Nuclear magnetic resonance structure of the nucleic acid-binding domain of severe acute respiratory syndrome coronavirus nonstructural protein 3

A review on structural, non-structural, and accessory proteins of SARS-CoV-2: Highlighting drug target sites

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, is a highly transmittable and pathogenic human coronavirus that first emerged in China in December 2019. The unprecedented outbreak of SARS-CoV-2 devastated human health within a short time leading to a global public health emergency. A detailed understanding of the viral proteins including their structural characteristics and virulence mechanism on human health is very crucial for developing vaccines and therapeutics. To date, over 1800 structures of non-structural, structural, and accessory proteins of SARS-CoV-2 are determined by cryo-electron microscopy, X-ray crystallography, and NMR spectroscopy. Designing therapeutics to target the viral proteins has several benefits since they could be highly specific against the virus while maintaining minimal detrimental effects on humans. However, for ongoing and future research on SARS-CoV-2, summarizing all the viral proteins and their detailed structural information is crucial. In this review, we compile comprehensive information on viral structural, non-structural, and accessory proteins structures with their binding and catalytic sites, different domain and motifs, and potential drug target sites to assist chemists, biologists, and clinicians finding necessary details for fundamental and therapeutic research.

Modelling the Transitioning of SARS-CoV-2 nsp3 and nsp4 Lumenal Regions towards a More Stable State on Complex Formation

During coronavirus infection, three non-structural proteins, nsp3, nsp4, and nsp6, are of great importance as they induce the formation of double-membrane vesicles where the replication and transcription of viral gRNA takes place, and the interaction of nsp3 and nsp4 lumenal regions triggers membrane pairing. However, their structural states are not well-understood. We investigated the interactions between nsp3 and nsp4 by predicting the structures of their lumenal regions individually and in complex using AlphaFold2 as implemented in ColabFold. The ColabFold prediction accuracy of the nsp3-nsp4 complex was increased compared to nsp3 alone and nsp4 alone. All cysteine residues in both lumenal regions were modelled to be involved in intramolecular disulphide bonds. A linker region in the nsp4 lumenal region emerged as crucial for the interaction, transitioning to a structured state when predicted in complex. The key interactions modelled between nsp3 and nsp4 appeared stable when the transmembrane regions of nsp3 and nsp4 were added to the modelling either alone or together. While molecular dynamics simulations (MD) demonstrated that the proposed model of the nsp3 lumenal region on its own is not stable, key interactions between nsp and nsp4 in the proposed complex model appeared stable after MD. Together, these observations suggest that the interaction is robust to different modelling conditions. Understanding the functional importance of the nsp4 linker region may have implications for the targeting of double membrane vesicle formation in controlling coronavirus infection.

Anti-Saccharomyces cerevisiae antibodies in patients with COVID-19

BACKGROUND AND STUDY AIM

Anti-Saccharomyces cerevisiae antibodies (ASCA) have been described in many autoimmune diseases (AIDs). Coronavirus disease 2019 (COVID-19) could trigger AIDs. This study aimed to determine the frequency of ASCA in patients with COVID-19.

PATIENTS AND METHODS

This study included 88 adult patients with severe COVID-19, 51 mild COVID-19, and 160 healthy blood donors. ASCA of isotype immunoglobulin (Ig)G and IgA were detected by enzyme-linked immunosorbent assay.

RESULTS

The frequency of ASCA (IgG or IgA) was significantly higher in patients with severe COVID-19 (21.6 % vs 3.7 %, p < 10^-3) and in patients with mild COVID-19 than in the healthy controls (13.7 % vs 3.7 %, p = 0.03). ASCA-IgA was significantly more frequent in patients with severe COVID-19 than in healthy controls (15.9 % vs 0.6 %, p < 10^-3). ASCA-IgG was significantly more frequent in patients with mild COVID-19 than in healthy controls (13.7 % vs 3.1 %, p = 0.02). ASCA (IgG or IgA) were more frequent in severe than in mild COVID-19, but the difference was not statistically significant (21.6 % vs 13.7 %). ASCA-IgA was significantly more frequent in patients with severe than those with mild COVID-19 (15.9 % vs 0 %, p = 0.003). The mean ASCA-IgG and ASCA-IgA levels were significantly higher in patients with severe COVID-19 than in healthy controls (5.8 U/mL ± 11.8 vs 2.3 U/mL ± 2.8, p < 10^-3 and 9.2 U/mL ± 21.5 vs 3.4 U/mL ± 1.7, respectively, p < 10^-3). The mean ASCA-IgG levels were significantly higher in patients with mild COVID-19 than in healthy controls (6.2 U/mL ± 12.9 vs 2.3 U/mL ± 2.8, p < 10^-3). The mean ASCA-IgA levels were significantly higher in patients with severe than in those with mild COVID-19 (9.2 U/mL ± 21.5 vs 2.6 U/mL ± 1.2, p = 0.03).

CONCLUSION

ASCA was more frequent in patients with COVID-19 than in healthy controls.

Two Years into the COVID-19 Pandemic: Lessons Learned

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible and virulent human-infecting coronavirus that emerged in late December 2019 in Wuhan, China, causing a respiratory disease called coronavirus disease 2019 (COVID-19), which has massively impacted global public health and caused widespread disruption to daily life. The crisis caused by COVID-19 has mobilized scientists and public health authorities across the world to rapidly improve our knowledge about this devastating disease, shedding light on its management and control, and spawned the development of new countermeasures. Here we provide an overview of the state of the art of knowledge gained in the last 2 years about the virus and COVID-19, including its origin and natural reservoir hosts, viral etiology, epidemiology, modes of transmission, clinical manifestations, pathophysiology, diagnosis, treatment, prevention, emerging variants, and vaccines, highlighting important differences from previously known highly pathogenic coronaviruses. We also discuss selected key discoveries from each topic and underline the gaps of knowledge for future investigations.

A Mouse-Adapted Model of HCoV-OC43 and Its Usage to the Evaluation of Antiviral Drugs

The human coronavirus OC43 (HCoV-OC43) is one of the most common causes of common cold but can lead to fatal pneumonia in children and elderly. However, the available animal models of HCoV-OC43 did not show respiratory symptoms that are insufficient to assist in screening antiviral agents for respiratory diseases. In this study, we adapted the HCoV-OC43 VR-1558 strain by serial passage in suckling C57BL/6 mice and the resulting mouse-adapted virus at passage 9 (P9) contained 8 coding mutations in polyprotein 1ab, spike (S) protein, and nucleocapsid (N) protein. Pups infected with the P9 virus significantly lost body weight and died within 5 dpi. In cerebral and pulmonary tissues, the P9 virus replication induced the production of G-CSF, IFN-γ, IL-6, CXCL1, MCP-1, MIP-1α, RANTES, IP-10, MIP-1β, and TNF-α, as well as pathological alterations including reduction of neuronal cells and typical symptoms of viral pneumonia. We found that the treatment of arbidol hydrochloride (ARB) or Qingwenjiere Mixture (QJM) efficiently improved the symptoms and decreased n gene expression, inflammatory response, and pathological changes. Furthermore, treating with QJM or ARB raised the P9-infected mice’s survival rate within a 15 day observation period. These findings suggested that the new mouse-adapted HCoV-OC43 model is applicable and reproducible for antiviral studies of HCoV-OC43.

Translational Control of COVID-19 and Its Therapeutic Implication

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of COVID-19, which has broken out worldwide for more than two years. However, due to limited treatment, new cases of infection are still rising. Therefore, there is an urgent need to understand the basic molecular biology of SARS-CoV-2 to control this virus. SARS-CoV-2 replication and spread depend on the recruitment of host ribosomes to translate viral messenger RNA (mRNA). To ensure the translation of their own mRNAs, the SARS-CoV-2 has developed multiple strategies to globally inhibit the translation of host mRNAs and block the cellular innate immune response. This review provides a comprehensive picture of recent advancements in our understanding of the molecular basis and complexity of SARS-CoV-2 protein translation. Specifically, we summarize how this viral infection inhibits host mRNA translation to better utilize translation elements for translation of its own mRNA. Finally, we discuss the potential of translational components as targets for therapeutic interventions.

In silico analysis of SARS-CoV-2 proteins as targets for clinically available drugs

The ongoing pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) requires treatments with rapid clinical translatability. Here we develop a multi-target and multi-ligand virtual screening method to identify FDA-approved drugs with potential activity against SARS-CoV-2 at traditional and understudied viral targets. 1,268 FDA-approved small molecule drugs were docked to 47 putative binding sites across 23 SARS-CoV-2 proteins. We compared drugs between binding sites and filtered out compounds that had no reported activity in an in vitro screen against SARS-CoV-2 infection of human liver (Huh-7) cells. This identified 17 "high-confidence", and 97 "medium-confidence" drug-site pairs. The "high-confidence" group was subjected to molecular dynamics simulations to yield six compounds with stable binding poses at their optimal target proteins. Three drugs-amprenavir, levomefolic acid, and calcipotriol-were predicted to bind to 3 different sites on the spike protein, domperidone to the Mac1 domain of the non-structural protein (Nsp) 3, avanafil to Nsp15, and nintedanib to the nucleocapsid protein involved in packaging the viral RNA. Our "two-way" virtual docking screen also provides a framework to prioritize drugs for testing in future emergencies requiring rapidly available clinical drugs and/or treating diseases where a moderate number of targets are known.

Discovery of compounds inhibiting SARS-COV-2 multi-targets

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a pandemic that has devastated the lives of millions. Researchers around the world are relentlessly working in hopes of finding a cure. Even though the virus shares similarities with reported SARS-CoV and MERS-CoV at the genomic and proteomic level, efforts to repurpose already known drugs against SARS-CoV-2 have resulted ineffective. In this succinct review, we discuss the different potential targets in SARS-CoV-2 at both the genomic and proteomic levels. In addition, we analyze the compounds inhibiting individual target protein as well as multiple targets of SARS-CoV-2. ACE-2 receptor in humans has also been considered a target, keeping the role of the receptor in mind. The mechanism of action of these compounds has also been highlighted along with their clinical manifestation. Towards the end of the review, a brief note on the drugs currently in clinical trials and the current status of the vaccines are also examined. In conclusion, compounds targeting multiple targets of the virus hold the key in putting an end to the coronavirus malady.Communicated by Ramaswamy H. Sarma.

Genomic variation and point mutations analysis of Indian COVID-19 patient samples submitted in GISAID database

Corona virus disease 2019 (COVID-19) endemic has havoc on the world; the causative virus of the pandemic is SARS CoV-2. Pharmaceutical companies and academic institutes are in continuous efforts to identify anti-viral therapy or vaccines, but the most significant challenge faced is the highly evolving genome of SARS CoV-2, which is imparting evolutionary selective benefits to the virus. To understand the viral mutations, we have retrieved nine hundred and thirty-four samples from different states of India via the GISAID database and analyzed the frequency of all types of point mutation in all structural, non-structural proteins, and accessory factors of SARS CoV-2. Spike glycol protein, nsp3, nsp6, nsp12, N and NS3 were the most evolving proteins. High frequency point mutations were Q496P (nsp2), A380V (nsp4), A994D (nsp3), L37F (nsp6), P323L & A97V (nsp12), Q57H (ns3), D614G (S), P13L (N), R203K (N), G204R (N) and S194L (N).

SARS-CoV-2 structural coverage map reveals viral protein assembly, mimicry, and hijacking mechanisms

We modeled 3D structures of all SARS-CoV-2 proteins, generating 2,060 models that span 69% of the viral proteome and provide details not available elsewhere. We found that ˜6% of the proteome mimicked human proteins, while ˜7% was implicated in hijacking mechanisms that reverse post-translational modifications, block host translation, and disable host defenses; a further ˜29% self-assembled into heteromeric states that provided insight into how the viral replication and translation complex forms. To make these 3D models more accessible, we devised a structural coverage map, a novel visualization method to show what is-and is not-known about the 3D structure of the viral proteome. We integrated the coverage map into an accompanying online resource (https://aquaria.ws/covid) that can be used to find and explore models corresponding to the 79 structural states identified in this work. The resulting Aquaria-COVID resource helps scientists use emerging structural data to understand the mechanisms underlying coronavirus infection and draws attention to the 31% of the viral proteome that remains structurally unknown or dark.

Structural phylogenetic analysis reveals lineage-specific RNA repetitive structural motifs in all coronaviruses and associated variations in SARS-CoV-2

In many single-stranded (ss) RNA viruses, the cis-acting packaging signal that confers selectivity genome packaging usually encompasses short structured RNA repeats. These structural units, termed repetitive structural motifs (RSMs), potentially mediate capsid assembly by specific RNA–protein interactions. However, general knowledge of the conservation and/or the diversity of RSMs in the positive-sense ssRNA coronaviruses (CoVs) is limited. By performing structural phylogenetic analysis, we identified a variety of RSMs in nearly all CoV genomic RNAs, which are exclusively located in the 5′-untranslated regions (UTRs) and/or in the inter-domain regions of poly-protein 1ab coding sequences in a lineage-specific manner. In all alpha- and beta-CoVs, except for Embecovirus spp, two to four copies of 5′-gUUYCGUc-3′ RSMs displaying conserved hexa-loop sequences were generally identified in Stem-loop 5 (SL5) located in the 5′-UTRs of genomic RNAs. In Embecovirus spp., however, two to eight copies of 5′-agc-3′/guAAu RSMs were found in the coding regions of non-structural protein (NSP) 3 and/or NSP15 in open reading frame (ORF) 1ab. In gamma- and delta-CoVs, other types of RSMs were found in several clustered structural elements in 5′-UTRs and/or ORF1ab. The identification of RSM-encompassing structural elements in all CoVs suggests that these RNA elements play fundamental roles in the life cycle of CoVs. In the recently emerged SARS-CoV-2, beta-CoV-specific RSMs are also found in its SL5, displaying two copies of 5′-gUUUCGUc-3′ motifs. However, multiple sequence alignment reveals that the majority of SARS-CoV-2 possesses a variant RSM harboring SL5b C241U, and intriguingly, several variations in the coding sequences of viral proteins, such as Nsp12 P323L, S protein D614G, and N protein R203K-G204R, are concurrently found with such variant RSM. In conclusion, the comprehensive exploration for RSMs reveals phylogenetic insights into the RNA structural elements in CoVs as a whole and provides a new perspective on variations currently found in SARS-CoV-2.

Large-Scale Recombinant Production of the SARS-CoV-2 Proteome for High-Throughput and Structural Biology Applications

The highly infectious disease COVID-19 caused by the Betacoronavirus SARS-CoV-2 poses a severe threat to humanity and demands the redirection of scientific efforts and criteria to organized research projects. The international COVID19-NMR consortium seeks to provide such new approaches by gathering scientific expertise worldwide. In particular, making available viral proteins and RNAs will pave the way to understanding the SARS-CoV-2 molecular components in detail. The research in COVID19-NMR and the resources provided through the consortium are fully disclosed to accelerate access and exploitation. NMR investigations of the viral molecular components are designated to provide the essential basis for further work, including macromolecular interaction studies and high-throughput drug screening. Here, we present the extensive catalog of a holistic SARS-CoV-2 protein preparation approach based on the consortium's collective efforts. We provide protocols for the large-scale production of more than 80% of all SARS-CoV-2 proteins or essential parts of them. Several of the proteins were produced in more than one laboratory, demonstrating the high interoperability between NMR groups worldwide. For the majority of proteins, we can produce isotope-labeled samples of HSQC-grade. Together with several NMR chemical shift assignments made publicly available on covid19-nmr.com, we here provide highly valuable resources for the production of SARS-CoV-2 proteins in isotope-labeled form.

A molecular dynamics simulation study of the ACE2 receptor with screened natural inhibitors to identify novel drug candidate against COVID-19

Background & Objectives

The massive outbreak of Novel Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2) has turned out to be a serious global health issue worldwide. Currently, no drugs or vaccines are available for the treatment of COVID-19. The current computational study was attempted to identify a novel therapeutic inhibitor against novel SARS-CoV-2 using in silico drug discovery pipeline.

Methods

In the present study, the human angiotensin-converting enzyme 2 (ACE2) receptor was the target for the designing of drugs against the deadly virus. The 3D structure of the receptor was modeled & validated using a Swiss-model, Procheck & Errat server. A molecular docking study was performed between a group of natural & synthetic compounds having proven anti-viral activity with ACE2 receptor using Autodock tool 1.5.6. The molecular dynamics simulation study was performed using Desmond v 12 to evaluate the stability and interaction of the ACE2 receptor with a ligand.

Results

Based on the lowest binding energy, confirmation, and H-bond interaction, cinnamic acid (−5.20 kcal/mol), thymoquinone (−4.71 kcal/mol), and andrographolide (Kalmegh) (−4.00 kcal/mol) were screened out showing strong binding affinity to the active site of ACE2 receptor. MD simulations suggest that cinnamic acid, thymoquinone, and andrographolide (Kalmegh) could efficiently activate the biological pathway without changing the conformation in the binding site of the ACE2 receptor. The bioactivity and drug-likeness properties of compounds show their better pharmacological property and safer to use.

Interpretation & Conclusions

The study concludes the high potential of cinnamic acid, thymoquinone, and andrographolide against the SARS-CoV-2 ACE2 receptor protein. Thus, the molecular docking and MD simulation study will aid in understanding the molecular interaction between ligand and receptor binding site, thereby leading to novel therapeutic intervention.

1H,13C and 15N chemical shift assignments of the SUD domains of SARS-CoV-2 non-structural protein 3c: "the N-terminal domain-SUD-N"

Among the proteins encoded by the SARS-CoV-2 RNA, nsP3 (non-structural Protein3) is the largest multi-domain protein. Its role is multifaceted and important for the viral life cycle. Nonetheless, regarding the specific role of each domain there are many aspects of their function that have to be investigated. SARS Unique Domains (SUDs), constitute the nsP3c region of the nsP3, and were observed for the first time in SARS-CoV. Two of them, namely SUD-N (the first SUD) and the SUD-M (sequential to SUD-N), exhibit structural homology with nsP3b ("X" or macro domain); indeed all of them are folded in a three-layer α/β/α sandwich. On the contrary, they do not exhibit functional similarities, like ADP-ribose binding properties and ADP-ribose hydrolase activity. There are reports that suggest that these two SUDs may exhibit a binding selectivity towards G-oligonucleotides, a feature which may contribute to the characterization of their role in the formation of the replication/transcription viral complex (RTC) and of the interaction of various viral "components" with the host cell. While the structures of these domains of SARS-CoV-2 have not been determined yet, SUDs interaction with oligonucleotides and/or RNA molecules may provide a platform for drug discovery. Here, we report the almost complete NMR backbone and side-chain resonance assignment (¹H,¹³C,¹⁵N) of SARS-CoV-2 SUD-N protein, and the NMR chemical shift-based prediction of the secondary structure elements. These data may be exploited for its 3D structure determination and the screening of chemical compounds libraries, which may alter SUD-N function.

1H,13C and 15N chemical shift assignments of the SUD domains of SARS-CoV-2 non-structural protein 3c: "The SUD-M and SUD-C domains"

SARS-CoV-2 RNA, nsP3c (non-structural Protein3c) spans the sequence of the so-called SARS Unique Domains (SUDs), first observed in SARS-CoV. Although the function of this viral protein is not fully elucidated, it is believed that it is crucial for the formation of the replication/transcription viral complex (RTC) and of the interaction of various viral "components" with the host cell; thus, it is essential for the entire viral life cycle. The first two SUDs, the so-called SUD-N (the N-terminal domain) and SUD-M (domain following SUD-N) domains, exhibit topological and conformational features that resemble the nsP3b macro (or "X") domain. Indeed, they are all folded in a three-layer α/β/α sandwich structure, as revealed through crystallographic structural investigation of SARS-CoV SUDs, and they have been attributed to different substrate selectivity as they selectively bind to oligonucleotides. On the other hand, the C-terminal SUD (SUD-C) exhibit much lower sequence similarities compared to the SUD-N & SUD-M, as reported in previous crystallographic and NMR studies of SARS-CoV. In the absence of the 3D structures of SARS-CoV-2, we report herein the almost complete NMR backbone and side-chain resonance assignment (¹H,¹³C,¹⁵N) of SARS-CoV-2 SUD-M and SUD-C proteins, and the NMR chemical shift-based prediction of their secondary structure elements. These NMR data will set the base for further understanding at the atomic-level conformational dynamics of these proteins and will allow the effective screening of a large number of small molecules as binders with potential biological impact on their function.

Current Understanding of Novel Coronavirus: Molecular Pathogenesis, Diagnosis, and Treatment Approaches

An outbreak of “Pneumonia of Unknown Etiology” occurred in Wuhan, China, in late December 2019. Later, the agent factor was identified and coined as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and the disease was named coronavirus disease 2019 (COVID-19). In a shorter period, this newly emergent infection brought the world to a standstill. On 11 March 2020, the WHO declared COVID-19 as a pandemic. Researchers across the globe have joined their hands to investigate SARS-CoV-2 in terms of pathogenicity, transmissibility, and deduce therapeutics to subjugate this infection. The researchers and scholars practicing different arts of medicine are on an extensive quest to come up with safer ways to curb the pathological implications of this viral infection. A huge number of clinical trials are underway from the branch of allopathy and naturopathy. Besides, a paradigm shift on cellular therapy and nano-medicine protocols has to be optimized for better clinical and functional outcomes of COVID-19-affected individuals. This article unveils a comprehensive review of the pathogenesis mode of spread, and various treatment modalities to combat COVID-19 disease.

Genome composition and genetic characterization of SARS-CoV-2

SARS-CoV-2 is a type of Betacoronaviruses responsible for COVID-19 pandemic disease, with more than 1.745 million fatalities globally as of December-2020. Genetically, it is considered the second largest genome of all RNA viruses with a 5' cap and 3' poly-A tail. Phylogenetic analyses of coronaviruses reveal that SARS-CoV-2 is genetically closely related to the Bat-SARS Like-Corona virus (Bat-SL-Cov) with 96% whole-genome identity. SARS-CoV-2 genome consists of 15 ORFs coded into 29 proteins. At the 5' terminal of the genome, we have ORF1ab and ORF1a, which encode the 1ab and 1a polypeptides that are proteolytically cleaved into 16 different nonstructural proteins (NSPs). The 3' terminal of the genome represents four structural (spike, envelope, matrix, and nucleocapsid) and nine accessory (3a, 3b, 6, 7a, 7b, 8b, 9a, 9b, and orf10) proteins. As the number of COVID-19 patients increases dramatically worldwide, there is an urgent need to find a quick and sensitive diagnostic tool for controlling the outbreak of SARS-CoV-2 in the community. Today, molecular testing methods utilizing viral genetic material (e.g., PCR) represent the crucial diagnostic tool for the SARS-CoV-2 virus despite its low sensitivity in the early stage of viral infection. This review summarizes the genome composition and genetic characterization of the SARS-CoV-2.

Latent periodicity-2 in coronavirus SARS-CoV-2 genome: Evolutionary implications

The ongoing global pandemic of infection disease COVID-19 caused by the 2019 novel coronavirus (SARS-COV-2, formerly 2019-nCoV) presents critical threats to public health and the economy. The genome of SARS-CoV-2 had been sequenced and structurally annotated, yet little is known of the intrinsic organization and evolution of the genome. To this end, we present a mathematical method for the genomic spectrum, a kind of barcode, of SARS-CoV-2 and common human coronaviruses. The genomic spectrum is constructed according to the periodic distributions of nucleotides and therefore reflects the unique characteristics of the genome. The results demonstrate that coronavirus SARS-CoV-2 exhibits predominant latent periodicity-2 regions of non-structural proteins 3, 4, 5, and 6. Further analysis of the latent periodicity-2 regions suggests that the dinucleotide imbalances are increased during evolution and may confer the evolutionary fitness of the virus. Especially, SARS-CoV-2 isolates have increased latent periodicity-2 and periodicity-3 during COVID-19 pandemic. The special strong periodicity-2 regions and the intensity of periodicity-2 in the SARS-CoV-2 whole genome may become diagnostic and pharmaceutical targets in monitoring and curing the COVID-19 disease.

Functional and druggability analysis of the SARS-CoV-2 proteome

The infectious coronavirus disease (COVID-19) pandemic, caused by the coronavirus SARS-CoV-2, appeared in December 2019 in Wuhan, China, and has spread worldwide. As of today, more than 46 million people have been infected and over 1.2 million fatalities. With the purpose of contributing to the development of effective therapeutics, we performed an in silico determination of binding hot-spots and an assessment of their druggability within the complete SARS-CoV-2 proteome. All structural, non-structural, and accessory proteins have been studied, and whenever experimental structural data of SARS-CoV-2 proteins were not available, homology models were built based on solved SARS-CoV structures. Several potential allosteric or protein-protein interaction druggable sites on different viral targets were identified, knowledge that could be used to expand current drug discovery endeavors beyond the currently explored cysteine proteases and the polymerase complex. It is our hope that this study will support the efforts of the scientific community both in understanding the molecular determinants of this disease and in widening the repertoire of viral targets in the quest for repurposed or novel drugs against COVID-19.

Potentially adaptive SARS-CoV-2 mutations discovered with novel spatiotemporal and explainable AI models

BACKGROUND

A mechanistic understanding of the spread of SARS-CoV-2 and diligent tracking of ongoing mutagenesis are of key importance to plan robust strategies for confining its transmission. Large numbers of available sequences and their dates of transmission provide an unprecedented opportunity to analyze evolutionary adaptation in novel ways. Addition of high-resolution structural information can reveal the functional basis of these processes at the molecular level. Integrated systems biology-directed analyses of these data layers afford valuable insights to build a global understanding of the COVID-19 pandemic.

RESULTS

Here we identify globally distributed haplotypes from 15,789 SARS-CoV-2 genomes and model their success based on their duration, dispersal, and frequency in the host population. Our models identify mutations that are likely compensatory adaptive changes that allowed for rapid expansion of the virus. Functional predictions from structural analyses indicate that, contrary to previous reports, the Asp614Gly mutation in the spike glycoprotein (S) likely reduced transmission and the subsequent Pro323Leu mutation in the RNA-dependent RNA polymerase led to the precipitous spread of the virus. Our model also suggests that two mutations in the nsp13 helicase allowed for the adaptation of the virus to the Pacific Northwest of the USA. Finally, our explainable artificial intelligence algorithm identified a mutational hotspot in the sequence of S that also displays a signature of positive selection and may have implications for tissue or cell-specific expression of the virus.

CONCLUSIONS

These results provide valuable insights for the development of drugs and surveillance strategies to combat the current and future pandemics.

Evolution of the SARS-CoV-2 proteome in three dimensions (3D) during the first six months of the COVID-19 pandemic

Three-dimensional structures of SARS-CoV-2 and other coronaviral proteins archived in the Protein Data Bank were used to analyze viral proteome evolution during the first six months of the COVID-19 pandemic. Analyses of spatial locations, chemical properties, and structural and energetic impacts of the observed amino acid changes in >48,000 viral proteome sequences showed how each one of the 29 viral study proteins have undergone amino acid changes. Structural models computed for every unique sequence variant revealed that most substitutions map to protein surfaces and boundary layers with a minority affecting hydrophobic cores. Conservative changes were observed more frequently in cores versus boundary layers/surfaces. Active sites and protein-protein interfaces showed modest numbers of substitutions. Energetics calculations showed that the impact of substitutions on the thermodynamic stability of the proteome follows a universal bi-Gaussian distribution. Detailed results are presented for six drug discovery targets and four structural proteins comprising the virion, highlighting substitutions with the potential to impact protein structure, enzyme activity, and functional interfaces. Characterizing the evolution of the virus in three dimensions provides testable insights into viral protein function and should aid in structure-based drug discovery efforts as well as the prospective identification of amino acid substitutions with potential for drug resistance.

Genomics functional analysis and drug screening of SARS-CoV-2

A novel coronavirus appeared in Wuhan, China has led to major outbreaks. Recently, rapid classification of virus species, analysis of genome and screening for effective drugs are the most important tasks. In the present study, through literature review, sequence alignment, ORF identification, motif recognition, secondary and tertiary structure prediction, the whole genome of SARS-CoV-2 were comprehensively analyzed. To find effective drugs, the parameters of binding sites were calculated by SeeSAR. In addition, potential miRNAs were predicted according to RNA base-pairing. After prediction by using NCBI, WebMGA and GeneMark and comparison, a total of 8 credible ORFs were detected. Even the whole genome have great difference with other CoVs, each ORF has high homology with SARS-CoVs (>90%). Furthermore, domain composition in each ORFs was also similar to SARS. In the DrugBank database, only 7 potential drugs were screened based on the sequence search module. Further predicted binding sites between drug and ORFs revealed that 2-(N-Morpholino)-ethanesulfonic acid could bind 1# ORF in 4 different regions ideally. Meanwhile, both benzyl (2-oxopropyl) carbamate and 4-(dimehylamina) benzoic acid have bene demonstrated to inhibit SARS-CoV infection effectively. Interestingly, 2 miRNAs (miR-1307-3p and miR-3613-5p) were predicted to prevent virus replication via targeting 3'-UTR of the genome or as biomarkers. In conclusion, the novel coronavirus may have consanguinity with SARS. Drugs used to treat SARS may also be effective against the novel virus. In addition, altering miRNA expression may become a potential therapeutic schedule.

1H, 13C, and 15N backbone chemical shift assignments of the nucleic acid-binding domain of SARS-CoV-2 non-structural protein 3e

The ongoing pandemic caused by the Betacoronavirus SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus-2) demonstrates the urgent need of coordinated and rapid research towards inhibitors of the COVID-19 lung disease. The covid19-nmr consortium seeks to support drug development by providing publicly accessible NMR data on the viral RNA elements and proteins. The SARS-CoV-2 genome encodes for approximately 30 proteins, among them are the 16 so-called non-structural proteins (Nsps) of the replication/transcription complex. The 217-kDa large Nsp3 spans one polypeptide chain, but comprises multiple independent, yet functionally related domains including the viral papain-like protease. The Nsp3e sub-moiety contains a putative nucleic acid-binding domain (NAB) with so far unknown function and consensus target sequences, which are conceived to be both viral and host RNAs and DNAs, as well as protein-protein interactions. Its NMR-suitable size renders it an attractive object to study, both for understanding the SARS-CoV-2 architecture and drugability besides the classical virus' proteases. We here report the near-complete NMR backbone chemical shifts of the putative Nsp3e NAB that reveal the secondary structure and compactness of the domain, and provide a basis for NMR-based investigations towards understanding and interfering with RNA- and small-molecule-binding by Nsp3e.

Coronaviruses: An Updated Overview of Their Replication and Pathogenesis

Coronaviruses (CoVs), enveloped positive-sense RNA viruses, are characterized by club-like spikes that project from their surface, an unusually large RNA genome, and a unique replication strategy. CoVs cause a variety of diseases in mammals and birds ranging from enteritis in cows and pigs, and upper respiratory tract and kidney disease in chickens to lethal human respiratory infections. Most recently, the novel coronavirus, SARS-CoV-2, which was first identified in Wuhan, China in December 2019, is the cause of a catastrophic pandemic, COVID-19, with more than 8 million infections diagnosed worldwide by mid-June 2020. Here we provide a brief introduction to CoVs discussing their replication, pathogenicity, and current prevention and treatment strategies. We will also discuss the outbreaks of the highly pathogenic Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV), which are relevant for understanding COVID-19.

The molecular virology of coronaviruses

Few human pathogens have been the focus of as much concentrated worldwide attention as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of COVID-19. Its emergence into the human population and ensuing pandemic came on the heels of severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), two other highly pathogenic coronavirus spillovers, which collectively have reshaped our view of a virus family previously associated primarily with the common cold. It has placed intense pressure on the collective scientific community to develop therapeutics and vaccines, whose engineering relies on a detailed understanding of coronavirus biology. Here, we present the molecular virology of coronavirus infection, including its entry into cells, its remarkably sophisticated gene expression and replication mechanisms, its extensive remodeling of the intracellular environment, and its multifaceted immune evasion strategies. We highlight aspects of the viral life cycle that may be amenable to antiviral targeting as well as key features of its biology that await discovery.

A comprehensive review about SARS-CoV-2

The coronavirus disease (COVID-19) was first identified in China, December 2019. Since then, it has spread the length and breadth of the world at an unprecedented, alarming rate. Severe acute respiratory syndrome coronavirus (SARS-CoV)-2, which causes COVID-19, has much in common with its closest homologs, SARS-CoV and Middle East respiratory syndrome-CoV. The virus-host interaction of SARS-CoV-2 uses the same receptor, ACE2, which is similar to that of SARS-CoV, which spreads through the respiratory tract. Patients with COVID-19 report symptoms including mild-to-severe fever, cough and fatigue; very few patients report gastrointestinal infections. There are no specific antiviral strategies. A few strong medications are under investigation, so we have to focus on proposals which ought to be taken to forestall this infection in a living host.

Why do SARS-CoV-2 NSPs rush to the ER?

SARS-CoV-2, which led to the 2020 global pandemic, is responsible for the Coronavirus Disease 2019 (COVID-19), a respiratory illness, and presents a tropism for the central nervous system. Like most members of this family, the virus is composed of structural and non-structural proteins (NSPs). The non-structural proteins are critical elements of the replication and transcription complex (RTC), as well as immune system evasion. Through hijacking the endoplasmic reticulum (ER) membrane, NSPs help the virus establish the RTC, inducing ER stress after membrane rearrangement and causing severe neuronal disturbance. In this review, we focus on the role of Nsp3, 4, and 6 in intracellular membrane rearrangement and evaluate the potential disruption of the central nervous system and the neurodegeneration which it could trigger. Studies of these NSPs will not only bring to light their specific role in viral infection but also facilitate the discovery of novel targeted drugs.

Molecular Basis for ADP-Ribose Binding to the Mac1 Domain of SARS-CoV-2 nsp3

The virus that causes COVID-19, SARS-CoV-2, has a large RNA genome that encodes numerous proteins that might be targets for antiviral drugs. Some of these proteins, such as the RNA-dependent RNA polymerase, helicase, and main protease, are well conserved between SARS-CoV-2 and the original SARS virus, but several others are not. This study examines one of the proteins encoded by SARS-CoV-2 that is most different, a macrodomain of nonstructural protein 3 (nsp3). Although 26% of the amino acids in this SARS-CoV-2 macrodomain differ from those observed in other coronaviruses, biochemical and structural data reveal that the protein retains the ability to bind ADP-ribose, which is an important characteristic of beta coronaviruses and a potential therapeutic target.

COVID-19: Emergence of Infectious Diseases, Nanotechnology Aspects, Challenges, and Future Perspectives

Wuhan, a city of China, is the epicenter for the pandemic outbreak of coronavirus disease-2019 (COVID-19). It has become a severe public health challenge to the world and established a public health emergency of international worry. This infectious disease has pulled down the economy of almost all top developed nations. The coronaviruses (CoVs) known for various epidemics caused time to time. Infectious diseases such as severe acute respiratory syndrome (SARS) and middle east respiratory syndrome (MERS), followed by COVID-19, are all coronaviruses led outbreaks that scourged the history of mankind. CoVs evolved themselves to more infectious, transmissible, and more pandemic with time. To prevent the spread of the SARS-CoV-2, many countries have ordered the complete lockdown to combat the outbreak. This paper briefly discussed the historical background of CoVs and the evolution of human coronaviruses (HCoVs), the case studies and the development of their antiviral medications. The viral infection encountered with present-day challenges and futuristic approaches with the help of nanotechnology to minimize the spread of infectious viruses. The antiviral drugs and their clinical advances, along with herbal medicines for viral inhibition and immunity boosters, are described. Elaboration of tables related to CoVs for the compilation of the literature has been adopted for the better understanding.

Betacoronavirus Genomes: How Genomic Information has been Used to Deal with Past Outbreaks and the COVID-19 Pandemic

In the 21st century, three highly pathogenic betacoronaviruses have emerged, with an alarming rate of human morbidity and case fatality. Genomic information has been widely used to understand the pathogenesis, animal origin and mode of transmission of coronaviruses in the aftermath of the 2002-2003 severe acute respiratory syndrome (SARS) and 2012 Middle East respiratory syndrome (MERS) outbreaks. Furthermore, genome sequencing and bioinformatic analysis have had an unprecedented relevance in the battle against the 2019-2020 coronavirus disease 2019 (COVID-19) pandemic, the newest and most devastating outbreak caused by a coronavirus in the history of mankind. Here, we review how genomic information has been used to tackle outbreaks caused by emerging, highly pathogenic, betacoronavirus strains, emphasizing on SARS-CoV, MERS-CoV and SARS-CoV-2. We focus on shared genomic features of the betacoronaviruses and the application of genomic information to phylogenetic analysis, molecular epidemiology and the design of diagnostic systems, potential drugs and vaccine candidates.

Review on COVID-19: Rise of SARS-CoV-2 Pandemic Outbreak

Initially recognized of COVID-19 within the world in 2019, the World Health Organization situational report from May 22nd, 2020, globally, there is a complete of 5,204,508 confirmed cases, with 212 countries being affected by the novel coronavirus. 2019 novel coronavirus (SARS-CoV-2) is that the seventh member of the family of coronaviruses is enveloped viruses with a positive sense, single-stranded RNA genome. The SARS-CoV-2 may be a �-CoV of group 2B there is 70% comparability in genetic sequence to SARS-CoV. The source of the new coronavirus infection has been resolved as bats. With whole-genome sequences of SARS-CoV-2 is 96% comparatively at the whole-genome level to a bat coronavirus. Mechanisms of transmission are concluded to incorporate contact, droplet, and possibly airborne under certain circumstances supported ancient experiences associated with SARS-CoV outbreaks. Although antiretroviral therapy is being widely used everywhere the globe for such patents, effects at finding a SARS-CoV vaccine haven�t succeeded so far.

Genotyping coronavirus SARS-CoV-2: methods and implications

The emerging global infectious COVID-19 disease by novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) presents critical threats to global public health and the economy since it was identified in late December 2019 in China. The virus has gone through various pathways of evolution. To understand the evolution and transmission of SARS-CoV-2, genotyping of virus isolates is of great importance. This study presents an accurate method for effectively genotyping SARS-CoV-2 viruses using complete genomes. The method employs the multiple sequence alignments of the genome isolates with the SARS-CoV-2 reference genome. The single-nucleotide polymorphism (SNP) genotypes are then measured by Jaccard distances to track the relationship of virus isolates. The genotyping analysis of SARS-CoV-2 isolates from the globe reveals that specific multiple mutations are the predominated mutation type during the current epidemic. The proposed method serves an effective tool for monitoring and tracking the epidemic of pathogenic viruses in their global and local genetic variations. The genotyping analysis shows that the genes encoding the S proteins and RNA polymerase, RNA primase, and nucleoprotein, undergo frequent mutations. These mutations are critical for vaccine development in disease control.

Emerging coronaviruses: Genome structure, replication, and pathogenesis

The recent emergence of a novel coronavirus (2019-nCoV), which is causing an outbreak of unusual viral pneumonia in patients in Wuhan, a central city in China, is another warning of the risk of CoVs posed to public health. In this minireview, we provide a brief introduction of the general features of CoVs and describe diseases caused by different CoVs in humans and animals. This review will help understand the biology and potential risk of CoVs that exist in richness in wildlife such as bats.

13C Chemical Shifts in Proteins: A Rich Source of Encoded Structural Information

Despite the formidable progress in Nuclear Magnetic Resonance (NMR) spectroscopy, quality assessment of NMR-derived structures remains as an important problem. Thus, validation of protein structures is essential for the spectroscopists, since it could enable them to detect structural flaws and potentially guide their efforts in further refinement. Moreover, availability of accurate and efficient validation tools would help molecular biologists and computational chemists to evaluate quality of available experimental structures and to select a protein model which is the most suitable for a given scientific problem. The ¹³C^α nuclei are ubiquitous in proteins, moreover, their shieldings are easily obtainable from NMR experiments and represent a rich source of encoded structural information that makes ¹³C^α chemical shifts an attractive candidate for use in computational methods aimed at determination and validation of protein structures. In this chapter, the basis of a novel methodology of computing, at the quantum chemical level of theory, the ¹³C^α shielding for the amino acid residues in proteins is described. We also identify and examine the main factors affecting the ¹³C^α-shielding computation. Finally, we illustrate how the information encoded in the ¹³C chemical shifts can be used for a number of applications, viz., from protein structure prediction of both α-helical and β-sheet conformations, to determination of the fraction of the tautomeric forms of the imidazole ring of histidine in proteins as a function of pH or to accurate detection of structural flaws, at a residue-level, in NMR-determined protein models.

Nsp3 of coronaviruses: Structures and functions of a large multi-domain protein

The multi-domain non-structural protein 3 (Nsp3) is the largest protein encoded by the coronavirus (CoV) genome, with an average molecular mass of about 200 kD. Nsp3 is an essential component of the replication/transcription complex. It comprises various domains, the organization of which differs between CoV genera, due to duplication or absence of some domains. However, eight domains of Nsp3 exist in all known CoVs: the ubiquitin-like domain 1 (Ubl1), the Glu-rich acidic domain (also called “hypervariable region”), a macrodomain (also named “X domain”), the ubiquitin-like domain 2 (Ubl2), the papain-like protease 2 (PL2^pro), the Nsp3 ectodomain (3Ecto, also called “zinc-finger domain”), as well as the domains Y1 and CoV-Y of unknown functions. In addition, the two transmembrane regions, TM1 and TM2, exist in all CoVs. The three-dimensional structures of domains in the N-terminal two thirds of Nsp3 have been investigated by X-ray crystallography and/or nuclear magnetic resonance (NMR) spectroscopy since the outbreaks of Severe Acute Respiratory Syndrome coronavirus (SARS-CoV) in 2003 as well as Middle-East Respiratory Syndrome coronavirus (MERS-CoV) in 2012. In this review, the structures and functions of these domains of Nsp3 are discussed in depth.

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Nonstructural protein 3 (∼200 kD) is a multifunctional protein comprising up to 16 different domains and regions.

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Nsp3 binds to viral RNA, nucleocapsid protein, as well as other viral proteins, and participates in polyprotein processing.

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The papain-like protease of Nsp3 is an established target for new antivirals.

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Through its de-ADP-ribosylating, de-ubiquitinating, and de-ISGylating activities, Nsp3 counteracts host innate immunity.

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Structural data are available for the N-terminal two thirds of Nsp3, but domains in the remainder are poorly characterized.

Detection and characterization of diverse alpha- and betacoronaviruses from bats in China

Bats have been implicated as important reservoir hosts of alpha- and betacoronaviruses. In this study, diverse coronaviruses (CoVs) were detected in 50 of 951 (positive rate 5.3%) intestinal specimens of eight bat species collected in four provinces and the Tibet Autonomous Region of China by pan-coronavirus RT-PCR screening. Based on 400-nt RNA-dependent RNA polymerase (RdRP) sequence analysis, eight belonged to genus Alphacoronavirus and 42 to Betacoronavirus. Among the 50 positive specimens, thirteen gave rise to CoV full-length RdRP gene amplification for further sequence comparison, of which three divergent sequences (two from a unreported province) were subjected to full genome sequencing. Two complete genomes of betacoronaviruses (JTMC15 and JPDB144) and one nearly-complete genome of alphacoronavirus (JTAC2) were sequenced and their genomic organization predicted. The present study has identified additional numbers of genetically diverse bat-borne coronaviruses with a wide distribution in China. Two new species of bat CoV, identified through sequence comparison and phylogenetic analysis, are proposed.

X-ray Structural and Functional Studies of the Three Tandemly Linked Domains of Non-structural Protein 3 (nsp3) from Murine Hepatitis Virus Reveal Conserved Functions

Murine hepatitis virus (MHV) has long served as a model system for the study of coronaviruses. Non-structural protein 3 (nsp3) is the largest nsp in the coronavirus genome, and it contains multiple functional domains that are required for coronavirus replication. Despite the numerous functional studies on MHV and its nsp3 domain, the structure of only one domain in nsp3, the small ubiquitin-like domain 1 (Ubl1), has been determined. We report here the x-ray structure of three tandemly linked domains of MHV nsp3, including the papain-like protease 2 (PLP2) catalytic domain, the ubiquitin-like domain 2 (Ubl2), and a third domain that we call the DPUP (domain preceding Ubl2 and PLP2) domain. DPUP has close structural similarity to the severe acute respiratory syndrome coronavirus unique domain C (SUD-C), suggesting that this domain may not be unique to the severe acute respiratory syndrome coronavirus. The PLP2 catalytic domain was found to have both deubiquitinating and deISGylating isopeptidase activities in addition to proteolytic activity. A computationally derived model of MHV PLP2 bound to ubiquitin was generated, and the potential interactions between ubiquitin and PLP2 were probed by site-directed mutagenesis. These studies extend substantially our structural knowledge of MHV nsp3, providing a platform for further investigation of the role of nsp3 domains in MHV viral replication.

A G-quadruplex-binding macrodomain within the "SARS-unique domain" is essential for the activity of the SARS-coronavirus replication-transcription complex

The multi-domain non-structural protein 3 of SARS-coronavirus is a component of the viral replication/transcription complex (RTC). Among other domains, it contains three sequentially arranged macrodomains: the X domain and subdomains SUD-N as well as SUD-M within the “SARS-unique domain”. The X domain was proposed to be an ADP-ribose-1”-phosphatase or a poly(ADP-ribose)-binding protein, whereas SUD-NM binds oligo(G)-nucleotides capable of forming G-quadruplexes. Here, we describe the application of a reverse genetic approach to assess the importance of these macrodomains for the activity of the SARS-CoV RTC. To this end, Renilla luciferase-encoding SARS-CoV replicons with selectively deleted macrodomains were constructed and their ability to modulate the RTC activity was examined. While the SUD-N and the X domains were found to be dispensable, the SUD-M domain was crucial for viral genome replication/transcription. Moreover, alanine replacement of charged amino-acid residues of the SUD-M domain, which are likely involved in G-quadruplex-binding, caused abrogation of RTC activity.

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A SARS-CoV replicon encoding Renilla luciferase as reporter protein is constructed.

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The role of three macrodomains for the replication/transcription complex is analyzed.

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In contrast to macrodomains X and SUD-N, SUD-M is found indispensable for replication.

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Site-directed mutagenesis identifies charged SUD-M residues required for replication.

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These residues have previously been shown to be involved in G-quadruplex binding.

Dissection of amino-terminal functional domains of murine coronavirus nonstructural protein 3

Coronaviruses, the largest RNA viruses, have a complex program of RNA synthesis that entails genome replication and transcription of subgenomic mRNAs. RNA synthesis by the prototype coronavirus mouse hepatitis virus (MHV) is carried out by a replicase-transcriptase composed of 16 nonstructural protein (nsp) subunits. Among these, nsp3 is the largest and the first to be inserted into the endoplasmic reticulum. nsp3 comprises multiple structural domains, including two papain-like proteases (PLPs) and a highly conserved ADP-ribose-1″-phosphatase (ADRP) macrodomain. We have previously shown that the ubiquitin-like domain at the amino terminus of nsp3 is essential and participates in a critical interaction with the viral nucleocapsid protein early in infection. In the current study, we exploited atypical expression schemes to uncouple PLP1 from the processing of nsp1 and nsp2 in order to investigate the requirements of nsp3 domains for viral RNA synthesis. In the first strategy, a mutant was created in which replicase polyprotein translation initiated with nsp3, thereby establishing that complete elimination of nsp1 and nsp2 does not abolish MHV viability. In the second strategy, a picornavirus autoprocessing element was used to separate a truncated nsp1 from nsp3. This provided a platform for further dissection of amino-terminal domains of nsp3. From this, we found that catalytic mutation of PLP1 or complete deletion of PLP1 and the adjacent ADRP domain was tolerated by the virus. These results showed that neither the PLP1 domain nor the ADRP domain of nsp3 provides integral activities essential for coronavirus genomic or subgenomic RNA synthesis.

IMPORTANCE

The largest component of the coronavirus replicase-transcriptase complex, nsp3, contains multiple modules, many of which do not have clearly defined functions in genome replication or transcription. These domains may play direct roles in RNA synthesis, or they may have evolved for other purposes, such as to combat host innate immunity. We initiated a dissection of MHV nsp3 aimed at identifying those activities or structures in this huge molecule that are essential to replicase activity. We found that both PLP1 and ADRP could be entirely deleted, provided that the requirement for proteolytic processing by PLP1 was offset by an alternative mechanism. This demonstrated that neither PLP1 nor ADRP plays an essential role in coronavirus RNA synthesis.

Coronaviruses: an overview of their replication and pathogenesis

Coronaviruses (CoVs), enveloped positive-sense RNA viruses, are characterized by club-like spikes that project from their surface, an unusually large RNA genome, and a unique replication strategy. Coronaviruses cause a variety of diseases in mammals and birds ranging from enteritis in cows and pigs and upper respiratory disease in chickens to potentially lethal human respiratory infections. Here we provide a brief introduction to coronaviruses discussing their replication and pathogenicity, and current prevention and treatment strategies. We also discuss the outbreaks of the highly pathogenic Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and the recently identified Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV).

Coronaviruses: an overview of their replication and pathogenesis

Coronaviruses (CoVs), enveloped positive-sense RNA viruses, are characterized by club-like spikes that project from their surface, an unusually large RNA genome, and a unique replication strategy. Coronaviruses cause a variety of diseases in mammals and birds ranging from enteritis in cows and pigs and upper respiratory disease in chickens to potentially lethal human respiratory infections. Here we provide a brief introduction to coronaviruses discussing their replication and pathogenicity, and current prevention and treatment strategies. We also discuss the outbreaks of the highly pathogenic Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and the recently identified Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV).

The SARS-coronavirus papain-like protease: structure, function and inhibition by designed antiviral compounds

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HTS and structure-based design produced naphthalene-based lead compounds with inhibition of SARS-CoV PLpro in the nM range.

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These naphthalene-based lead compounds have antiviral potency against SARS-CoV in cell culture.

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SARS-CoV PLpro naphthalene-based inhibitors are non-toxic and highly selective for SARS-CoV PLpro.

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Designed SARS-CoV PLpro inhibitors act through a non-covalent, competitive mechanism of inhibition.

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Lessons from design of SARS-CoV PLpro inhibitors have profound implications for other USPs implicated in disease processes.

Over 10 years have passed since the deadly human coronavirus that causes severe acute respiratory syndrome (SARS-CoV) emerged from the Guangdong Province of China. Despite the fact that the SARS-CoV pandemic infected over 8500 individuals, claimed over 800 lives and cost billions of dollars in economic loss worldwide, there still are no clinically approved antiviral drugs, vaccines or monoclonal antibody therapies to treat SARS-CoV infections. The recent emergence of the deadly human coronavirus that causes Middle East respiratory syndrome (MERS-CoV) is a sobering reminder that new and deadly coronaviruses can emerge at any time with the potential to become pandemics. Therefore, the continued development of therapeutic and prophylactic countermeasures to potentially deadly coronaviruses is warranted. The coronaviral proteases, papain-like protease (PLpro) and 3C-like protease (3CLpro), are attractive antiviral drug targets because they are essential for coronaviral replication. Although the primary function of PLpro and 3CLpro are to process the viral polyprotein in a coordinated manner, PLpro has the additional function of stripping ubiquitin and ISG15 from host-cell proteins to aid coronaviruses in their evasion of the host innate immune responses. Therefore, targeting PLpro with antiviral drugs may have an advantage in not only inhibiting viral replication but also inhibiting the dysregulation of signaling cascades in infected cells that may lead to cell death in surrounding, uninfected cells. This review provides an up-to-date discussion on the SARS-CoV papain-like protease including a brief overview of the SARS-CoV genome and replication followed by a more in-depth discussion on the structure and catalytic mechanism of SARS-CoV PLpro, the multiple cellular functions of SARS-CoV PLpro, the inhibition of SARS-CoV PLpro by small molecule inhibitors, and the prospect of inhibiting papain-like protease from other coronaviruses. This paper forms part of a series of invited articles in Antiviral Research on “From SARS to MERS: 10 years of research on highly pathogenic human coronaviruses.”

New insights on the role of paired membrane structures in coronavirus replication

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Coronavirus replication is tied to formation of double-membrane organelles (DMOs).

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DMO-making genes are conserved across the Nidovirales.

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Here, we interpret recent experiments on the role and importance of coronavirus DMOs.

The replication of coronaviruses, as in other positive-strand RNA viruses, is closely tied to the formation of membrane-bound replicative organelles inside infected cells. The proteins responsible for rearranging cellular membranes to form the organelles are conserved not just among the Coronaviridae family members, but across the order Nidovirales. Taken together, these observations suggest that the coronavirus replicative organelle plays an important role in viral replication, perhaps facilitating the production or protection of viral RNA. However, the exact nature of this role, and the specific contexts under which it is important have not been fully elucidated. Here, we collect and interpret the recent experimental evidence about the role and importance of membrane-bound organelles in coronavirus replication.

13C Chemical Shifts in Proteins: A Rich Source of Encoded Structural Information

Despite the formidable progress in Nuclear Magnetic Resonance (NMR) spectroscopy, quality assessment of NMR-derived structures remains as an important problem. Thus, validation of protein structures is essential for the spectroscopists, since it could enable them to detect structural flaws and potentially guide their efforts in further refinement. Moreover, availability of accurate and efficient validation tools would help molecular biologists and computational chemists to evaluate quality of available experimental structures and to select a protein model which is the most suitable for a given scientific problem. The ¹³C^α nuclei are ubiquitous in proteins, moreover, their shieldings are easily obtainable from NMR experiments and represent a rich source of encoded structural information that makes ¹³C^α chemical shifts an attractive candidate for use in computational methods aimed at determination and validation of protein structures. In this chapter, the basis of a novel methodology of computing, at the quantum chemical level of theory, the ¹³C^α shielding for the amino acid residues in proteins is described. We also identify and examine the main factors affecting the ¹³C^α-shielding computation. Finally, we illustrate how the information encoded in the ¹³C chemical shifts can be used for a number of applications, viz., from protein structure prediction of both α-helical and β-sheet conformations, to determination of the fraction of the tautomeric forms of the imidazole ring of histidine in proteins as a function of pH or to accurate detection of structural flaws, at a residue-level, in NMR-determined protein models.

Atlas of coronavirus replicase structure

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Complete and up to date coverage of replicase protein structures for SARS-CoV.

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Discusses SARS-CoV structure in the context of other coronavirus structures.

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Summarizes data from a variety of structural methods to illuminate protein function.

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Uses models and predictions to fill gaps in the SARS-CoV structure.

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Discusses the high percentage of novel protein folds among SARS-CoV proteins.

The international response to SARS-CoV has produced an outstanding number of protein structures in a very short time. This review summarizes the findings of functional and structural studies including those derived from cryoelectron microscopy, small angle X-ray scattering, NMR spectroscopy, and X-ray crystallography, and incorporates bioinformatics predictions where no structural data is available. Structures that shed light on the function and biological roles of the proteins in viral replication and pathogenesis are highlighted. The high percentage of novel protein folds identified among SARS-CoV proteins is discussed.

From SARS to MERS: 10 years of research on highly pathogenic human coronaviruses

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We review the outbreak of severe acute respiratory syndrome (SARS) in 2002–2003 and antiviral treatment of patients.

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We review efforts towards the rational design of anti-SARS therapeutics.

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We present a comprehensive list of all available 3-dimensional structures of coronavirus proteins.

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We discuss the emerging MERS coronavirus and review the few antivirals available for treatment.

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We critically discuss which lessons have been learned from SARS and which are yet to be learned.

This article introduces a series of invited papers in Antiviral Research marking the 10th anniversary of the outbreak of severe acute respiratory syndrome (SARS), caused by a novel coronavirus that emerged in southern China in late 2002. Until that time, coronaviruses had not been recognized as agents causing severe disease in humans, hence, the emergence of the SARS-CoV came as a complete surprise. Research during the past ten years has revealed the existence of a diverse pool of coronaviruses circulating among various bat species and other animals, suggesting that further introductions of highly pathogenic coronaviruses into the human population are not merely probable, but inevitable. The recent emergence of another coronavirus causing severe disease, Middle East respiratory syndrome (MERS), in humans, has made it clear that coronaviruses pose a major threat to human health, and that more research is urgently needed to elucidate their replication mechanisms, identify potential drug targets, and develop effective countermeasures. In this series, experts in many different aspects of coronavirus replication and disease will provide authoritative, up-to-date reviews of the following topics:

– clinical management and infection control of SARS;

– reservoir hosts of coronaviruses;

– receptor recognition and cross-species transmission of SARS-CoV;

– SARS-CoV evasion of innate immune responses;

– structures and functions of individual coronaviral proteins;

– anti-coronavirus drug discovery and development; and

– the public health legacy of the SARS outbreak.

Each article will be identified in the last line of its abstract as belonging to the series “From SARS to MERS: 10 years of research on highly pathogenic human coronaviruses.”

Characterization of a critical interaction between the coronavirus nucleocapsid protein and nonstructural protein 3 of the viral replicase-transcriptase complex

The coronavirus nucleocapsid protein (N) plays an essential structural role in virions through a network of interactions with positive-strand viral genomic RNA, the envelope membrane protein (M), and other N molecules. Additionally, N protein participates in at least one stage of the complex mechanism of coronavirus RNA synthesis. We previously uncovered an unanticipated interaction between N and the largest subunit of the viral replicase-transcriptase complex, nonstructural protein 3 (nsp3). This was found through analysis of revertants of a severely defective mutant of murine hepatitis virus (MHV) in which the N gene was replaced with that of its close relative, bovine coronavirus (BCoV). In the work reported here, we constructed BCoV chimeras and other mutants of MHV nsp3 and obtained complementary genetic evidence for its association with N protein. We found that the N-nsp3 interaction maps to the amino-terminal ubiquitin-like domain of nsp3, which is essential for the virus. The interaction does not require the adjacent acidic domain of nsp3, which is dispensable. In addition, we demonstrated a complete correspondence between N-nsp3 genetic interactions and the ability of N protein to enhance the infectivity of transfected coronavirus genomic RNA. The latter function of N was shown to depend on both of the RNA-binding domains of N, as well as on the serine- and arginine-rich central region of N, which binds nsp3. Our results support a model in which the N-nsp3 interaction serves to tether the genome to the newly translated replicase-transcriptase complex at a very early stage of infection.

Molecular determinants of severe acute respiratory syndrome coronavirus pathogenesis and virulence in young and aged mouse models of human disease

SARS coronavirus (SARS-CoV) causes severe acute respiratory tract disease characterized by diffuse alveolar damage and hyaline membrane formation. This pathology often progresses to acute respiratory distress (such as acute respiratory distress syndrome [ARDS]) and atypical pneumonia in humans, with characteristic age-related mortality rates approaching 50% or more in immunosenescent populations. The molecular basis for the extreme virulence of SARS-CoV remains elusive. Since young and aged (1-year-old) mice do not develop severe clinical disease following infection with wild-type SARS-CoV, a mouse-adapted strain of SARS-CoV (called MA15) was developed and was shown to cause lethal infection in these animals. To understand the genetic contributions to the increased pathogenesis of MA15 in rodents, we used reverse genetics and evaluated the virulence of panels of derivative viruses encoding various combinations of mouse-adapted mutations. We found that mutations in the viral spike (S) glycoprotein and, to a much less rigorous extent, in the nsp9 nonstructural protein, were primarily associated with the acquisition of virulence in young animals. The mutations in S likely increase recognition of the mouse angiotensin-converting enzyme 2 (ACE2) receptor not only in MA15 but also in two additional, independently isolated mouse-adapted SARS-CoVs. In contrast to the findings for young animals, mutations to revert to the wild-type sequence in nsp9 and the S glycoprotein were not sufficient to significantly attenuate the virus compared to other combinations of mouse-adapted mutations in 12-month-old mice. This panel of SARS-CoVs provides novel reagents that we have used to further our understanding of differential, age-related pathogenic mechanisms in mouse models of human disease.

Sequential nearest-neighbor effects on computed 13Calpha chemical shifts

To evaluate sequential nearest-neighbor effects on quantum-chemical calculations of (13)C(alpha) chemical shifts, we selected the structure of the nucleic acid binding (NAB) protein from the SARS coronavirus determined by NMR in solution (PDB id 2K87). NAB is a 116-residue alpha/beta protein, which contains 9 prolines and has 50% of its residues located in loops and turns. Overall, the results presented here show that sizeable nearest-neighbor effects are seen only for residues preceding proline, where Pro introduces an overestimation, on average, of 1.73 ppm in the computed (13)C(alpha) chemical shifts. A new ensemble of 20 conformers representing the NMR structure of the NAB, which was calculated with an input containing backbone torsion angle constraints derived from the theoretical (13)C(alpha) chemical shifts as supplementary data to the NOE distance constraints, exhibits very similar topology and comparable agreement with the NOE constraints as the published NMR structure. However, the two structures differ in the patterns of differences between observed and computed (13)C(alpha) chemical shifts, Delta(ca,i), for the individual residues along the sequence. This indicates that the Delta(ca,i)-values for the NAB protein are primarily a consequence of the limited sampling by the bundles of 20 conformers used, as in common practice, to represent the two NMR structures, rather than of local flaws in the structures.

An interaction between the nucleocapsid protein and a component of the replicase-transcriptase complex is crucial for the infectivity of coronavirus genomic RNA

The coronavirus nucleocapsid (N) protein plays an essential role in virion assembly via interactions with the large, positive-strand RNA viral genome and the carboxy-terminal endodomain of the membrane protein (M). To learn about the functions of N protein domains in the coronavirus mouse hepatitis virus (MHV), we replaced the MHV N gene with its counterpart from the closely related bovine coronavirus (BCoV). The resulting viral mutant was severely defective, even though individual domains of the N protein responsible for N-RNA, N-M, or N-N interactions were completely interchangeable between BCoV and MHV. The lesion in the BCoV N substitution mutant could be compensated for by reverting mutations in the central, serine- and arginine-rich (SR) domain of the N protein. Surprisingly, a second class of reverting mutations were mapped to the amino terminus of a replicase subunit, nonstructural protein 3 (nsp3). A similarly defective MHV N mutant bearing an insertion of the SR region from the severe acute respiratory syndrome coronavirus N protein was rescued by the same two classes of reverting mutations. Our genetic results were corroborated by the demonstration that the expressed amino-terminal segment of nsp3 bound selectively to N protein from infected cells, and this interaction was RNA independent. Moreover, we found a direct correlation between the N-nsp3 interaction and the ability of N protein to stimulate the infectivity of transfected MHV genomic RNA (gRNA). Our results suggest a role for this previously unknown N-nsp3 interaction in the localization of genomic RNA to the replicase complex at an early stage of infection.