Structural differences in 3C-like protease (Mpro) from SARS-CoV and SARS-CoV-2: molecular insights revealed by Molecular Dynamics Simulations

Investigating the mechanisms of ethanol-induced disruption of COVID-19 lipid bilayers through molecular dynamics simulations

CONTEXT

The COVID-19 pandemic, caused by the SARS-CoV-2 coronavirus, began in December 2019 in Wuhan, China. To mitigate the spread of COVID-19, public health officials strongly recommended preventive measures such as disinfectants, alcohol-based hand sanitizers, and face masks. The effect of ethanol on virus structure and inactivation remains unclear, and its molecular mechanism needs to be elucidated. This study elucidates how ethanol solutions interact with the lipid bilayer of the COVID-19 virus utilizing molecular dynamics (MD) simulations. Its findings indicated that ethanol can deactivate the virus through two primary mechanisms. First, when ethanol penetrates the viral membrane, it disrupts the structural integrity of the lipid bilayer, leading to membrane disruption. This alteration in morphology is critical as it compromises the virus's ability to maintain its structure and function.

METHODS

For the simulation, a lipid bilayer containing the spike protein of SARS-CoV-2 was constructed. The interaction between the viral membrane and ethanol solution was then simulated using GROMACS 5.1.4 for molecular dynamics (MD) analysis. Also, visual molecular dynamics (VMD1.9.3) was used for visualization. The study calculated the Lennard-Jones (LJ) and electrostatic interactions between ethanol and the lipid bilayer, and it analyzed the conformational changes in the spike protein following ethanol adsorption. Additionally, the effects of ethanol penetration on the morphology of the lipid bilayer were evaluated.

Biochemical Screening of Phytochemicals and Identification of Scopoletin as a Potential Inhibitor of SARS-CoV-2 Mpro, Revealing Its Biophysical Impact on Structural Stability

The main protease (Mpro or 3CLpro or nsp5) of SARS-CoV-2 is crucial to the life cycle and pathogenesis of SARS-CoV-2, making it an attractive drug target to develop antivirals. This study employed the virtual screening of a few phytochemicals, and the resultant best compound, Scopoletin, was further investigated by a FRET-based enzymatic assay, revealing an experimental IC50 of 15.75 µM. The impact of Scopoletin on Mpro was further investigated by biophysical and MD simulation studies. Fluorescence spectroscopy identified a strong binding constant of 3.17 × 104 M⁻1 for Scopoletin binding to Mpro, as demonstrated by its effective fluorescence quenching of Mpro. Additionally, CD spectroscopy showed a significant reduction in the helical content of Mpro upon interaction with Scopoletin. The findings of thermodynamic measurements using isothermal titration calorimetry (ITC) supported the spectroscopic data, indicating a tight binding of Scopoletin to Mpro with a KA of 2.36 × 103 M-1. Similarly, interaction studies have also revealed that Scopoletin forms hydrogen bonds with the amino acids nearest to the active site, and this has been further supported by molecular dynamics simulation studies. These findings indicate that Scopoletin may be developed as a potential antiviral treatment for SARS-CoV-2 by targeting Mpro.

Alpha-helices as alignment reporters in residual dipolar coupling analysis of proteins

Inclusion of residual dipolar couplings (RDCs) during the early rounds of protein structure determination requires use of a floating alignment tensor or knowledge of the alignment tensor strength and rhombicity. For proteins with interdomain motion, such analysis can falsely hide the presence of domain dynamics. We demonstrate for three proteins, maltotriose-ligated maltose binding protein (MBP), Ca2+-ligated calmodulin, and a monomeric N-terminal deletion mutant of the SARS-CoV-2 Main Protease, MPro, that good alignment tensor estimates of their domains can be obtained from RDCs measured for residues that are identified as α-helical based on their chemical shifts. The program, Helix-Fit, fits the RDCs to idealized α-helical coordinates, often yielding a comparable or better alignment tensor estimate than fitting to the actual high-resolution X-ray helix coordinates. The 13 helices of ligated MBP all show very similar alignment tensors, indicative of a high degree of order relative to one another. By contrast, while for monomeric MPro the alignment strengths of the five helices in the C-terminal helical domain (residues 200-306) are very similar, pointing to a well-ordered domain, the single α-helix Y54-I59 in the N-terminal catalytic domain (residues 10-185) aligns considerably weaker. This result indicates the presence of large amplitude motions of either Y54-I59 or of the entire N-terminal domain relative to the C-terminal domain, contrasting with the high degree of order seen in the native homodimeric structure.

Identification of promising SARS-CoV-2 main protease inhibitor through molecular docking, dynamics simulation, and ADMET analysis

The COVID-19 pandemic caused by SARS-CoV-2 continues to pose a major challenge to global health. Targeting the main protease of the virus (Mpro), which is essential for viral replication and transcription, offers a promising approach for therapeutic intervention. In this study, advanced computational techniques such as molecular docking and molecular dynamics simulations were used to screen a series of antiviral compounds for their potential inhibitory effect on the SARS-CoV-2 Mpro. A comprehensive analysis of compounds from the ChemDiv and PubChem databases was performed. The physicochemical properties, pharmacokinetics, and ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) profiles were evaluated to determine drug similarity and safety. Compound 4896 - 4038 proved to be the most promising candidate. It exhibited a favorable balance between molecular weight (491.06) and lipophilicity (logP 3.957), high intestinal absorption (92.119%), and broad tissue distribution (VDss of 0.529), indicating good oral bioavailability and therapeutic potential. Molecular docking studies showed that 4896 - 4038 has a strong binding affinity to the active site of Mpro and forms key interactions, such as hydrogen bonds, carbon-hydrogen bonds, pi-sulfur, and multiple van der Waals and pi-pi stacked bonds. The binding energy was comparable to that of the reference drug X77, indicating potential efficacy. Molecular dynamics simulations over 300 ns confirmed the stability of the Mpro/4896 - 4038 complex of protein-ligand. Free energy landscape mapping and MM/PBSA calculations further substantiated the favorable binding and stability of the complex. Importantly, 4896 - 4038 exhibited a comparatively favorable safety profile. In summary, compound 4896 - 4038 shows significant potential as a potent SARS-CoV-2 Mpro inhibitor, combining potent inhibitory activity with favorable pharmacokinetic and safety profiles. These results support the further development of 4896 - 4038 as a promising therapeutic agent in the fight against COVID-19 that warrants experimental validation and clinical investigation.

Time-resolved fluorescence studies reveal differences in dynamic motion between main proteases of SARS-CoV-2 and SARS-CoV

The main protease (Mpro) is an attractive drug target for inhibiting the coronavirus. Lots of research has focused on the static viewpoint of the Mpro, such as the X-ray crystal structure, inhibitors design, and the transition between monomer and dimer. However, the attention to the dynamical features of Mpro is limited, which is essential for a deeper determination of the properties of the target protein. In our research, we constructed three single-tryptophan mutants (W31IN, W207IN, and W218IN) of Mpro from SARS-CoV-2 and SARS-CoV to monitor the motion of Mpro at the nano-second timescale using the time-resolved fluorescence assay. We found that the temperature-dependent Stokes shift results show various behaviors among the three single-tryptophan mutants: the microenvironment around the Trp207 residue is more temperature-sensitive compared to that in residues Trp31 and Trp218. The molecular dynamic simulation results further support that MproSARS is more flexible than that of MproSARS2. This difference is directly related to the distinct perturbations of residues Phe185 to Gln192, a loop that connects domain II and domain III. For the first time, we were able to reveal the different motions between MproSARS2 and MproSARS, although the static structures of these two are not distinguished. The differences in dynamics would be an essential step towards understanding the evolving trend of coronavirus, providing a comprehensive view of the properties of Mpro, and offering perspectives for designing inhibitors for further research.

Revealing SARS-CoV-2 Mpro mutation cold and hot spots: Dynamic residue network analysis meets machine learning

Deciphering the effect of evolutionary mutations of viruses and predicting future mutations is crucial for designing long-lasting and effective drugs. While understanding the impact of current mutations on protein drug targets is feasible, predicting future mutations due to natural evolution of viruses and environmental pressures remains challenging. Here, we leveraged existing mutation data during the evolution of the SARS-CoV-2 protein drug target main protease (Mpro) to test the predictive power of dynamic residue network (DRN) analysis in identifying mutation cold and hot spots. We conducted molecular dynamics simulations on the Mpro of SARS-CoV-2 (Wuhan strain) and calculated eight DRN metrics (averaged BC, CC, DC, EC, ECC, KC, L, PR), each of which identifies a unique network feature within the protein. The sets of residues with the highest and lowest values for each metric, comprising potential cold and hot spots, were compared to published biochemical analyses and per residue mutation frequencies observed across five SARS-CoV-2 lineages, encompassing a total of 191,878 sequences. Individual DRN metrics displayed only modest power to predict the mutation frequency of individual residues. However, integrating the eight DRN metrics with additional structural and sequence-derived metrics allowed us to develop machine learning models which significantly improved the prediction of residue mutation frequency. While further refinements should enhance accuracy, we demonstrated a robust method to understand pathogen evolution. This approach can also guide the development of long-lasting drugs by targeting functional residues located in and near active site, and allosteric sites, that are less prone to mutations.

Theoretical insights into the binding interaction of Nirmatrelvir with SARS-CoV-2 Mpro mutants (C145A and C145S): MD simulations and binding free-energy calculation to understand drug resistance

Mpro, the main protease and a crucial enzyme in SARS-CoV-2 is the most fascinating molecular target for pharmacological treatment and is also liable for viral protein maturation. For antiviral therapy, no drugs have been approved clinically to date. Targeting the Mpro with a compound having inhibitory properties against it can hinder viral replication. The therapeutic potential of the antiviral compound Nirmatrelvir (NMV) against SARS-CoV-2 Mpro was investigated using a systematic approach of molecular docking, MD simulations, and binding free energy calculation based on the MM-GBSA method. NMV, a covalent inhibitor with a recently revealed chemical structure, is a promising oral antiviral clinical candidate with significant in vitro anti-SARS-CoV-2 action in third-phase clinical trials. To explore the therapeutic ability and possible drug resistance, the Mpro system was studied for WT and two of its primary mutants (C145A & C145S). The protein-ligand (Mpro/NMV) complexes were further examined through long MD simulations to check the possible drug resistance in the mutants. To understand the binding affinity, the MM-GBSA method was applied to the Mpro/NMV complexes. Moreover, PCA analysis confirms the detachment of the linker region from the major domains in C145S and C145A mutants allowing for conformational alterations in the active-site region. Based on the predicted biological activities and binding affinities of NMV to WT and mutant (C145A & C145S) Mpro, it can be stipulated that NMV may have conventional potency to act as an anti-viral agent against WT Mpro, while the catalytic-dyad mutations may show substantial mutation-induced drug resistance.Communicated by Ramaswamy H. Sarma.

Nonpeptidic Irreversible Inhibitors of SARS-CoV-2 Main Protease with Potent Antiviral Activity

SARS-CoV-2 infections pose a high risk for vulnerable patients. In this study, we designed benzoic acid halopyridyl esters bearing a variety of substituents as irreversible inhibitors of the main viral protease (Mpro). Altogether, 55 benzoyl chloro/bromo-pyridyl esters were synthesized, with broad variation of the substitution pattern on the benzoyl moiety. A workflow was employed for multiparametric optimization, including Mpro inhibition assays of SARS-CoV-2 and related pathogenic coronaviruses, the duration of enzyme inhibition, the compounds' stability versus glutathione, cytotoxicity, and antiviral activity. Several compounds showed IC50 values in the low nanomolar range, kinact/Ki values of >100,000 M-1 s-1 and high antiviral activity. High-resolution X-ray cocrystal structures indicated an important role of ortho-fluorobenzoyl substitution, forming a water network that stabilizes the inhibitor-bound enzyme. The most potent antiviral compound was the p-ethoxy-o-fluorobenzoyl chloropyridyl ester (PSB-21110, 29b, MW 296 g/mol; EC50 2.68 nM), which may serve as a lead structure for broad-spectrum anticoronaviral therapeutics.

A potential allosteric inhibitor of SARS-CoV-2 main protease (Mpro) identified through metastable state analysis

Anti-COVID19 drugs, such as nirmatrelvir, have been developed targeting the SARS-CoV-2 main protease, Mpro, based on the critical requirement of its proteolytic processing of the viral polyproteins into functional proteins essential for viral replication. However, the emergence of SARS-CoV-2 variants with Mpro mutations has raised the possibility of developing resistance against these drugs, likely due to therapeutic targeting of the Mpro catalytic site. An alternative to these drugs is the development of drugs that target an allosteric site distant from the catalytic site in the protein that may reduce the chance of the emergence of resistant mutants. Here, we combine computational analysis with in vitro assay and report the discovery of a potential allosteric site and an allosteric inhibitor of SARS-CoV-2 Mpro. Specifically, we identified an Mpro metastable state with a deformed catalytic site harboring potential allosteric sites, raising the possibility that stabilization of this metastable state through ligand binding can lead to the inhibition of Mpro activity. We then performed a computational screening of a library (∼4.2 million) of drug-like compounds from the ZINC database and identified several candidate molecules with high predicted binding affinity. MD simulations showed stable binding of the three top-ranking compounds to the putative allosteric sites in the protein. Finally, we tested the three compounds in vitro using a BRET-based Mpro biosensor and found that one of the compounds (ZINC4497834) inhibited the Mpro activity. We envisage that the identification of a potential allosteric inhibitor of Mpro will aid in developing improved anti-COVID-19 therapy.

Peptidomimetics as potent dual SARS-CoV-2 cathepsin-L and main protease inhibitors: In silico design, synthesis and pharmacological characterization

In this paper we present the design, synthesis, and biological evaluation of a new series of peptidomimetics acting as potent anti-SARS-CoV-2 agents. Starting from our previously described Main Protease (MPro) and Papain Like Protease (PLPro) dual inhibitor, CV11, here we disclose its high inhibitory activity against cathepsin L (CTSL) (IC50 = 19.80 ± 4.44 nM), an emerging target in SARS-CoV-2 infection machinery. An in silico design, inspired by the structure of CV11, led to the development of a library of peptidomimetics showing interesting activities against CTSL and Mpro, allowing us to trace the chemical requirements for the binding to both enzymes. The screening in Vero cells infected with 5 different SARS-CoV-2 variants of concerns, highlighted sub-micromolar activities for most of the synthesized compounds (13, 15, 16, 17 and 31) in agreement with the enzymatic inhibition assays results. The compounds showed lack of activity against several different RNA viruses except for the 229E and OC43 human coronavirus strains, also characterized by a cathepsin-L dependent release into the host cells. The most promising derivatives were also evaluated for their chemical and metabolic in-vitro stability, with derivatives 15 and 17 showing a suitable profile for further preclinical characterization.

Unexpected Single-Ligand Occupancy and Negative Cooperativity in the SARS-CoV-2 Main Protease

Many homodimeric enzymes tune their functions by exploiting either negative or positive cooperativity between subunits. In the SARS-CoV-2 Main protease (Mpro) homodimer, the latter has been suggested by symmetry in most of the 500 reported protease/ligand complex structures solved by macromolecular crystallography (MX). Here we apply the latter to both covalent and noncovalent ligands in complex with Mpro. Strikingly, our experiments show that the occupation of both active sites of the dimer originates from an excess of ligands. Indeed, cocrystals obtained using a 1:1 ligand/protomer stoichiometry lead to single occupation only. The empty binding site exhibits a catalytically inactive geometry in solution, as suggested by molecular dynamics simulations. Thus, Mpro operates through negative cooperativity with the asymmetric activity of the catalytic sites. This allows it to function with a wide range of substrate concentrations, making it resistant to saturation and potentially difficult to shut down, all properties advantageous for the virus' adaptability and resistance.

The Main Protease of Middle East Respiratory Syndrome Coronavirus Induces Cleavage of Mitochondrial Antiviral Signaling Protein to Antagonize the Innate Immune Response

Mitochondrial antiviral signaling protein (MAVS) is a crucial signaling adaptor in the sensing of positive-sense RNA viruses and the subsequent induction of the innate immune response. Coronaviruses have evolved multiple mechanisms to evade this response, amongst others, through their main protease (Mpro), which is responsible for the proteolytic cleavage of the largest part of the viral replicase polyproteins pp1a and pp1ab. Additionally, it can cleave cellular substrates, such as innate immune signaling factors, to dampen the immune response. Here, we show that MAVS is cleaved in cells infected with Middle East respiratory syndrome coronavirus (MERS-CoV), but not in cells infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This cleavage was independent of cellular negative feedback mechanisms that regulate MAVS activation. Furthermore, MERS-CoV Mpro expression induced MAVS cleavage upon overexpression and suppressed the activation of the interferon-β (IFN-β) and nuclear factor-κB (NF-κB) response. We conclude that we have uncovered a novel mechanism by which MERS-CoV downregulates the innate immune response, which is not observed among other highly pathogenic coronaviruses.

AI-driven covalent drug design strategies targeting main protease (mpro) against SARS-CoV-2: structural insights and molecular mechanisms

The emergence of new SARS-CoV-2 variants has raised concerns about the effectiveness of COVID-19 vaccines. To address this challenge, small-molecule antivirals have been proposed as a crucial therapeutic option. Among potential targets for anti-COVID-19 therapy, the main protease (Mpro) of SARS-CoV-2 is important due to its essential role in the virus's life cycle and high conservation. The substrate-binding region of the core proteases of various coronaviruses, including SARS-CoV-2, SARS-CoV, and Middle East respiratory syndrome coronavirus (MERS-CoV), could be used for the generation of new protease inhibitors. Various drug discovery methods have employed a diverse range of strategies, targeting both monomeric and dimeric forms, including drug repurposing, integrating virtual screening with high-throughput screening (HTS), and structure-based drug design, each demonstrating varying levels of efficiency. Covalent inhibitors, such as Nirmatrelvir and MG-101, showcase robust and high-affinity binding to Mpro, exhibiting stable interactions confirmed by molecular docking studies. Development of effective antiviral drugs is imperative to address potential pandemic situations. This review explores recent advances in the search for Mpro inhibitors and the application of artificial intelligence (AI) in drug design. AI leverages vast datasets and advanced algorithms to streamline the design and identification of promising Mpro inhibitors. AI-driven drug discovery methods, including molecular docking, predictive modeling, and structure-based drug repurposing, are at the forefront of identifying potential candidates for effective antiviral therapy. In a time when COVID-19 potentially threat global health, the quest for potent antiviral solutions targeting Mpro could be critical for inhibiting the virus.

Development of de-novo coronavirus 3-chymotrypsin-like protease (3CLpro) inhibitors since COVID-19 outbreak: A strategy to tackle challenges of persistent virus infection

Although no longer a public health emergency of international concern, COVID-19 remains a persistent and critical health concern. The development of effective antiviral drugs could serve as the ultimate piece of the puzzle to curbing this global crisis. 3-chymotrypsin-like protease (3CLpro), with its substrate specificity mirroring that of the main picornavirus 3C protease and conserved across various coronaviruses, emerges as an ideal candidate for broad-spectrum antiviral drug development. Moreover, it holds the potential as a reliable contingency option to combat emerging SARS-CoV-2 variants. In this light, the approved drugs, promising candidates, and de-novo small molecule therapeutics targeting 3CLpro since the COVID-19 outbreak in 2020 are discussed. Emphasizing the significance of diverse structural characteristics in inhibitors, be they peptidomimetic or nonpeptidic, with a shared mission to minimize the risk of cross-resistance. Moreover, the authors propose an innovative optimization strategy for 3CLpro reversible covalent PROTACs, optimizing pharmacodynamics and pharmacokinetics to better prepare for potential future viral outbreaks.