Unveiling potential inhibitors targeting the nucleocapsid protein of SARS-CoV-2: Structural insights into their binding sites.

The Nucleocapsid (N) protein of SARS-CoV-2 plays a crucial role in viral replication and pathogenesis, making it an attractive target for developing antiviral therapeutics. In this study, we used differential scanning fluorimetry to establish a high-throughput screening method for identifying high-affinity ligands of N-terminal domain of the N protein (N-NTD). We screened an FDA-approved drug library of 1813 compounds and identified 102 compounds interacting with N-NTD. The screened compounds were further investigated for their ability to inhibit the nucleic-acid binding activity of the N protein using electrophoretic mobility-shift assays. We have identified three inhibitors, Ceftazidime, Sennoside A, and Tannic acid, that disrupt the N protein's interaction with RNA probe. Ceftazidime and Sennoside A exhibited nano-molar range binding affinities with N protein, determined through surface plasmon resonance. The binding sites of Ceftazidime and Sennoside A were investigated using [1H, 15N]-heteronuclear single quantum coherence (HSQC) NMR spectroscopy. Ceftazidime and Sennoside A bind to the putative RNA binding site of the N protein, thus providing insights into the inhibitory mechanism of these compounds. These findings will contribute to the development of novel antiviral agents targeting the N protein of SARS-CoV-2.

Targeting sgRNA N secondary structure as a way of inhibiting SARS-CoV-2 replication.

SARS-CoV-2 is a betacoronavirus that causes COVID-19, a global pandemic that has resulted in many infections, deaths, and socio-economic challenges. The virus has a large positive-sense, single-stranded RNA genome of ∼30 kb, which produces subgenomic RNAs (sgRNAs) through discontinuous transcription. The most abundant sgRNA is sgRNA N, which encodes the nucleocapsid (N) protein. In this study, we probed the secondary structure of sgRNA N and a shorter model without a 3' UTR in vitro, using the SHAPE (selective 2'-hydroxyl acylation analyzed by a primer extension) method and chemical mapping with dimethyl sulfate and 1-cyclohexyl-(2-morpholinoethyl) carbodiimide metho-p-toluene sulfonate. We revealed the secondary structure of sgRNA N and its shorter variant for the first time and compared them with the genomic RNA N structure. Based on the structural information, we designed gapmers, siRNAs and antisense oligonucleotides (ASOs) to target the N protein coding region of sgRNA N. We also generated eukaryotic expression vectors containing the complete sequence of sgRNA N and used them to screen for new SARS-CoV-2 gene N expression inhibitors. Our study provides novel insights into the structure and function of sgRNA N and potential therapeutic tools against SARS-CoV-2.

A hybrid structure determination approach to investigate the druggability of the nucleocapsid protein of SARS-CoV-2.

The pandemic caused by SARS-CoV-2 has called for concerted efforts to generate new insights into the biology of betacoronaviruses to inform drug screening and development. Here, we establish a workflow to determine the RNA recognition and druggability of the nucleocapsid N-protein of SARS-CoV-2, a highly abundant protein crucial for the viral life cycle. We use a synergistic method that combines NMR spectroscopy and protein-RNA cross-linking coupled to mass spectrometry to quickly determine the RNA binding of two RNA recognition domains of the N-protein. Finally, we explore the druggability of these domains by performing an NMR fragment screening. This workflow identified small molecule chemotypes that bind to RNA binding interfaces and that have promising properties for further fragment expansion and drug development.

Folic acid: a potential inhibitor against SARS-CoV-2 nucleocapsid protein.

CONTEXT: Coronavirus disease 2019 is a global pandemic. Studies suggest that folic acid has antiviral effects. Molecular docking shown that folic acid can act on SARS-CoV-2 Nucleocapsid Phosphoprotein (SARS-CoV-2 N). OBJECTIVE: To identify novel molecular therapeutic targets for SARS-CoV-2. MATERIALS AND METHODS: Traditional Chinese medicine targets and virus-related genes were identified with network pharmacology and big data analysis. Folic acid was singled out by molecular docking, and its potential target SARS-CoV-2 N was identified. Inhibition of SARS-CoV-2 N of folic acid was verified at the cellular level. RESULTS: In total, 8355 drug targets were potentially involved in the inhibition of SARS-CoV-2. 113 hub genes were screened by further association analysis between targets and virus-related genes. The hub genes related compounds were analysed and folic acid was screened as a potential new drug. Moreover, molecular docking showed folic acid could target on SARS-CoV-2 N which inhibits host RNA interference (RNAi). Therefore, this study was based on RNAi to verify whether folic acid antagonises SARS-CoV-2 N. Cell-based experiments shown that RNAi decreased mCherry expression by 81.7% (p < 0.001). This effect was decreased by 8.0% in the presence of SARS-CoV-2 N, indicating that SARS-CoV-2 N inhibits RNAi. With increasing of folic acid concentration, mCherry expression decreased, indicating that folic acid antagonises the regulatory effect of SARS-CoV-2 N on host RNAi. DISCUSSION AND CONCLUSIONS: Folic acid may be an antagonist of SARS-CoV-2 N, but its effect on viruses unclear. In future, the mechanisms of action of folic acid against SARS-CoV-2 N should be studied.

Computational guided identification of novel potent inhibitors of N-terminal domain of nucleocapsid protein of severe acute respiratory syndrome coronavirus 2.

The Coronavirus Disease 2019, caused by the severe acute respiratory syndrome coronavirus 2 is an exceptionally contagious disease that leads to global epidemics with elevated mortality and morbidity. There are currently no efficacious drugs targeting coronavirus disease 2019, therefore, it is an urgent requirement for the development of drugs to control this emerging disease. Owing to the importance of nucleocapsid protein, the present study focuses on targeting the N-terminal domain of nucleocapsid protein from severe acute respiratory syndrome coronavirus 2 to identify the potential compounds by computational approaches such as pharmacophore modeling, virtual screening, docking and molecular dynamics. We found three molecules (ZINC000257324845, ZINC000005169973 and ZINC000009913056), which adopted a similar conformation as guanosine monophosphate (GMP) within the N-terminal domain active site and exhibiting high binding affinity (>-8.0 kcalmol-1). All the identified compounds were stabilized by hydrogen bonding with Arg107, Tyr111 and Arg149 of N-terminal domain. Additionally, the aromatic ring of lead molecules formed π interactions with Tyr109 of N-terminal domain. Molecular dynamics and Molecular mechanic/Poisson-Boltzmann surface area results revealed that N-terminal domain - ligand(s) complexes are less dynamic and more stable than N-terminal domain - GMP complex. As the identified compounds share the same corresponding pharmacophore properties, therefore, the present results may serve as a potential lead for the development of inhibitors against severe acute respiratory syndrome coronavirus 2. Communicated by Ramaswamy H. Sarma.

Virtual screening of phytoconstituents from miracle herb nigella sativa targeting nucleocapsid protein and papain-like protease of SARS-CoV-2 for COVID-19 treatment.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel etiological agent of coronavirus disease 2019 (COVID-19). Nigella sativa, commonly known as black seed or black cumin, has been a historical and traditional plant since thousands of years. Based on their therapeutic efficacy, the chief components of terpenoids and flavonoids were selected from N. sativa seeds and seed oil. This study was designed to check the antiviral efficacy of N. sativa main phytoconstituents against five potential targets of SARS-CoV-2 using in silico structure-based virtual screening approach. Out of twenty five phytocomponents, ten components showed best binding affinity against two viral proteins viz. N-terminal RNA binding domain (NRBD; PDB ID: 6M3M) of nucleocapsid protein and papain-like protease (PL-PRO; PDB ID: 6W9C) of SARS-CoV-2 using AutoDock 4.2.6, AutoDock Vina and iGEMDOCK. PASS analyses of all ten phytocomponents using Lipinski's Rule of five showed promising results. Further, druglikeness and toxicity assessment using OSIRIS Data Warrior v5.2.1 software exhibited the feasibility of phytocomponents as drug candidates with no predicted toxicity. Molecular dynamics simulation study of NRBD of SARS-CoV-2 nucleocapsid protein-alpha-spinasterol complex and PL-PRO-cycloeucalenol complex displayed strong stability at 300 K. Both these complexes exhibited constant root mean square deviation (RMSDs) of protein side chains and Cα atoms throughout the simulation run time. Interestingly, PL-PRO and NRBD are key proteins in viral replication, host cell immune evasion and viral assembly. Thus, NRBD and PL-PRO have the potential to serve as therapeutic targets for N. sativa phytoconstituents in drug discovery process against COVID-19.

Small molecule stabilization of non-native protein-protein interactions of SARS-CoV-2 N protein as a mechanism of action against COVID-19.

The outbreak of COVID-19, the disease caused by SARS-CoV-2, continues to affect millions of people around the world. The absence of a globally distributed effective treatment makes the exploration of new mechanisms of action a key step to address this situation. Stabilization of non-native Protein-Protein Interactions (PPIs) of the nucleocapsid protein of MERS-CoV has been reported as a valid strategy to inhibit viral replication. In this study, the applicability of this unexplored mechanism of action against SARS-CoV-2 is analyzed. During our research, we were able to find three inducible interfaces of SARS-CoV-2 N protein NTD, compare them to the previously reported MERS-CoV stabilized dimers, and identify those residues that are responsible for their formation. A drug discovery protocol implemented consisting of docking, molecular dynamics and MM-GBSA enabled us to find several compounds that might be able to exploit this mechanism of action. In addition, a common catechin skeleton was found among many of these molecules, which might be useful for further drug design. We consider that our findings could motivate future research in the fields of drug discovery and design towards the exploitation of this previously unexplored mechanism of action against COVID-19.Communicated by Ramaswamy H. Sarma.

Novel nucleocapsid protein-targeting phenanthridine inhibitors of SARS-CoV-2.

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is unprecedented in human history. As a major structural protein, nucleocapsid protein (NPro) is critical to the replication of SARS-CoV-2. In this work, 17 NPro-targeting phenanthridine derivatives were rationally designed and synthesized, based on the crystal structure of NPro. Most of these compounds can interact with SARS-CoV-2 NPro tightly and inhibit the replication of SARS-CoV-2 in vitro. Compounds 12 and 16 exhibited the most potent anti-viral activities with 50% effective concentration values of 3.69 and 2.18 µM, respectively. Furthermore, site-directed mutagenesis of NPro and Surface Plasmon Resonance (SPR) assays revealed that 12 and 16 target N-terminal domain (NTD) of NPro by binding to Tyr109. This work found two potent anti-SARS-CoV-2 bioactive compounds and also indicated that SARS-CoV-2 NPro-NTD can be a target for new anti-virus agents.

Promising Antiviral Activities of Natural Flavonoids against SARS-CoV-2 Targets: Systematic Review.

The ongoing COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) became a globally leading public health concern over the past two years. Despite the development and administration of multiple vaccines, the mutation of newer strains and challenges to universal immunity has shifted the focus to the lack of efficacious drugs for therapeutic intervention for the disease. As with SARS-CoV, MERS-CoV, and other non-respiratory viruses, flavonoids present themselves as a promising therapeutic intervention given their success in silico, in vitro, in vivo, and more recently, in clinical studies. This review focuses on data from in vitro studies analyzing the effects of flavonoids on various key SARS-CoV-2 targets and presents an analysis of the structure-activity relationships for the same. From 27 primary papers, over 69 flavonoids were investigated for their activities against various SARS-CoV-2 targets, ranging from the promising 3C-like protease (3CLpro) to the less explored nucleocapsid (N) protein; the most promising were quercetin and myricetin derivatives, baicalein, baicalin, EGCG, and tannic acid. We further review promising in silico studies featuring activities of flavonoids against SARS-CoV-2 and list ongoing clinical studies involving the therapeutic potential of flavonoid-rich extracts in combination with synthetic drugs or other polyphenols and suggest prospects for the future of flavonoids against SARS-CoV-2.

Antiviral Activity of Metabolites from Peruvian Plants against SARS-CoV-2: An In Silico Approach.

(1) Background: The COVID-19 pandemic lacks treatments; for this reason, the search for potential compounds against therapeutic targets is still necessary. Bioinformatics tools have allowed the rapid in silico screening of possible new metabolite candidates from natural resources or repurposing known ones. Thus, in this work, we aimed to select phytochemical candidates from Peruvian plants with antiviral potential against three therapeutical targets of SARS-CoV-2. (2) Methods: We applied in silico technics, such as virtual screening, molecular docking, molecular dynamics simulation, and MM/GBSA estimation. (3) Results: Rutin, a compound present in Peruvian native plants, showed affinity against three targets of SARS-CoV-2. The molecular dynamics simulation demonstrated the high stability of receptor-ligand systems during the time of the simulation. Our results showed that the Mpro-Rutin system exhibited higher binding free energy than PLpro-Rutin and N-Rutin systems through MM/GBSA analysis. (4) Conclusions: Our study provides insight on natural metabolites from Peruvian plants with therapeutical potential. We found Rutin as a potential candidate with multiple pharmacological properties against SARS-CoV-2.

Coronavirus Porcine Epidemic Diarrhea Virus Nucleocapsid Protein Interacts with p53 To Induce Cell Cycle Arrest in S-Phase and Promotes Viral Replication.

Subversion of the host cell cycle to facilitate viral replication is a common feature of coronavirus infections. Coronavirus nucleocapsid (N) protein can modulate the host cell cycle, but the mechanistic details remain largely unknown. Here, we investigated the effects of manipulation of porcine epidemic diarrhea virus (PEDV) N protein on the cell cycle and the influence on viral replication. Results indicated that PEDV N induced Vero E6 cell cycle arrest at S-phase, which promoted viral replication (P < 0.05). S-phase arrest was dependent on the N protein nuclear localization signal S71NWHFYYLGTGPHADLRYRT90 and the interaction between N protein and p53. In the nucleus, the binding of N protein to p53 maintained consistently high-level expression of p53, which activated the p53-DREAM pathway. The key domain of the N protein interacting with p53 was revealed to be S171RGNSQNRGNNQGRGASQNRGGNN194 (NS171-N194), in which G183RG185 are core residues. NS171-N194 and G183RG185 were essential for N-induced S-phase arrest. Moreover, small molecular drugs targeting the NS171-N194 domain of the PEDV N protein were screened through molecular docking. Hyperoside could antagonize N protein-induced S-phase arrest by interfering with interaction between N protein and p53 and inhibit viral replication (P < 0.05). The above-described experiments were also validated in porcine intestinal cells, and data were in line with results in Vero E6 cells. Therefore, these results reveal the PEDV N protein interacts with p53 to activate the p53-DREAM pathway, and subsequently induces S-phase arrest to create a favorable environment for virus replication. These findings provide new insight into the PEDV-host interaction and the design of novel antiviral strategies against PEDV. IMPORTANCE Many viruses subvert the host cell cycle to create a cellular environment that promotes viral growth. PEDV, an emerging and reemerging coronavirus, has led to substantial economic loss in the global swine industry. Our study is the first to demonstrate that PEDV N-induced cell cycle arrest during the S-phase promotes viral replication. We identified a novel mechanism of PEDV N-induced S-phase arrest, where the binding of PEDV N protein to p53 maintains consistently high levels of p53 expression in the nucleus to mediate S-phase arrest by activating the p53-DREAM pathway. Furthermore, a small molecular compound, hyperoside, targeted the PEDV N protein, interfering with the interaction between the N protein and p53 and, importantly, inhibited PEDV replication by antagonizing cell cycle arrest. This study reveals a new mechanism of PEDV-host interaction and also provides a novel antiviral strategy for PEDV. These data provide a foundation for further research into coronavirus-host interactions.

Repurposing Ivermectin for COVID-19: Molecular Aspects and Therapeutic Possibilities.

As of January 2021, SARS-CoV-2 has killed over 2 million individuals across the world. As such, there is an urgent need for vaccines and therapeutics to reduce the burden of COVID-19. Several vaccines, including mRNA, vector-based vaccines, and inactivated vaccines, have been approved for emergency use in various countries. However, the slow roll-out of vaccines and insufficient global supply remains a challenge to turn the tide of the pandemic. Moreover, vaccines are important tools for preventing the disease but therapeutic tools to treat patients are also needed. As such, since the beginning of the pandemic, repurposed FDA-approved drugs have been sought as potential therapeutic options for COVID-19 due to their known safety profiles and potential anti-viral effects. One of these drugs is ivermectin (IVM), an antiparasitic drug created in the 1970s. IVM later exerted antiviral activity against various viruses including SARS-CoV-2. In this review, we delineate the story of how this antiparasitic drug was eventually identified as a potential treatment option for COVID-19. We review SARS-CoV-2 lifecycle, the role of the nucleocapsid protein, the turning points in past research that provided initial 'hints' for IVM's antiviral activity and its molecular mechanism of action- and finally, we culminate with the current clinical findings.

Targeting the Complement Serine Protease MASP-2 as a Therapeutic Strategy for Coronavirus Infections.

MASP-2, mannose-binding protein-associated serine protease 2, is a key enzyme in the lectin pathway of complement activation. Hyperactivation of this protein by human coronaviruses SARS-CoV, MERS-CoV and SARS-CoV-2 has been found to contribute to aberrant complement activation in patients, leading to aggravated lung injury with potentially fatal consequences. This hyperactivation is triggered in the lungs through a conserved, direct interaction between MASP-2 and coronavirus nucleocapsid (N) proteins. Blocking this interaction with monoclonal antibodies and interfering directly with the catalytic activity of MASP-2, have been found to alleviate coronavirus-induced lung injury both in vitro and in vivo. In this study, a virtual library of 8736 licensed drugs and clinical agents has been screened in silico according to two parallel strategies. The first strategy aims at identifying direct inhibitors of MASP-2 catalytic activity, while the second strategy focusses on finding protein-protein interaction inhibitors (PPIs) of MASP-2 and coronaviral N proteins. Such agents could represent promising support treatment options to prevent lung injury and reduce mortality rates of infections caused by both present and future-emerging coronaviruses. Forty-six drug repurposing candidates were purchased and, for the ones selected as potential direct inhibitors of MASP-2, a preliminary in vitro assay was conducted to assess their interference with the lectin pathway of complement activation. Some of the tested agents displayed a dose-response inhibitory activity of the lectin pathway, potentially providing the basis for a viable support strategy to prevent the severe complications of coronavirus infections.

The nucleocapsid protein of zoonotic betacoronaviruses is an attractive target for antiviral drug discovery.

Betacoronaviruses are in one genera of coronaviruses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome-related coronavirus (MERS-CoV), etc. These viruses threaten public health and cause dramatic economic losses. The nucleocapsid (N) protein is a structural protein of betacoronaviruses with multiple functions such as forming viral capsids with viral RNA, interacting with viral membrane protein to form the virus core with RNA, binding to several cellular kinases for signal transductions, etc. In this review, we highlighted the potential of the N protein as a suitable antiviral target from different perspectives, including structure, functions, and antiviral strategies for combatting betacoronaviruses.

Nucleocapsid protein of SARS-CoV-2 phase separates into RNA-rich polymerase-containing condensates.

The etiologic agent of the Covid-19 pandemic is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The viral membrane of SARS-CoV-2 surrounds a helical nucleocapsid in which the viral genome is encapsulated by the nucleocapsid protein. The nucleocapsid protein of SARS-CoV-2 is produced at high levels within infected cells, enhances the efficiency of viral RNA transcription, and is essential for viral replication. Here, we show that RNA induces cooperative liquid-liquid phase separation of the SARS-CoV-2 nucleocapsid protein. In agreement with its ability to phase separate in vitro, we show that the protein associates in cells with stress granules, cytoplasmic RNA/protein granules that form through liquid-liquid phase separation and are modulated by viruses to maximize replication efficiency. Liquid-liquid phase separation generates high-density protein/RNA condensates that recruit the RNA-dependent RNA polymerase complex of SARS-CoV-2 providing a mechanism for efficient transcription of viral RNA. Inhibition of RNA-induced phase separation of the nucleocapsid protein by small molecules or biologics thus can interfere with a key step in the SARS-CoV-2 replication cycle.

An Overview of the Crystallized Structures of the SARS-CoV-2.

Many research teams all over the world focus their research on the SARS-CoV-2, the new coronavirus that causes the so-called COVID-19 disease. Most of the studies identify the main protease or 3C-like protease (Mpro/3CLpro) as a valid target for large-spectrum inhibitors. Also, the interaction of the human receptor angiotensin-converting enzyme 2 (ACE2) with the viral surface glycoprotein (S) is studied in depth. Structural studies tried to identify the residues responsible for enhancement/weaken virus-ACE2 interactions or the cross-reactivity of the neutralizing antibodies. Although the understanding of the immune system and the hyper-inflammatory process in COVID-19 are crucial for managing the immediate and the long-term consequences of the disease, not many X-ray/NMR/cryo-EM crystals are available. In addition to 3CLpro, the crystal structures of other nonstructural proteins offer valuable information for elucidating some aspects of the SARS-CoV-2 infection. Thus, the structural analysis of the SARS-CoV-2 is currently mainly focused on three directions-finding Mpro/3CLpro inhibitors, the virus-host cell invasion, and the virus-neutralizing antibody interaction.

Repurposing of SARS-CoV nucleocapsid protein specific nuclease resistant RNA aptamer for therapeutics against SARS-CoV-2.

COVID-19 pandemic is rapidly advancing among human population. Development of new interventions including therapeutics and vaccines against SARS-CoV-2 will require time and validation before it could be made available for public use. Keeping in view of the emergent and evolving situation the motive is to repurpose and test the immediate efficacy of available drugs and therapeutics against COVID-19. Through this article we propose and discuss the possibility of repurposing the available nuclease resistant RNA aptamer against the nucleocapsid protein of SARS-CoV as a potential therapeutic agent for COVID-19.