Proteomics analysis unravels the functional repertoire of coronavirus nonstructural protein 3

Identification of Three Novel Linear B-Cell Epitopes in Non-Structural Protein 3 of Porcine Epidemic Diarrhea Virus Using Monoclonal Antibodies

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic swine coronavirus that causes diarrhea and high mortality in piglets, resulting in significant economic losses within the global swine industry. Nonstructural protein 3 (Nsp3) is the largest in coronavirus, playing critical roles in viral replication, such as the processing of polyproteins and the formation of replication-transcription complexes (RTCs). In this study, three monoclonal antibodies (mAbs), 7G4, 5A3, and 2D7, targeting PEDV Nsp3 were successfully generated, and three distinct linear B-cell epitopes were identified within these mAbs by using Western blotting analysis with 24 truncations of Nsp3. The epitope against 7G4 was located on amino acids 31-TISQDLLDVE-40, the epitope against 5A3 was found on amino acids 141-LGIVDDPAMG-150, and the epitope against 2D7 was situated on amino acids 282-FYDAAMAIDG-291. Intriguingly, the epitope 31-TISQDLLDVE-40 recognized by the mAb 7G4 appears to be a critical B-cell linear epitope due to its high antigenic index and exposed location on the surface of Nsp3 protein. In addition, bioinformatics analysis unveiled that these three epitopes were highly conserved in most genotypes of PEDV. These findings present the first characterization of three novel linear B-cell epitopes in the Nsp3 protein of PEDV and provide potential tools of mAbs for identifying host proteins that may facilitate viral infection.

Human Challenge Studies with Coronaviruses Old and New

Coronavirus infections have been known to cause disease in animals since as early as the 1920s. However, only seven coronaviruses capable of causing human disease have been identified thus far. These Human Coronaviruses (HCoVs) include the causes of the common cold, but more recent coronaviruses that have emerged (i.e. SARS-CoV, MERS-CoV and SARS-CoV-2) are associated with much greater morbidity and mortality. HCoVs have been relatively under-studied compared to other common respiratory infections, as historically they have presented with mild symptoms. This has led to a relatively limited understanding of their animal reservoirs, transmission and determinants of immune protection. To address this, human infection challenge studies with HCoVs have been performed that enable a detailed clinical and immunological analysis of the host response at specific time points under controlled conditions with standardised viral inocula. Until recently, all such human challenge studies were conducted with common cold HCoVs, with the study of SARS-CoV and MERS-CoV unacceptable due to their greater pathogenicity. However, with the emergence of SARS-CoV-2 and the COVID-19 pandemic during which severe outcomes in young healthy adults have been rare, human challenge studies with SARS-CoV-2 are now being developed. Two SARS-CoV-2 human challenge studies in the UK studying individuals with and without pre-existing immunity are underway. As well as providing a platform for testing of antivirals and vaccines, such studies will be critical for understanding the factors associated with susceptibility to SARS-CoV-2 infection and thus developing improved strategies to tackle the current as well as future HCoV pandemics. Here, we summarise the major questions about protection and pathogenesis in HCoV infection that human infection challenge studies have attempted to answer historically, as well as the knowledge gaps that aim to be addressed with contemporary models.

Investigation of the individual genetic evolution of SARS-CoV-2 in a small cluster during the rapid spread of the BF.5 lineage in Tokyo, Japan

There has been a decreasing trend in new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) cases and fatalities worldwide. The virus has been evolving, indicating the potential emergence of new variants and uncertainties. These challenges necessitate continued efforts in disease control and mitigation strategies. We investigated a small cluster of SARS-CoV-2 Omicron variant infections containing a common set of genomic mutations, which provided a valuable model for investigating the transmission mechanism of genetic alterations. We conducted a study at a medical center in Japan during the Omicron surge (sub-lineage BA.5), sequencing the entire SARS-CoV-2 genomes from infected individuals and evaluating the phylogenetic tree and haplotype network among the variants. We compared the mutations present in each strain within the BA.5 strain, TKYnat2317, which was first identified in Tokyo, Japan. From June 29th to July 4th 2022, nine healthcare workers (HCWs) tested positive for SARS-CoV-2 by real-time PCR. During the same period, five patients also tested positive by real-time PCR. Whole genome sequencing revealed that the infected patients belonged to either the isolated BA.2 or BA.5 sub-lineage, while the healthcare worker infections were classified as BF.5. The phylogenetic tree and haplotype network clearly showed the specificity and similarity of the HCW cluster. We identified 12 common mutations in the cluster, including I110V in nonstructural protein 4 (nsp4), A1020S in the Spike protein, and H47Y in ORF7a, compared to the BA.5 reference. Additionally, one case had the extra nucleotide-deletion mutation I27* in ORF10, and low frequencies of genetic alterations were also found in certain instances. The results of genome sequencing showed that the nine HCWs shared a set of genetic mutations, indicating transmission within the cluster. Minor mutations observed in five HCW individuals suggested the emergence of new virus variants. Five amino acid substitutions occurred in nsp3, which could potentially affect virus replication or immune escape. Intra-host evolution also generated additional mutations. The cluster exhibited a mild disease course, with individuals in this case, recovering without requiring any medical treatments. Further investigation is needed to understand the relationship between the genetic evolution of the virus and the symptoms.

Proteomic profiling of purified avian leukosis virus subgroup J particles

While the presence of host cell proteins in virions and their role in viral life cycles have been demonstrated in various viruses, such characteristics have remained largely unknown in avian leukosis virus (ALV). To investigate whether this is the case in ALV, we purified high-integrity and high-purity virions from the avian leukosis virus subgroup J (ALV-J) and subjected them to proteome analysis using nano LC-MS/MS. This analysis identified 53 cellular proteins that are incorporated into mature ALV-J virions, and we verified the reliability of the packaged cellular proteins through subtilisin digestion and immunoblot analysis. Functional annotation revealed the potential functions of these proteins in the viral life cycle and tumorigenesis. Overall, our findings have important implications for understanding the interaction between ALV-J and its host, and provide new insights into the cellular requirements that define ALV-J infection.

Nsp3-N interactions are critical for SARS-CoV-2 fitness and virulence

SARS-CoV-2, the causative agent of COVID-19 encodes at least 16 nonstructural proteins of variably understood function. Nsp3, the largest nonstructural protein contains several domains, including a SARS-unique domain (SUD), which occurs only in Sarbecovirus. The SUD has a role in preferentially enhancing viral translation. During isolation of mouse-adapted SARS-CoV-2, we isolated an attenuated virus that contained a single mutation in a linker region of nsp3 (nsp3-S676T). The S676T mutation decreased virus replication in cultured cells and primary human cells and in mice. Nsp3-S676T alleviated the SUD translational enhancing ability by decreasing the interaction between two translation factors, Paip1 and PABP1. We also identified a compensatory mutation in the nucleocapsid (N) protein (N-S194L) that restored the virulent phenotype, without directly binding to SUD. Together, these results reveal an aspect of nsp3-N interactions, which impact both SARS-CoV-2 replication and, consequently, pathogenesis.

A single inactivating amino acid change in the SARS-CoV-2 NSP3 Mac1 domain attenuates viral replication in vivo

Despite unprecedented efforts, our therapeutic arsenal against SARS-CoV-2 remains limited. The conserved macrodomain 1 (Mac1) in NSP3 is an enzyme exhibiting ADP-ribosylhydrolase activity and a possible drug target. To determine the role of Mac1 catalytic activity in viral replication, we generated recombinant viruses and replicons encoding a catalytically inactive NSP3 Mac1 domain by mutating a critical asparagine in the active site. While substitution to alanine (N40A) reduced catalytic activity by ~10-fold, mutations to aspartic acid (N40D) reduced activity by ~100-fold relative to wild-type. Importantly, the N40A mutation rendered Mac1 unstable in vitro and lowered expression levels in bacterial and mammalian cells. When incorporated into SARS-CoV-2 molecular clones, the N40D mutant only modestly affected viral fitness in immortalized cell lines, but reduced viral replication in human airway organoids by 10-fold. In mice, the N40D mutant replicated at >1000-fold lower levels compared to the wild-type virus while inducing a robust interferon response; all animals infected with the mutant virus survived infection. Our data validate the critical role of SARS-CoV-2 NSP3 Mac1 catalytic activity in viral replication and as a promising therapeutic target to develop antivirals.

Novel Mode of nanoLuciferase Packaging in SARS-CoV-2 Virions and VLPs Provides Versatile Reporters for Virus Production

SARS-CoV-2 is a positive-strand RNA virus in the Coronaviridae family that is responsible for morbidity and mortality worldwide. To better understand the molecular pathways leading to SARS-CoV-2 virus assembly, we examined a virus-like particle (VLP) system co-expressing all structural proteins together with an mRNA reporter encoding nanoLuciferase (herein nLuc). Surprisingly, the 19 kDa nLuc protein itself was encapsidated into VLPs, providing a better reporter than nLuc mRNA itself. Strikingly, infecting nLuc-expressing cells with the SARS-CoV-2, NL63 or OC43 coronaviruses yielded virions containing packaged nLuc that served to report viral production. In contrast, infection with the flaviviruses, dengue or Zika, did not lead to nLuc packaging and secretion. A panel of reporter protein variants revealed that the packaging is size-limited and requires cytoplasmic expression, indicating that the large virion of coronaviruses can encaspidate a small cytoplasmic reporter protein. Our findings open the way for powerful new approaches to measure coronavirus particle production, egress and viral entry mechanisms.

A single inactivating amino acid change in the SARS-CoV-2 NSP3 Mac1 domain attenuates viral replication and pathogenesis in vivo

Despite unprecedented efforts, our therapeutic arsenal against SARS-CoV-2 remains limited. The conserved macrodomain 1 (Mac1) in NSP3 is an enzyme exhibiting ADP-ribosylhydrolase activity and a possible drug target. To determine the therapeutic potential of Mac1 inhibition, we generated recombinant viruses and replicons encoding a catalytically inactive NSP3 Mac1 domain by mutating a critical asparagine in the active site. While substitution to alanine (N40A) reduced catalytic activity by ~10-fold, mutations to aspartic acid (N40D) reduced activity by ~100-fold relative to wildtype. Importantly, the N40A mutation rendered Mac1 unstable in vitro and lowered expression levels in bacterial and mammalian cells. When incorporated into SARS-CoV-2 molecular clones, the N40D mutant only modestly affected viral fitness in immortalized cell lines, but reduced viral replication in human airway organoids by 10-fold. In mice, N40D replicated at >1000-fold lower levels compared to the wildtype virus while inducing a robust interferon response; all animals infected with the mutant virus survived infection and showed no signs of lung pathology. Our data validate the SARS-CoV-2 NSP3 Mac1 domain as a critical viral pathogenesis factor and a promising target to develop antivirals.

SARS-CoV-2 SUD2 and Nsp5 Conspire to Boost Apoptosis of Respiratory Epithelial Cells via an Augmented Interaction with the G-Quadruplex of BclII

The molecular mechanisms underlying how SUD2 recruits other proteins of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to exert its G-quadruplex (G4)-dependent pathogenic function is unknown. Herein, Nsp5 was singled out as a binding partner of the SUD2-N+M domains (SUD2core) with high affinity, through the surface located crossing these two domains. Biochemical and fluorescent assays demonstrated that this complex also formed in the nucleus of living host cells. Moreover, the SUD2core-Nsp5 complex displayed significantly enhanced selective binding affinity for the G4 structure in the BclII promoter than did SUD2core alone. This increased stability exhibited by the tertiary complex was rationalized by AlphaFold2 and molecular dynamics analysis. In line with these molecular interactions, downregulation of BclII and subsequent augmented apoptosis of respiratory cells were both observed. These results provide novel information and a new avenue to explore therapeutic strategies targeting SARS-CoV-2. IMPORTANCE SUD2, a unique protein domain closely related to the pathogenesis of SARS-CoV-2, has been reported to bind with the G-quadruplex (G4), a special noncanonical DNA structure endowed with important functions in regulating gene expression. However, the interacting partner of SUD2, among other SARS-CoV-2 Nsps, and the resulting functional consequences remain unknown. Here, a stable complex formed between SUD2 and Nsp5 was fully characterized both in vitro and in host cells. Moreover, this complex had a significantly enhanced binding affinity specifically targeting the Bcl2G4 in the promoter region of the antiapoptotic gene BclII, compared with SUD2 alone. In respiratory epithelial cells, the SUD2-Nsp5 complex promoted BclII-mediated apoptosis in a G4-dependent manner. These results reveal fresh information about matched multicomponent interactions, which can be parlayed to develop new therapeutics for future relevant viral disease.

Molecular mechanisms of human coronavirus NL63 infection and replication

Human coronavirus NL63 (HCoV-NL63) is spread globally, causing upper and lower respiratory tract infections mainly in young children. HCoV-NL63 shares a host receptor (ACE2) with severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2 but, unlike them, HCoV-NL63 primarily develops into self-limiting mild to moderate respiratory disease. Although with different efficiency, both HCoV-NL63 and SARS-like CoVs infect ciliated respiratory cells using ACE2 as receptor for binding and cell entry. Working with SARS-like CoVs require access to BSL-3 facilities, while HCoV-NL63 research can be performed at BSL-2 laboratories. Thus, HCoV-NL63 could be used as a safer surrogate for comparative studies on receptor dynamics, infectivity and virus replication, disease mechanism, and potential therapeutic interventions against SARS-like CoVs. This prompted us to review the current knowledge on the infection mechanism and replication of HCoV-NL63. Specifically, after a brief overview on the taxonomy, genomic organization and virus structure, this review compiles the current HCoV-NL63-related research in virus entry and replication mechanism, including virus attachment, endocytosis, genome translation, and replication and transcription. Furthermore, we reviewed cumulative knowledge on the susceptibility of different cells to HCoV-NL63 infection in vitro, which is essential for successful virus isolation and propagation, and contribute to address different scientific questions from basic science to the development and assessment of diagnostic tools, and antiviral therapies. Finally, we discussed different antiviral strategies that have been explored to suppress replication of HCoV-NL63, and other related human coronaviruses, by either targeting the virus or enhancing host antiviral mechanisms.

Crystal structure of the CoV-Y domain of SARS-CoV-2 nonstructural protein 3

Replication of the coronavirus genome starts with the formation of viral RNA-containing double-membrane vesicles (DMV) following viral entry into the host cell. The multi-domain nonstructural protein 3 (nsp3) is the largest protein encoded by the known coronavirus genome and serves as a central component of the viral replication and transcription machinery. Previous studies demonstrated that the highly-conserved C-terminal region of nsp3 is essential for subcellular membrane rearrangement, yet the underlying mechanisms remain elusive. Here we report the crystal structure of the CoV-Y domain, the most C-terminal domain of the SARS-CoV-2 nsp3, at 2.4 Å-resolution. CoV-Y adopts a previously uncharacterized V-shaped fold featuring three distinct subdomains. Sequence alignment and structure prediction suggest that this fold is likely shared by the CoV-Y domains from closely related nsp3 homologs. NMR-based fragment screening combined with molecular docking identifies surface cavities in CoV-Y for interaction with potential ligands and other nsps. These studies provide the first structural view on a complete nsp3 CoV-Y domain, and the molecular framework for understanding the architecture, assembly and function of the nsp3 C-terminal domains in coronavirus replication. Our work illuminates nsp3 as a potential target for therapeutic interventions to aid in the on-going battle against the COVID-19 pandemic and diseases caused by other coronaviruses.

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.

Modeling of SARS-CoV-2 Virus Proteins: Implications on Its Proteome

COronaVIrus Disease 19 (COVID-19) is a severe acute respiratory syndrome (SARS) caused by a group of beta coronaviruses, SARS-CoV-2. The SARS-CoV-2 virus is similar to previous SARS- and MERS-causing strains and has infected nearly six hundred and fifty million people all over the globe, while the death toll has crossed the six million mark (as of December, 2022). In this chapter, we look at how computational modeling approaches of the viral proteins could help us understand the various processes in the viral life cycle inside the host, an understanding of which might provide key insights in mitigating this and future threats. This understanding helps us identify key targets for the purpose of drug discovery and vaccine development.

Origin of New Lineages by Recombination and Mutation in Avian Infectious Bronchitis Virus from South America

The gammacoronavirus avian infectious bronchitis virus (IBV) is a highly contagious respiratory pathogen of primary economic importance to the global poultry industry. Two IBV lineages (GI-11 and GI-16) have been widely circulating for decades in South America. GI-11 is endemic to South America, and the GI-16 is globally distributed. We obtained full-length IBV genomes from Argentine and Uruguayan farms using Illumina sequencing. Genomes of the GI-11 and GI-16 lineages from Argentina and Uruguay differ in part of the spike coding region. The remaining genome regions are similar to the Chinese and Italian strains of the GI-16 lineage that emerged in Asia or Europe in the 1970s. Our findings support that the indigenous GI-11 strains recombine extensively with the invasive GI-16 strains. During the recombination process, GI-11 acquired most of the sequences of the GI-16, retaining the original S1 sequence. GI-11 strains with recombinant genomes are circulating forms that underwent further local evolution. The current IBV scenario in South America includes the GI-16 lineage, recombinant GI-11 strains sharing high similarity with GI-16 outside S1, and Brazilian GI-11 strains with a divergent genomic background. There is also sporadic recombinant in the GI-11 and GI-16 lineages among vaccine and field strains. Our findings exemplified the ability of IBV to generate emergent lineage by using the S gene in different genomic backgrounds. This unique example of recombinational microevolution underscores the genomic plasticity of IBV in South America.

Unique mutations in SARS-CoV-2 Omicron subvariants' non-spike proteins: Potential impacts on viral pathogenesis and host immune evasion

SARS-CoV-2 is the causative agent behind the ongoing COVID-19 pandemic. This virus is a cumulative outcome of mutations, leading to frequent emergence of new variants and their subvariants. Some of them are a matter of high concern, while others are variants of interest for studying the mutational effect. The major five variants of concern (VOCs) are Alpha (B.1.1.7), Beta (B.1.315), Gamma (P.1), Delta (B.1.617.2), and Omicron (B.1.1.529.*/BA.*). Omicron itself has >100 subvariants at present, among which BA.1 (21K), BA.2 (21L), BA.4 (22A), BA.5 (22B), and BA.2.12.1 (22C) are the dominant ones. Undoubtedly, these variants and sometimes their progeny subvariants have significant differences in their spike region that impart them the unique properties they harbor. But alongside, the mutations in their non-spike regions could also be responsible elements behind their characteristics, such as replication time, virulence, survival, host immune evasion, and such. There exists a probability that these mutations of non-spike proteins may also impart epistatic effects that are yet to be brought to light. The focus of this review encompasses the non-spike mutations of Omicron, especially in its widely circulating subvariants (BA.1, BA.2, BA.4, BA.5, and BA.2.12.1). The mutations such as in NSP3, NSP6, NSP13, M protein, ORF7b, and ORF9b are mentioned few of all, which might have led to the varying properties, including growth advantages, higher transmission rate, lower infectivity, and most importantly better host immune evasion through natural killer cell inactivation, autophagosome-lysosome fusion prevention, host protein synthesis disruption, and so on. This aspect of Omicron subvariants has not yet been explored. Further study of alteration of expression or interaction profile of these non-spike mutations bearing proteins, if present, can add a great deal of knowledge to the current understanding of the viral properties and thus effective prevention strategies.

The zinc proteome of SARS-CoV-2

Zinc is an essential element for human health. Among its many functions, zinc(II) modulates the immune response to infections and, at high concentrations or in the presence of ionophores, inhibits the replication of various RNA viruses. Structural biology studies on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) revealed that zinc(II) is the most common metal ion that binds to viral proteins. However, the number of zinc(II)-binding sites identified by experimental methods is far from exhaustive, as metal ions may be lost during protein purification protocols. To better define the zinc(II)-binding proteome of coronavirus, we leveraged the wealth of deposited structural data and state-of-the-art bioinformatics methods. Through this in silico approach, 15 experimental zinc(II) sites were identified and a further 22 were predicted in Spike, open reading frame (ORF)3a/d, ORF8, and several nonstructural proteins, highlighting an essential role of zinc(II) in viral replication. Furthermore, the structural relationships between viral and eukaryotic sites (typically zinc fingers) indicate that SARS-CoV-2 can compete with human proteins for zinc(II) binding. Given the double-edged effect of zinc(II) ions, both essential and toxic to coronavirus, only the complete elucidation of the structural and regulatory zinc(II)-binding sites can guide selective antiviral strategies based on zinc supplementation.

Whole-body metabolic modelling predicts isoleucine dependency of SARS-CoV-2 replication

We aimed at investigating host-virus co-metabolism during SARS-CoV-2 infection. Therefore, we extended comprehensive sex-specific, whole-body organ resolved models of human metabolism with the necessary reactions to replicate SARS-CoV-2 in the lung as well as selected peripheral organs. Using this comprehensive host-virus model, we obtained the following key results: 1. The predicted maximal possible virus shedding rate was limited by isoleucine availability. 2. The supported initial viral load depended on the increase in CD4+ T-cells, consistent with the literature. 3. During viral infection, the whole-body metabolism changed including the blood metabolome, which agreed well with metabolomic studies from COVID-19 patients and healthy controls. 4. The virus shedding rate could be reduced by either inhibition of the guanylate kinase 1 or availability of amino acids, e.g., in the diet. 5. The virus variants differed in their maximal possible virus shedding rates, which could be inversely linked to isoleucine occurrences in the sequences. Taken together, this study presents the metabolic crosstalk between host and virus and emphasises the role of amino acid metabolism during SARS-CoV-2 infection, in particular of isoleucine. As such, it provides an example of how computational modelling can complement more canonical approaches to gain insight into host-virus crosstalk and to identify potential therapeutic strategies.

Endomembrane remodeling in SARS-CoV-2 infection

During severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, the viral proteins intimately interact with host factors to remodel the endomembrane system at various steps of the viral lifecycle. The entry of SARS-CoV-2 can be mediated by endocytosis-mediated internalization. Virus-containing endosomes then fuse with lysosomes, in which the viral S protein is cleaved to trigger membrane fusion. Double-membrane vesicles generated from the ER serve as platforms for viral replication and transcription. Virions are assembled at the ER-Golgi intermediate compartment and released through the secretory pathway and/or lysosome-mediated exocytosis. In this review, we will focus on how SARS-CoV-2 viral proteins collaborate with host factors to remodel the endomembrane system for viral entry, replication, assembly and egress. We will also describe how viral proteins hijack the host cell surveillance system-the autophagic degradation pathway-to evade destruction and benefit virus production. Finally, potential antiviral therapies targeting the host cell endomembrane system will be discussed.

Identification of intrinsically disorder regions in non-structural proteins of SARS-CoV-2: New insights into drug and vaccine resistance

The outbreak of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) emerged in December 2019 and caused coronavirus disease 2019 (COVID-19), which causes pneumonia and severe acute respiratory distress syndrome. It is a highly infectious pathogen that promptly spread. Like other beta coronaviruses, SARS-CoV-2 encodes some non-structural proteins (NSPs), playing crucial roles in viral transcription and replication. NSPs likely have essential roles in viral pathogenesis by manipulating many cellular processes. We performed a sequence-based analysis of NSPs to get insights into their intrinsic disorders, and their functions in viral replication were annotated and discussed in detail. Here, we provide newer insights into the structurally disordered regions of SARS-CoV-2 NSPs. Our analysis reveals that the SARS-CoV-2 proteome has a chunk of the disordered region that might be responsible for increasing its virulence. In addition, mutations in these regions are presumably responsible for drug and vaccine resistance. These findings suggested that the structurally disordered regions of SARS-CoV-2 NSPs might be invulnerable in COVID-19.

NMR study of macro domains (MDs) from betacoronavirus: backbone resonance assignments of SARS-CoV and MERS-CoV MDs in the free and the ADPr-bound state

SARS-CoV and MERS-CoV Macro Domains (MDs) exhibit topological and conformational features that resemble the nsP3b macro (or "X") domain of SARS-CoV-2. Indeed, all the three domains (SARS-CoV-2, SARS-CoV and MERS-CoV MDs) fold in a three-layer α/β/α sandwich structure, as reported by crystallographic structural investigation of SARS-CoV MD and MERS-CoV MD. These viral MDs are able to bind ADP-ribose as many other MDs from different kingdoms. They have been characterized also as de-ADP-ribosylating enzymes. For this reason, these viral macrodomains recently emerged as important drug targets since they can counteract antiviral ADP-ribosylation mediated by poly-ADP-ribose polymerase (PARPs). Even in presence of the 3D structures of SARS-CoV MD and of MERS-CoV MD, we report herein the almost complete NMR backbone (¹H, ¹³C, ¹⁵N) of SARS-CoV MD and MERS-CoV proteins in the free and ADPr bound forms, and the NMR chemical shift-based prediction of their secondary structure elements. These NMR data will help to further understanding of the atomic-level conformational dynamics of these proteins and will allow an extensive screening of small molecules as potential antiviral drugs.

CRESSP: a comprehensive pipeline for prediction of immunopathogenic SARS-CoV-2 epitopes using structural properties of proteins

The development of autoimmune diseases following SARS-CoV-2 infection, including multisystem inflammatory syndrome, has been reported, and several mechanisms have been suggested, including molecular mimicry. We developed a scalable, comparative immunoinformatics pipeline called cross-reactive-epitope-search-using-structural-properties-of-proteins (CRESSP) to identify cross-reactive epitopes between a collection of SARS-CoV-2 proteomes and the human proteome using the structural properties of the proteins. Overall, by searching 4 911 245 proteins from 196 352 SARS-CoV-2 genomes, we identified 133 and 648 human proteins harboring potential cross-reactive B-cell and CD8+ T-cell epitopes, respectively. To demonstrate the robustness of our pipeline, we predicted the cross-reactive epitopes of coronavirus spike proteins, which were recognized by known cross-neutralizing antibodies. Using single-cell expression data, we identified PARP14 as a potential target of intermolecular epitope spreading between the virus and human proteins. Finally, we developed a web application (https://ahs2202.github.io/3M/) to interactively visualize our results. We also made our pipeline available as an open-source CRESSP package (https://pypi.org/project/cressp/), which can analyze any two proteomes of interest to identify potentially cross-reactive epitopes between the proteomes. Overall, our immunoinformatic resources provide a foundation for the investigation of molecular mimicry in the pathogenesis of autoimmune and chronic inflammatory diseases following COVID-19.

Targeting SARS-CoV-2 Proteases and Polymerase for COVID-19 Treatment: State of the Art and Future Opportunities

The newly emerged coronavirus, called SARS-CoV-2, is the causing pathogen of pandemic COVID-19. The identification of drugs to treat COVID-19 and other coronavirus diseases is an urgent global need, thus different strategies targeting either virus or host cell are still under investigation. Direct-acting agents, targeting protease and polymerase functionalities, represent a milestone in antiviral therapy. The 3C-like (or Main) protease (3CLpro) and the nsp12 RNA-dependent RNA-polymerase (RdRp) are the best characterized SARS-CoV-2 targets and show the highest degree of conservation across coronaviruses fostering the identification of broad-spectrum inhibitors. Coronaviruses also possess a papain-like protease, another essential enzyme, still poorly characterized and not equally conserved, limiting the identification of broad-spectrum agents. Herein, we provide an exhaustive comparative analysis of SARS-CoV-2 proteases and RdRp with respect to other coronavirus homologues. Moreover, we highlight the most promising inhibitors of these proteins reported so far, including the possible strategies for their further development.

Targeting SARS-CoV-2 Proteases and Polymerase for COVID-19 Treatment: State of the Art and Future Opportunities

The newly emerged coronavirus, called SARS-CoV-2, is the causing pathogen of pandemic COVID-19. The identification of drugs to treat COVID-19 and other coronavirus diseases is an urgent global need, thus different strategies targeting either virus or host cell are still under investigation. Direct-acting agents, targeting protease and polymerase functionalities, represent a milestone in antiviral therapy. The 3C-like (or Main) protease (3CL^pro) and the nsp12 RNA-dependent RNA-polymerase (RdRp) are the best characterized SARS-CoV-2 targets and show the highest degree of conservation across coronaviruses fostering the identification of broad-spectrum inhibitors. Coronaviruses also possess a papain-like protease, another essential enzyme, still poorly characterized and not equally conserved, limiting the identification of broad-spectrum agents. Herein, we provide an exhaustive comparative analysis of SARS-CoV-2 proteases and RdRp with respect to other coronavirus homologues. Moreover, we highlight the most promising inhibitors of these proteins reported so far, including the possible strategies for their further development.

A Defective Viral Particle Approach to COVID-19

The novel coronavirus SARS-CoV-2 has caused a pandemic resulting in millions of deaths worldwide. While multiple vaccines have been developed, insufficient vaccination combined with adaptive mutations create uncertainty for the future. Here, we discuss novel strategies to control COVID-19 relying on Defective Interfering Particles (DIPs) and related particles that arise naturally during an infection. Our intention is to encourage and to provide the basis for the implementation of such strategies by multi-disciplinary teams. We therefore provide an overview of SARS-CoV-2 for a multi-disciplinary readership that is specifically tailored to these strategies, we identify potential targets based on the current knowledge of the properties and functions of coronaviruses, and we propose specific strategies to engineer DIPs and other interfering or therapeutic nanoparticles.

Intra-Host SARS-CoV-2 Evolution in the Gut of Mucosally-Infected Chlorocebus aethiops (African Green Monkeys)

In recent months, several SARS-CoV-2 variants have emerged that enhance transmissibility and escape host humoral immunity. Hence, the tracking of viral evolutionary trajectories is clearly of great importance. Little is known about SARS-CoV-2 evolution in nonhuman primate models used to test vaccines and therapies and to model human disease. Viral RNA was sequenced from rectal swabs from Chlorocebus aethiops (African green monkeys) after experimental respiratory SARS-CoV-2 infection. Two distinct patterns of viral evolution were identified that were shared between all collected samples. First, mutations in the furin cleavage site that were initially present in the virus as a consequence of VeroE6 cell culture adaptation were not detected in viral RNA recovered in rectal swabs, confirming the necessity of this motif for viral infection in vivo. Three amino acid changes were also identified; ORF 1a S2103F, and spike D215G and H655Y, which were detected in rectal swabs from all sampled animals. These findings are demonstrative of intra-host SARS-CoV-2 evolution and may identify a host-adapted variant of SARS-CoV-2 that would be useful in future primate models involving SARS-CoV-2 infection.

Analysis of a crucial interaction between the coronavirus nucleocapsid protein and the major membrane-bound subunit of the viral replicase-transcriptase complex

The coronavirus nucleocapsid (N) protein comprises two RNA-binding domains connected by a central spacer, which contains a serine- and arginine-rich (SR) region. The SR region engages the largest subunit of the viral replicase-transcriptase, nonstructural protein 3 (nsp3), in an interaction that is essential for efficient initiation of infection by genomic RNA. We carried out an extensive genetic analysis of the SR region of the N protein of mouse hepatitis virus in order to more precisely define its role in RNA synthesis. We further examined the N-nsp3 interaction through construction of nsp3 mutants and by creation of an interspecies N protein chimera. Our results indicate a role for the central spacer as an interaction hub of the N molecule that is partially regulated by phosphorylation. These findings are discussed in relation to the recent discovery that nsp3 forms a molecular pore in the double-membrane vesicles that sequester the coronavirus replicase-transcriptase.

VLP-Based COVID-19 Vaccines: An Adaptable Technology against the Threat of New Variants

Virus-like particles (VLPs) are a versatile, safe, and highly immunogenic vaccine platform. Recently, there are developmental vaccines targeting SARS-CoV-2, the causative agent of COVID-19. The COVID-19 pandemic affected humanity worldwide, bringing out incomputable human and financial losses. The race for better, more efficacious vaccines is happening almost simultaneously as the virus increasingly produces variants of concern (VOCs). The VOCs Alpha, Beta, Gamma, and Delta share common mutations mainly in the spike receptor-binding domain (RBD), demonstrating convergent evolution, associated with increased transmissibility and immune evasion. Thus, the identification and understanding of these mutations is crucial for the production of new, optimized vaccines. The use of a very flexible vaccine platform in COVID-19 vaccine development is an important feature that cannot be ignored. Incorporating the spike protein and its variations into VLP vaccines is a desirable strategy as the morphology and size of VLPs allows for better presentation of several different antigens. Furthermore, VLPs elicit robust humoral and cellular immune responses, which are safe, and have been studied not only against SARS-CoV-2 but against other coronaviruses as well. Here, we describe the recent advances and improvements in vaccine development using VLP technology.

An overview of SARS-COV-2 epidemiology, mutant variants, vaccines, and management strategies

BACKGROUND

Over the last two decades, humanity has observed the extraordinary anomaly caused by novel, weird coronavirus strains, such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). As the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus has made its entry into the world, it has dramatically affected life in every domain by continuously producing new variants. The vaccine development is an ongoing process, although some vaccines got marketed. The big challenge is now whether the vaccine candidates can provide long-lasting protection or prevention against mutant variants.

METHODS

The information was gathered from various journals, electronic searches via Internet-based information such as PubMed, Google Scholar, Science Direct, online electronic journals, WHO landscape, world meters, WHO website, and News.

RESULTS

This review will present and discuss some coronavirus disease 19 (COVID-19) related aspects including: the pathophysiology, epidemiology, mutant variants vaccine candidates, vaccine efficacy, and management strategies. Due to the high death rate, continuous spread, an inadequate workforce, lack of required therapeutics, and incomplete understanding of the viral strain, it becomes crucial to build the knowledge of its biological characteristics and make available the rapid diagnostic and vital therapeutic machinery for the combat and management of an infection.

CONCLUSION

The data summarizes current research on the COVID 19 infection and therapeutic interventions, which will direct future decision-making on the effort-worthy phases of the COVID 19 and the development of critical therapeutics. The only possible solution is the vaccine development targeting against all variant strains to halt its progress; the identified theoretical and practical knowledge can eliminate the gaps to improve a better understanding of the novel coronavirus structure and its design of a vaccine. In addition, to that the long-lasting protection is another challenging objective that need to be looked into.

Positive selection as a key player for SARS-CoV-2 pathogenicity: Insights into ORF1ab, S and E genes

The human β-coronavirus SARS-CoV-2 epidemic started in late December 2019 in Wuhan, China. It causes Covid-19 disease which has become pandemic. Each of the five-known human β-coronaviruses has four major structural proteins (E, M, N and S) and 16 non-structural proteins encoded by ORF1a and ORF1b together (ORF1ab) that are involved in virus pathogenicity and infectivity. Here, we performed detailed positive selection analyses for those six genes among the four previously known human β-coronaviruses and within 38 SARS-CoV-2 genomes to assess signatures of adaptive evolution using maximum likelihood approaches. Our results suggest that three genes (E, S and ORF1ab genes) are under strong signatures of positive selection among human β-coronavirus, influencing codons that are located in functional important protein domains. The E protein-coding gene showed signatures of positive selection in two sites, Asp 66 and Ser 68, located inside a putative transmembrane α-helical domain C-terminal part, which is preferentially composed by hydrophilic residues. Such Asp and Ser sites substitutions (hydrophilic residues) increase the stability of the transmembrane domain in SARS-CoV-2. Moreover, substitutions in the spike (S) protein S1 N-terminal domain have been found, all of them were located on the S protein surface, suggesting their importance in viral transmissibility and survival. Furthermore, evidence of strong positive selection was detected in three of the SARS-CoV-2 nonstructural proteins (NSP1, NSP3, NSP16), which are encoded by ORF1ab and play vital roles in suppressing host translation machinery, viral replication and transcription and inhibiting the host immune response. These results are insightful to assess the role of positive selection in the SARS-CoV-2 encoded proteins, which will allow to better understand the virulent pathogenicity of the virus and potentially identifying targets for drug or vaccine strategy design.

SARS-CoV-2 Nsp3 unique domain SUD interacts with guanine quadruplexes and G4-ligands inhibit this interaction

The multidomain non-structural protein 3 (Nsp3) is the largest protein encoded by coronavirus (CoV) genomes and several regions of this protein are essential for viral replication. Of note, SARS-CoV Nsp3 contains a SARS-Unique Domain (SUD), which can bind Guanine-rich non-canonical nucleic acid structures called G-quadruplexes (G4) and is essential for SARS-CoV replication. We show herein that the SARS-CoV-2 Nsp3 protein also contains a SUD domain that interacts with G4s. Indeed, interactions between SUD proteins and both DNA and RNA G4s were evidenced by G4 pull-down, Surface Plasmon Resonance and Homogenous Time Resolved Fluorescence. These interactions can be disrupted by mutations that prevent oligonucleotides from folding into G4 structures and, interestingly, by molecules known as specific ligands of these G4s. Structural models for these interactions are proposed and reveal significant differences with the crystallographic and modeled 3D structures of the SARS-CoV SUD-NM/G4 interaction. Altogether, our results pave the way for further studies on the role of SUD/G4 interactions during SARS-CoV-2 replication and the use of inhibitors of these interactions as potential antiviral compounds.

Plitidepsin: Mechanisms and Clinical Profile of a Promising Antiviral Agent against COVID-19

Current standard treatment of COVID-19 lacks in effective antiviral options. Plitidepsin, a cyclic depsipeptide authorized in Australia for patients with refractory multiple myeloma, has recently emerged as a candidate anti-SARS-CoV-2 agent. The aim of this review was to summarize current knowledge on plitidepsin's clinical profile, anti-tumour and anti-SARS-CoV-2 mechanisms and correlate this with available or anticipated, preclinical or clinical evidence on the drug's potential for COVID-19 treatment.PubMed, Scopus, CENTRAL, clinicaltrials.gov, medRxiv and bioRxiv databases were searched.Plitidepsinexerts its anti-tumour and antiviral properties primarily through acting on isoforms of the host cell's eukaryotic-translation-elongation-factor-1-alpha (eEF1A). Through inhibiting eEF1A and therefore translation of necessary viral proteins, it behaves as a "host-directed" anti-SARS-CoV-2 agent. In respect to its potent anti-SARS-CoV-2 properties, the drug has demonstrated superior ex vivo efficacy compared to other host-directed agents and remdesivir, and it might retain its antiviral effect against the more transmittable B.1.1.7 variant. Its well-studied safety profile, also in combination with dexamethasone, may accelerate its repurposing chances for COVID-19 treatment. Preliminary findings in hospitalized COVID-19 patients, have suggested potential safety and efficacy of plitidepsin, in terms of viral load reduction and clinical resolution. However, the still incomplete understanding of its exact integration into host cell-SARS-CoV-2 interactions, its intravenous administration exclusively purposing it for hospital settings the and precocity of clinical data are currently considered its chief deficits. A phase III trial is being planned to compare the plitidepsin-dexamethasone regimen to the current standard of care only in moderately affected hospitalized patients. Despite plitidepsin's preclinical efficacy, current clinical evidence is inadequate for its registration in COVID-19 patients.Therefore, multicentre trials on the drug's efficacy, potentially also studying populations of emerging SARS-CoV-2 lineages, are warranted.

Structure and Function of Major SARS-CoV-2 and SARS-CoV Proteins

SARS-CoV-2 virus, the causative agent of COVID-19 pandemic, has a genomic organization consisting of 16 nonstructural proteins (nsps), 4 structural proteins, and 9 accessory proteins. Relative of SARS-CoV-2, SARS-CoV, has genomic organization, which is very similar. In this article, the function and structure of the proteins of SARS-CoV-2 and SARS-CoV are described in great detail. The nsps are expressed as a single or two polyproteins, which are then cleaved into individual proteins using two proteases of the virus, a chymotrypsin-like protease and a papain-like protease. The released proteins serve as centers of virus replication and transcription. Some of these nsps modulate the host’s translation and immune systems, while others help the virus evade the host immune system. Some of the nsps help form replication-transcription complex at double-membrane vesicles. Others, including one RNA-dependent RNA polymerase and one exonuclease, help in the polymerization of newly synthesized RNA of the virus and help minimize the mutation rate by proofreading. After synthesis of the viral RNA, it gets capped. The capping consists of adding GMP and a methylation mark, called cap 0 and additionally adding a methyl group to the terminal ribose called cap1. Capping is accomplished with the help of a helicase, which also helps remove a phosphate, two methyltransferases, and a scaffolding factor. Among the structural proteins, S protein forms the receptor of the virus, which latches on the angiotensin-converting enzyme 2 receptor of the host and N protein binds and protects the genomic RNA of the virus. The accessory proteins found in these viruses are small proteins with immune modulatory roles. Besides functions of these proteins, solved X-ray and cryogenic electron microscopy structures related to the function of the proteins along with comparisons to other coronavirus homologs have been described in the article. Finally, the rate of mutation of SARS-CoV-2 residues of the proteome during the 2020 pandemic has been described. Some proteins are mutated more often than other proteins, but the significance of these mutation rates is not fully understood.

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.

An Immunoinformatics Approach for SARS-CoV-2 in Latam Populations and Multi-Epitope Vaccine Candidate Directed towards the World's Population

The coronavirus pandemic is a major public health crisis affecting global health systems with dire socioeconomic consequences, especially in vulnerable regions such as Latin America (LATAM). There is an urgent need for a vaccine to help control contagion, reduce mortality and alleviate social costs. In this study, we propose a rational multi-epitope candidate vaccine against SARS-CoV-2. Using bioinformatics, we constructed a library of potential vaccine peptides, based on the affinity of the most common major human histocompatibility complex (HLA) I and II molecules in the LATAM population to predict immunological complexes among antigenic, non-toxic and non-allergenic peptides extracted from the conserved regions of 92 proteomes. Although HLA-C, had the greatest antigenic peptide capacity from SARS-CoV-2, HLA-B and HLA-A, could be more relevant based on COVID-19 risk of infection in LATAM countries. We also used three-dimensional structures of SARS-CoV-2 proteins to identify potential regions for antibody production. The best HLA-I and II predictions (with increased coverage in common alleles and regions evoking B lymphocyte responses) were grouped into an optimized final multi-epitope construct containing the adjuvants Beta defensin-3, TpD, and PADRE, which are recognized for invoking a safe and specific immune response. Finally, we used Molecular Dynamics to identify the multi-epitope construct which may be a stable target for TLR-4/MD-2. This would prove to be safe and provide the physicochemical requirements for conducting experimental tests around the world.

The human pandemic coronaviruses on the show: The spike glycoprotein as the main actor in the coronaviruses play

Three coronaviruses (CoVs) have threatened the world population by causing outbreaks in the last two decades. In late 2019, the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) emerged and caused the coronaviruses to disease 2019 (COVID-19), leading to the ongoing global outbreak. The other pandemic coronaviruses, SARS-CoV and Middle East respiratory syndrome CoV (MERS-CoV), share a considerable level of similarities at genomic and protein levels. However, the differences between them lead to distinct behaviors. These differences result from the accumulation of mutations in the sequence and structure of spike (S) glycoprotein, which plays an essential role in coronavirus infection, pathogenicity, transmission, and evolution. In this review, we brought together many studies narrating a sequence of events and highlighting the differences among S proteins from SARS-CoV, MERS-CoV, and SARS-CoV-2. It was performed here, analysis of S protein sequences and structures from the three pandemic coronaviruses pointing out the mutations among them and what they come through. Additionally, we investigated the receptor-binding domain (RBD) from all S proteins explaining the mutation and biological importance of all of them. Finally, we discuss the mutation in the S protein from several new isolates of SARS-CoV-2, reporting their difference and importance. This review brings into detail how the variations in S protein that make SARS-CoV-2 more aggressive than its relatives coronaviruses and other differences between coronaviruses.

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.

SARS-CoV-2 biology and variants: anticipation of viral evolution and what needs to be done

The global propagation of SARS-CoV-2 and the detection of a large number of variants, some of which have replaced the original clade to become dominant, underscores the fact that the virus is actively exploring its evolutionary space. The longer high levels of viral multiplication occur - permitted by high levels of transmission -, the more the virus can adapt to the human host and find ways to success. The third wave of the COVID-19 pandemic is starting in different parts of the world, emphasizing that transmission containment measures that are being imposed are not adequate. Part of the consideration in determining containment measures is the rationale that vaccination will soon stop transmission and allow a return to normality. However, vaccines themselves represent a selection pressure for evolution of vaccine-resistant variants, so the coupling of a policy of permitting high levels of transmission/virus multiplication during vaccine roll-out with the expectation that vaccines will deal with the pandemic, is unrealistic. In the absence of effective antivirals, it is not improbable that SARS-CoV-2 infection prophylaxis will involve an annual vaccination campaign against 'dominant' viral variants, similar to influenza prophylaxis. Living with COVID-19 will be an issue of SARS-CoV-2 variants and evolution. It is therefore crucial to understand how SARS-CoV-2 evolves and what constrains its evolution, in order to anticipate the variants that will emerge. Thus far, the focus has been on the receptor-binding spike protein, but the virus is complex, encoding 26 proteins which interact with a large number of host factors, so the possibilities for evolution are manifold and not predictable a priori. However, if we are to mount the best defence against COVID-19, we must mount it against the variants, and to do this, we must have knowledge about the evolutionary possibilities of the virus. In addition to the generic cellular interactions of the virus, there are extensive polymorphisms in humans (e.g. Lewis, HLA, etc.), some distributed within most or all populations, some restricted to specific ethnic populations and these variations pose additional opportunities for/constraints on viral evolution. We now have the wherewithal - viral genome sequencing, protein structure determination/modelling, protein interaction analysis - to functionally characterize viral variants, but access to comprehensive genome data is extremely uneven. Yet, to develop an understanding of the impacts of such evolution on transmission and disease, we must link it to transmission (viral epidemiology) and disease data (patient clinical data), and the population granularities of these. In this editorial, we explore key facets of viral biology and the influence of relevant aspects of human polymorphisms, human behaviour, geography and climate and, based on this, derive a series of recommendations to monitor viral evolution and predict the types of variants that are likely to arise.

Repurposing of Anticancer Drugs Expands Possibilities for Antiviral and Anti-Inflammatory Discovery in COVID-19

In 2020, the COVID-19 pandemic led to an unprecedented destabilization of the world's health and economic systems. The rapid spread and life-threatening consequences of COVID-19 have imposed testing of repurposed drugs, by investigating interventions already used in other indications, including anticancer drugs. The contours of anticancer drug repurposing have been shaped by similarities between the pathogenesis of COVID-19 and malignancies, including abnormal inflammatory and immunologic responses. In this review, we discuss the salient positive and negative points of repurposing anticancer drugs to advance treatments for COVID-19. SIGNIFICANCE: Targeting anti-inflammatory pathways with JAK/STAT inhibitors or anticytokine therapies aiming to curb COVID-19-related cytokine storm, using antiangiogenic drugs to reduce vascular abnormalities or immune-checkpoint inhibitors to improve antiviral defenses, could be of value in COVID-19. However, conflicting data on drug efficacy point to the need for better patient selection and biomarker studies.

The SARS-CoV-2 RNA-protein interactome in infected human cells

Characterizing the interactions that SARS-CoV-2 viral RNAs make with host cell proteins during infection can improve our understanding of viral RNA functions and the host innate immune response. Using RNA antisense purification and mass spectrometry, we identified up to 104 human proteins that directly and specifically bind to SARS-CoV-2 RNAs in infected human cells. We integrated the SARS-CoV-2 RNA interactome with changes in proteome abundance induced by viral infection and linked interactome proteins to cellular pathways relevant to SARS-CoV-2 infections. We demonstrated by genetic perturbation that cellular nucleic acid-binding protein (CNBP) and La-related protein 1 (LARP1), two of the most strongly enriched viral RNA binders, restrict SARS-CoV-2 replication in infected cells and provide a global map of their direct RNA contact sites. Pharmacological inhibition of three other RNA interactome members, PPIA, ATP1A1, and the ARP2/3 complex, reduced viral replication in two human cell lines. The identification of host dependency factors and defence strategies as presented in this work will improve the design of targeted therapeutics against SARS-CoV-2.

Plitidepsin has potent preclinical efficacy against SARS-CoV-2 by targeting the host protein eEF1A

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral proteins interact with the eukaryotic translation machinery, and inhibitors of translation have potent antiviral effects. We found that the drug plitidepsin (aplidin), which has limited clinical approval, possesses antiviral activity (90% inhibitory concentration = 0.88 nM) that is more potent than remdesivir against SARS-CoV-2 in vitro by a factor of 27.5, with limited toxicity in cell culture. Through the use of a drug-resistant mutant, we show that the antiviral activity of plitidepsin against SARS-CoV-2 is mediated through inhibition of the known target eEF1A (eukaryotic translation elongation factor 1A). We demonstrate the in vivo efficacy of plitidepsin treatment in two mouse models of SARS-CoV-2 infection with a reduction of viral replication in the lungs by two orders of magnitude using prophylactic treatment. Our results indicate that plitidepsin is a promising therapeutic candidate for COVID-19.

Comparative Genomics and Integrated Network Approach Unveiled Undirected Phylogeny Patterns, Co-mutational Hot Spots, Functional Cross Talk, and Regulatory Interactions in SARS-CoV-2

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has resulted in 92 million cases in a span of 1 year. The study focuses on understanding population-specific variations attributing its high rate of infections in specific geographical regions particularly in the United States. Rigorous phylogenomic network analysis of complete SARS-CoV-2 genomes (245) inferred five central clades named a (ancestral), b, c, d, and e (subtypes e1 and e2). Clade d and subclade e2 were found exclusively comprised of U.S. strains. Clades were distinguished by 10 co-mutational combinations in Nsp3, ORF8, Nsp13, S, Nsp12, Nsp2, and Nsp6. Our analysis revealed that only 67.46% of single nucleotide polymorphism (SNP) mutations were at the amino acid level. T1103P mutation in Nsp3 was predicted to increase protein stability in 238 strains except for 6 strains which were marked as ancestral type, whereas co-mutation (P409L and Y446C) in Nsp13 were found in 64 genomes from the United States highlighting its 100% co-occurrence. Docking highlighted mutation (D614G) caused reduction in binding of spike proteins with angiotensin-converting enzyme 2 (ACE2), but it also showed better interaction with the TMPRSS2 receptor contributing to high transmissibility among U.S. strains. We also found host proteins, MYO5A, MYO5B, and MYO5C, that had maximum interaction with viral proteins (nucleocapsid [N], spike [S], and membrane [M] proteins). Thus, blocking the internalization pathway by inhibiting MYO5 proteins which could be an effective target for coronavirus disease 2019 (COVID-19) treatment. The functional annotations of the host-pathogen interaction (HPI) network were found to be closely associated with hypoxia and thrombotic conditions, confirming the vulnerability and severity of infection. We also screened CpG islands in Nsp1 and N conferring the ability of SARS-CoV-2 to enter and trigger zinc antiviral protein (ZAP) activity inside the host cell.

IMPORTANCE In the current study, we presented a global view of mutational pattern observed in SARS-CoV-2 virus transmission. This provided a who-infect-whom geographical model since the early pandemic. This is hitherto the most comprehensive comparative genomics analysis of full-length genomes for co-mutations at different geographical regions especially in U.S. strains. Compositional structural biology results suggested that mutations have a balance of opposing forces affecting pathogenicity suggesting that only a few mutations are effective at the translation level. Novel HPI analysis and CpG predictions elucidate the proof of concept of hypoxia and thrombotic conditions in several patients. Thus, the current study focuses the understanding of population-specific variations attributing a high rate of SARS-CoV-2 infections in specific geographical regions which may eventually be vital for the most severely affected countries and regions for sharp development of custom-made vindication strategies.

Point of Care Diagnostic Devices for Rapid Detection of Novel Coronavirus (SARS-nCoV19) Pandemic: A Review

Coronaviruses are recognized as causative agents of human diseases worldwide. In Wuhan, China, an outbreak of Severe acute respiratory syndrome novel Coronavirus (SARS-nCoV-2) was reported at the end of December 2019, causing 63 million COVID cases and 1.3 million deaths globally by 2 December, 2020. The transmission risk forecasts and the SARS-nCoV-2 epidemic pattern are progressive. Unfortunately, there is no specific FDA approved drugs or vaccines available currently to treat SARS-nCoV-2. In response to nCoV-2 spread, the rapid detection is crucial for estimating the severity of the disease and treatment of patients. Currently, there are several RT-PCR based diagnostic kits available for SARS-nCoV-2 detection, which are time-consuming, expensive, need advanced equipment facilities and trained personnel. The cost of diagnosis and the unavailability of sufficient test kits may prevent to check community transmission. Furthermore, expanding the testing facilities in asymptomatic cases in hotspots require more Point of Care (PoC) devices. Therefore, fast, inexpensive, and reliable methods of detection of SARS-nCoV-2 virus infection in humans is urgently required. The rapid and easy-to-use devices will facilitate onsite testing. In this review, nucleic acid assays, serological assays, multiplex assays, and PoC devices are discussed to understand various diagnostic approaches to reduce the spread and mortality rate in the future. Aptamer based detection is most specific, inexpensive and rapid detection of SARS-nCoV-2 without laboratory tools. To the best of our knowledge more than 900 SARS-nCoV-2 test kits are in pipeline, among 395 test kits are molecular bested test kits and only few test kits are developed using Aptamer technology https://www.finddx.org/covid-19/pipeline/.

Nucleic Acid-Sensing Pathways During SARS-CoV-2 Infection: Expectations versus Reality

The coronavirus disease 2019 (COVID-19) pandemic has affected millions of people and crippled economies worldwide. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for this pandemic has triggered avid research on its pathobiology to better understand the pathophysiology of COVID-19. In the absence of approved antiviral therapeutic strategies or vaccine platforms capable of effectively targeting this global threat, the hunt for effective therapeutics has led to many candidates being actively evaluated for their efficacy in controlling or preventing COVID-19. In this review, we gathered current evidence on the innate nucleic acid-sensing pathways expected to be elicited by SARS-CoV-2 and the immune evasion mechanisms they have developed to promote viral replication and infection. Within the nucleic acid-sensing pathways, SARS-CoV-2 infection and evasion mechanisms trigger the activation of NOD-signaling and NLRP3 pathways leading to the production of inflammatory cytokines, IL-1β and IL-6, while muting or blocking cGAS-STING and interferon type I and III pathways, resulting in decreased production of antiviral interferons and delayed innate response. Therefore, blocking the inflammatory arm and boosting the interferon production arm of nucleic acid-sensing pathways could facilitate early control of viral replication and dissemination, prevent disease progression, and cytokine storm development. We also discuss the rationale behind therapeutic modalities targeting these sensing pathways and their implications in the treatment of COVID-19.

Cyclophilin A: a key player for etiological agent infection

Abstract

Cyclophilin A (CypA), a key member of the immunophilin family, is the most abundantly expressed isozyme of the 18 known human cyclophilins. Besides acting as an intracellular receptor for cyclosporine A, CypA plays a vital role in microorganismal infections, cardiovascular diseases, liver diseases, kidney diseases, neurodegeneration, cancer, rheumatoid arthritis, periodontitis, sepsis, asthma, and aging. This review focuses on the pivotal roles of CypA in the infection of etiological agents, which manifests mainly in promoting or inhibiting viral replication based on the host cell type and viral species. CypA can interact with viral proteins and thus regulate the replication cycle of the virus. CypA is involved in pathogenic bacterial infections by regulating the formation of host actin skeleton or membrane translocation of bacterial toxins, or mediated the adhesion of Mycoplasma genitalium during the infection processes by acting as a cellular receptor of M. genitalium. CypA also plays a critical role in infection or the life cycle of certain parasites or host immune regulation. Moreover, we summarized the current understanding of CypA inhibitors acting as host-targeting antiviral agents, thus opening an avenue for the treatment of multiple viral infections due to their broad antiviral effects and ability to effectively prevent drug resistance. Therefore, the antiviral effect of CypA has the potential to promote CypA inhibitors as host-targeting drugs to CypA-involved etiological agent infections and human diseases.

Key points

• CypA is involved in the replication and infection of several viruses, pathogenic bacteria, mycoplasma, and parasites.

• CypA inhibitors are in a strong position to inhibit the infection of viruses, bacterial, and mycoplasma.

Spatial and temporal roles of SARS-CoV PLpro -A snapshot

SARS‐CoV and SARS‐CoV‐2 encode four structural and accessory proteins (spike, envelope, membrane and nucleocapsid proteins) and two polyproteins (pp1a and pp1ab). The polyproteins are further cleaved by 3C‐like cysteine protease (3CL^pro) and papain‐like protease (PL^pro) into 16 nonstructural proteins (nsps). PL^pro is released from nsp3 through autocleavage, and then it cleaves the sites between nsp1/2, between nsp2/3 and between nsp3/4 with recognition motif of LXGG, and the sites in the C‐terminus of ubiquitin and of protein interferon‐stimulated gene 15 (ISG15) with recognition motif of RLRGG. Alone or together with SARS unique domain (SUD), PL^pro can stabilize an E3 ubiquitin ligase, the ring‐finger, and CHY zinc‐finger domain‐containing 1 (RCHY1), through domain interaction, and thus, promote RCHY1 to ubiquitinate its target proteins including p53. However, a dilemma appears in terms of PL^pro roles. On the one hand, the ubiquitination of p53 is good for SARS‐CoV because the ubiquitinated p53 cannot inhibit SARS‐CoV replication. On the other hand, the ubiquitination of NF‐κB inhibitor (IκBα), TNF receptor‐associated factors (TRAFs), and stimulator of interferon gene (STING), and the ISGylation of targeted proteins are bad for SARS‐CoV because these ubiquitination and ISGylation initiate the innate immune response and antiviral state. This mini‐review analyzes the dilemma and provides a snapshot on how the viral PL^pro smartly manages its roles to avoid its simultaneously contradictory actions, which could shed lights on possible strategies to deal with SARS‐CoV‐2 infections.

Inhibiting the reproduction of SARS-CoV-2 through perturbations in human lung cell metabolic network

Viruses rely on their host for reproduction. Here, we made use of genomic and structural information to create a biomass function capturing the amino and nucleic acid requirements of SARS-CoV-2. Incorporating this biomass function into a stoichiometric metabolic model of the human lung cell and applying metabolic flux balance analysis, we identified host-based metabolic perturbations inhibiting SARS-CoV-2 reproduction. Our results highlight reactions in the central metabolism, as well as amino acid and nucleotide biosynthesis pathways. By incorporating host cellular maintenance into the model based on available protein expression data from human lung cells, we find that only few of these metabolic perturbations are able to selectively inhibit virus reproduction. Some of the catalysing enzymes of such reactions have demonstrated interactions with existing drugs, which can be used for experimental testing of the presented predictions using gene knockouts and RNA interference techniques. In summary, the developed computational approach offers a platform for rapid, experimentally testable generation of drug predictions against existing and emerging viruses based on their biomass requirements.

SARS-CoV-2 infection: a global outbreak and its implication on public health

BACKGROUND

A novel corona virus is formally named as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which results in causing coronavirus disease 2019 (COVID-19). It is the latest prevalent pandemic worldwide when compared to other infectious diseases like Avian flu, Middle East respiratory syndrome and severe acute respiratory syndrome (SARS).

MAIN BODY

Coronavirus disease 2019 (COVID-19) is currently occurring pandemic over world. It was emerged in Wuhan, China, in the end of December 2019 and spreading across worldwide. As the coronavirus is spreading easily through direct contact with infected people droplets, inhalation, and also air droplets, it hit up a huge amount of population even reported with death. Still, with small amounts of asymptomatic transmission between people it spreads throughout the globe. People need special care to protect from the transmission of disease. However, there are no drugs so far that shows efficacy; there is an immediate need for the development of vaccines. In order to decrease the COVID-19 cases, organizations rapidly involve in the preparation of vaccine and many vaccines have been developed by various countries. The governments took safety measures to control the spread of virus and also to minimize morbidity and mortality rate to least possible.

CONCLUSION

The purpose of this review article is to increase our understanding of COVID-19 and facilitate the people to take a move in facing challenges of the world.

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.

Structural Characterization of SARS-CoV-2: Where We Are, and Where We Need to Be

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly spread in humans in almost every country, causing the disease COVID-19. Since the start of the COVID-19 pandemic, research efforts have been strongly directed towards obtaining a full understanding of the biology of the viral infection, in order to develop a vaccine and therapeutic approaches. In particular, structural studies have allowed to comprehend the molecular basis underlying the role of many of the SARS-CoV-2 proteins, and to make rapid progress towards treatment and preventive therapeutics. Despite the great advances that have been provided by these studies, many knowledge gaps on the biology and molecular basis of SARS-CoV-2 infection still remain. Filling these gaps will be the key to tackle this pandemic, through development of effective treatments and specific vaccination strategies.