of several inhibitors using room temperature X-ray crystallography and in vitro enzyme kinetics. The enzyme active-site cavity reveals a high degree of malleability, allowing aldehyde leupeptin and hepatitis C clinical protease inhibitors (telaprevir, narlaprevir, and boceprevir) to bind and inhibit SARS-CoV-2 3CL Mpro. Narlaprevir, boceprevir, and telaprevir are low-micromolar inhibitors, whereas the binding affinity of leupeptin is substantially weaker. Repurposing hepatitis C clinical drugs as COVID-19 treatments may be a useful option to pursue. The observed malleability of the enzyme active-site cavity should be considered for the successful design of specific protease inhibitors.

Unusual zwitterionic catalytic site of SARS-CoV-2 main protease revealed by neutron crystallography.

The main protease (3CL Mpro) from SARS-CoV-2, the etiological agent of COVID-19, is an essential enzyme for viral replication. 3CL Mpro possesses an unusual catalytic dyad composed of Cys145 and His41 residues. A critical question in the field has been what the protonation states of the ionizable residues in the substrate-binding active-site cavity are; resolving this point would help understand the catalytic details of the enzyme and inform rational drug development against this pernicious virus. Here, we present the room-temperature neutron structure of 3CL Mpro, which allowed direct determination of hydrogen atom positions and, hence, protonation states in the protease. We observe that the catalytic site natively adopts a zwitterionic reactive form in which Cys145 is in the negatively charged thiolate state and His41 is doubly protonated and positively charged, instead of the neutral unreactive state usually envisaged. The neutron structure also identified the protonation states, and thus electrical charges, of all other amino acid residues and revealed intricate hydrogen-bonding networks in the active-site cavity and at the dimer interface. The fine atomic details present in this structure were made possible by the unique scattering properties of the neutron, which is an ideal probe for locating hydrogen positions and experimentally determining protonation states at near-physiological temperature. Our observations provide critical information for structure-assisted and computational drug design, allowing precise tailoring of inhibitors to the enzyme's electrostatic environment.

FDA-approved thiol-reacting drugs that potentially bind into the SARS-CoV-2 main protease, essential for viral replication.

Emergent novel SARS-CoV-2 is responsible for the current pandemic outbreak of severe acute respiratory syndrome with high mortality among the symptomatic population worldwide. Given the absence of a current vaccine or specific antiviral treatment, it is urgent to search for FDA-approved drugs that can potentially inhibit essential viral enzymes. The inhibition of 3CLpro has potential medical application, due to the fact that it is required for processing of the first translated replicase polyproteins into a series of native proteins, which are essential for viral replication in the host cell. We employed an in silico approach to test if disulfiram, as well as its metabolites, and captopril could be used as potential antiviral drugs against COVID-19. We provide data on the potential covalent interaction of disulfiram and its metabolites with the substrate binding subsite of 3CLpro and propose a possible mechanism for the irreversible protease inactivation thought the reaction of the aforementioned compounds with the Cys145. Although, captopril is shown to be a potential ligand of 3CLpro, it is not recommended anti-COVID-19 therapy, due to the fact that it can induce the expression of the viral cellular receptor such as, angiotensin-converting enzyme ACE-2, and thus, making the patient potentially more susceptible to infection. On the other hand, disulfiram, an alcoholism-averting drug, has been previously proposed as an antimicrobial and anti-SARS and MERS agent, safe to use even at higher doses with low side effects, it is recommended to be tested for control of SARS-CoV-2 infection.Communicated by Ramaswamy H. Sarma.