Coronavirus NSP6 restricts autophagosome expansion

Spectrum of COVID-19 induced liver injury: A review report

The coronavirus disease 2019 (COVID-19) pandemic has caused changes in the global health system, causing significant setbacks in healthcare systems worldwide. This pandemic has also shown resilience, flexibility, and creativity in reacting to the tragedy. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection targets most of the respiratory tract, resulting in a severe sickness called acute respiratory distress syndrome that may be fatal in some individuals. Although the lung is the primary organ targeted by COVID-19 viruses, the clinical aspect of the disease is varied and ranges from asymptomatic to respiratory failure. However, due to an unorganized immune response and several affected mechanisms, the liver may also experience liver cell injury, ischemic liver dysfunction, and drug-induced liver injury, which can result in respiratory failure because of the immune system's disordered response and other compromised processes that can end in multisystem organ failure. Patients with liver cirrhosis or those who have impaired immune systems may be more likely than other groups to experience worse results from the SARS-CoV-2 infection. We thus intend to examine the pathogenesis, current therapy, and consequences of liver damage concerning COVID-19.

PIP4K2C inhibition reverses autophagic flux impairment induced by SARS-CoV-2

In search for broad-spectrum antivirals, we discovered a small molecule inhibitor, RMC-113, that potently suppresses the replication of multiple RNA viruses including SARS-CoV-2 in human lung organoids. We demonstrated selective dual inhibition of the lipid kinases PIP4K2C and PIKfyve by RMC-113 and target engagement by its clickable analog. Advanced lipidomics revealed alteration of SARS-CoV-2-induced phosphoinositide signature by RMC-113 and linked its antiviral effect with functional PIP4K2C and PIKfyve inhibition. We discovered PIP4K2C's roles in SARS-CoV-2 entry, RNA replication, and assembly/egress, validating it as a druggable antiviral target. Integrating proteomics, single-cell transcriptomics, and functional assays revealed that PIP4K2C binds SARS-CoV-2 nonstructural protein 6 and regulates virus-induced impairment of autophagic flux. Reversing this autophagic flux impairment is a mechanism of antiviral action of RMC-113. These findings reveal virus-induced autophagy regulation via PIP4K2C, an understudied kinase, and propose dual inhibition of PIP4K2C and PIKfyve as a candidate strategy to combat emerging viruses.

Differential beta-coronavirus infection dynamics in human bronchial epithelial organoids

The lower respiratory system serves as the target and barrier for beta-coronavirus (beta-CoV) infections. In this study, we explored beta-CoV infection dynamics in human bronchial epithelial (HBE) organoids, focusing on HCoV-OC43, SARS-CoV, MERS-CoV, and SARS-CoV-2. Utilizing advanced organoid culture techniques, we observed robust replication for all beta-CoVs, particularly noting that SARS-CoV-2 reached peak viral RNA levels at 72 h postinfection. Through comprehensive transcriptomic analysis, we identified significant shifts in cell population dynamics, marked by an increase in goblet cells and a concurrent decrease in ciliated cells. Furthermore, our cell tropism analysis unveiled distinct preferences in viral targeting: HCoV-OC43 predominantly infected club cells, while SARS-CoV had a dual tropism for goblet and ciliated cells. In contrast, SARS-CoV-2 primarily infected ciliated cells, and MERS-CoV showed a marked affinity for goblet cells. Host factor analysis revealed the upregulation of genes encoding viral receptors and proteases. Notably, HCoV-OC43 induced the unfolded protein response pathway, which may facilitate viral replication. Our study also reveals a complex interplay between inflammatory pathways and the suppression of interferon responses during beta-CoV infections. These findings provide insights into host-virus interactions and antiviral defense mechanisms, contributing to our understanding of beta-CoV infections in the respiratory tract.

Differences and similarities between innate immune evasion strategies of human coronaviruses

So far, seven coronaviruses have emerged in humans. Four recurring endemic coronaviruses cause mild respiratory symptoms. Infections with epidemic Middle East respiratory syndrome-related coronavirus or severe acute respiratory syndrome coronavirus (SARS-CoV)-1 are associated with high mortality rates. SARS-CoV-2 is the causative agent of the coronavirus disease 2019 pandemic. To establish an infection, coronaviruses evade restriction by human innate immune defenses, such as the interferon system, autophagy and the inflammasome. Here, we review similar and distinct innate immune manipulation strategies employed by the seven human coronaviruses. We further discuss the impact on pathogenesis, zoonotic emergence and adaptation. Understanding the nature of the interplay between endemic/epidemic/pandemic coronaviruses and host defenses may help to better assess the pandemic potential of emerging coronaviruses.

NSP6 inhibits the production of ACE2-containing exosomes to promote SARS-CoV-2 infectivity

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has triggered a global pandemic, which severely endangers public health. Our and others' works have shown that the angiotensin-converting enzyme 2 (ACE2)-containing exosomes (ACE2-exos) have superior antiviral efficacies, especially in response to emerging variants. However, the mechanisms of how the virus counteracts the host and regulates ACE2-exos remain unclear. Here, we identified that SARS-CoV-2 nonstructural protein 6 (NSP6) inhibits the production of ACE2-exos by affecting the protein level of ACE2 as well as tetraspanin-CD63 which is a key factor for exosome biogenesis. We further found that the protein stability of CD63 and ACE2 is maintained by the deubiquitination of proteasome 26S subunit, non-ATPase 12 (PSMD12). NSP6 interacts with PSMD12 and counteracts its function, consequently promoting the degradation of CD63 and ACE2. As a result, NSP6 diminishes the antiviral efficacy of ACE2-exos and facilitates the virus to infect healthy bystander cells. Overall, our study provides a valuable target for the discovery of promising drugs for the treatment of coronavirus disease 2019.

IMPORTANCE

The outbreak of coronavirus disease 2019 (COVID-19) severely endangers global public health. The efficacy of vaccines and antibodies declined with the rapid emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mutants. Angiotensin-converting enzyme 2-containing exosomes (ACE2-exos) therapy exhibits a broad neutralizing activity, which could be used against various viral mutations. Our study here revealed that SARS-CoV-2 nonstructural protein 6 inhibited the production of ACE2-exos, thereby promoting viral infection to the adjacent bystander cells. The identification of a new target for blocking SARS-CoV-2 depends on fully understanding the virus-host interaction networks. Our study sheds light on the mechanism by which the virus resists the host exosome defenses, which would facilitate the study and design of ACE2-exos-based therapeutics for COVID-19.

The relationship between autophagy and respiratory viruses

Respiratory viruses have caused severe global health problems and posed essential challenges to the medical community. In recent years, the role of autophagy as a critical process in cells in viral respiratory diseases has been noticed. One of the vital catabolic biological processes in the body is autophagy. Autophagy contributes to energy recovery by targeting and selectively directing foreign microorganisms, organelles, and senescent intracellular proteins to the lysosome for degradation and phagocytosis. Activation or suppression of autophagy is often initiated when foreign pathogenic organisms such as viruses infect cells. Because of its antiviral properties, several viruses may escape or resist this process by encoding viral proteins. Viruses can also use autophagy to enhance their replication or prolong the persistence of latent infections. Here, we provide an overview of autophagy and respiratory viruses such as coronavirus, rhinovirus, parainfluenza, influenza, adenovirus, and respiratory syncytial virus, and examine the interactions between them and the role of autophagy in the virus-host interaction process and the resulting virus replication strategy.

Multiple Lines of Evidence Support 199 SARS-CoV-2 Positively Selected Amino Acid Sites

SARS-CoV-2 amino acid variants that contribute to an increased transmissibility or to host immune system escape are likely to increase in frequency due to positive selection and may be identified using different methods, such as codeML, FEL, FUBAR, and MEME. Nevertheless, when using different methods, the results do not always agree. The sampling scheme used in different studies may partially explain the differences that are found, but there is also the possibility that some of the identified positively selected amino acid sites are false positives. This is especially important in the context of very large-scale projects where hundreds of analyses have been performed for the same protein-coding gene. To account for these issues, in this work, we have identified positively selected amino acid sites in SARS-CoV-2 and 15 other coronavirus species, using both codeML and FUBAR, and compared the location of such sites in the different species. Moreover, we also compared our results to those that are available in the COV2Var database and the frequency of the 10 most frequent variants and predicted protein location to identify those sites that are supported by multiple lines of evidence. Amino acid changes observed at these sites should always be of concern. The information reported for SARS-CoV-2 can also be used to identify variants of concern in other coronaviruses.

Inhibition of porcine deltacoronavirus entry and replication by Cepharanthine

Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus (CoV) that mainly causes acute diarrhea/vomiting, dehydration, and mortality in piglets, possessing economic losses and public health concerns. However, there are currently no proven effective antiviral agents against PDCoV. Cepharanthine (CEP) is a naturally occurring alkaloid used as a traditional remedy for radiation-induced symptoms, but its underlying mechanism of CEP against PDCoV has remained elusive. The aim of this study was to investigate the anti-PDCoV effects and mechanisms of CEP in LLC-PK1 cells. The results showed that the antiviral activity of CEP was based on direct action on cells, preventing the virus from attaching to host cells and virus replication. Importantly, Surface Plasmon Resonance (SPR) results showed that CEP has a moderate affinity to PDCoV receptor, porcine aminopeptidase N (pAPN) protein. AutoDock predicted that CEP can form hydrogen bonds with amino acid residues (R740, N783, and R790) in the binding regions of PDCoV and pAPN. In addition, RT-PCR results showed that CEP treatment could significantly reduce the transcription of ZBP1, cytokine (IL-1β and IFN-α) and chemokine genes (CCL-2, CCL-4, CCL-5, CXCL-2, CXCL-8, and CXCL-10) induced by PDCoV. Western blot analysis revealed that CEP could inhibit viral replication by inducing autophagy. In conclusion, our results suggest that the anti-PDCoV activity of CEP is not only relies on competing the virus binding with pAPN, but also affects the proliferation of the virus in vitro by downregulating the excessive immune response caused by the virus and inducing autophagy. CEP emerges as a promising candidate for potential anti-PDCoV therapeutic development.

Amino acid substitution L232F in non-structural protein 6 identified as a possible human-adaptive mutation in clade B MERS coronaviruses

IMPORTANCE

Viral host adaptation plays an important role in inter-species transmission of coronaviruses and influenza viruses. Multiple human-adaptive mutations have been identified in influenza viruses but not so far in MERS-CoV that circulates widely in dromedary camels in the Arabian Peninsula leading to zoonotic transmission. Here, we analyzed clade B MERS-CoV sequences and identified an amino acid substitution L232F in nsp6 that repeatedly occurs in human MERS-CoV. Using a loss-of-function reverse genetics approach, we found the nsp6 L232F conferred increased viral replication competence in vitro, in cultures of the upper human respiratory tract ex vivo, and in lungs of mice infected in vivo. Our results showed that nsp6 L232F may be an adaptive mutation associated with zoonotic transmission of MERS-CoV. This study highlighted the capacity of MERS-CoV to adapt to transmission to humans and also the need for continued surveillance of MERS-CoV in camels.

A review of SARS-CoV-2 variants and vaccines: Viral properties, mutations, vaccine efficacy, and safety

The severe acute respiratory syndrome coronavirus disease 2 instigated by coronavirus disease of 2019 (COVID-19) has delivered an unfathomable obstruction that has touched all sectors worldwide. Despite new vaccine technologies and mass administration of booster doses, the virus persists, and unknown the ending of the pandemic for new variants and sub-variants. Moreover, whether leaning on home medications or using plant extracts is sufficient often to combat the virus has generated tremendous interest in the scientific fraternity. Different databases including PubMed, Scopus, Web of Science, and Google Scholar used to find published articles linked with related topics. Currently, COVID-19 third and fourth shots of vaccines are progressively administered worldwide, where some countries trail others by a significant margin. Many proteins related to viral activity have changed, possibly boosting the virus infectivity and making antibodies ineffective. This study will reminisce the viral genome, associated pathways for viral protein functions, variants, and their mutations. The current, comprehensive review will also provide information on vaccine technologies developed by several biotech companies and the efficacy of their doses, costs including boosters on a mass level. As no vaccine is working to protect fully against all the variants, the new proactive vaccine research needs to be conducted based on all variants, their sub-lineage, and mutations.

SARS-CoV-2 nonstructural protein 6 triggers endoplasmic reticulum stress-induced autophagy to degrade STING1

ABBREVIATIONS

aa: amino acid; ATF6: activating transcription factor 6; ATG5: autophagy related 5; CCPG1: cell cycle progression 1; CFTR: CF transmembrane conductance regulator; cGAMP: cyclic GMP-AMP; CGAS: cyclic GMP-AMP synthase; CHX: cycloheximide; Co-IP: co-immunoprecipitation; CQ: chloroquine; EIF2A/eIF2α: eukaryotic translation initiation factor 2A; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; ERN1/IRE1: endoplasmic reticulum to nucleus signaling 1; GFP: green fluorescent protein; HSPA5/GRP78: heat shock protein family A (Hsp70) member 5; HSV-1: herpes simplex virus type 1; IFIT1: interferon induced protein with tetratricopeptide repeats 1; IFNB1/IFN-β: interferon beta 1; IRF3: interferon regulatory factor 3; ISG15: ISG15 ubiquitin like modifier; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAP3K7/TAK1: mitogen-activated protein kinase kinase kinase 7; MAVS: mitochondrial antiviral signaling protein; MOI: multiplicity of infection; NFKB/NF-κB: nuclear factor kappa B; NSP6: non-structural protein 6; Δ106-108: deletion of amino acids 106-108 in NSP6 of SARS-CoV-2; Δ105-107: deletion of amino acids 105-107 in NSP6 of SARS-CoV-2; RETREG1/FAM134B: reticulophagy regulator 1; RIGI/DDX58: RNA sensor RIG-I; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TBK1: TANK binding kinase 1.

Lipid compartments and lipid metabolism as therapeutic targets against coronavirus

Lipids perform a series of cellular functions, establishing cell and organelles' boundaries, organizing signaling platforms, and creating compartments where specific reactions occur. Moreover, lipids store energy and act as secondary messengers whose distribution is tightly regulated. Disruption of lipid metabolism is associated with many diseases, including those caused by viruses. In this scenario, lipids can favor virus replication and are not solely used as pathogens' energy source. In contrast, cells can counteract viruses using lipids as weapons. In this review, we discuss the available data on how coronaviruses profit from cellular lipid compartments and why targeting lipid metabolism may be a powerful strategy to fight these cellular parasites. We also provide a formidable collection of data on the pharmacological approaches targeting lipid metabolism to impair and treat coronavirus infection.

Resolving a guanine-quadruplex structure in the SARS-CoV-2 genome through circular dichroism and multiscale molecular modeling

The genome of SARS-CoV-2 coronavirus is made up of a single-stranded RNA fragment that can assume a specific secondary structure, whose stability can influence the virus's ability to reproduce. Recent studies have identified putative guanine quadruplex sequences in SARS-CoV-2 genome fragments that are involved in coding for both structural and non-structural proteins. In this contribution, we focus on a specific G-rich sequence referred to as RG-2, which codes for the non-structural protein 10 (Nsp10) and assumes a guanine-quadruplex (G4) arrangement. We provide the secondary structure of RG-2 G4 at atomistic resolution by molecular modeling and simulation, validated by the superposition of experimental and calculated electronic circular dichroism spectra. Through both experimental and simulation approaches, we have demonstrated that pyridostatin (PDS), a widely recognized G4 binder, can bind to and stabilize RG-2 G4 more strongly than RG-1, another G4 forming sequence that was previously proposed as a potential target for antiviral drug candidates. Overall, this study highlights RG-2 as a valuable target to inhibit the translation and replication of SARS-CoV-2, paving the way towards original therapeutic approaches against emerging RNA viruses.

Targeting SARS-CoV-2 Non-Structural Proteins

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an enveloped respiratory β coronavirus that causes coronavirus disease (COVID-19), leading to a deadly pandemic that has claimed millions of lives worldwide. Like other coronaviruses, the SARS-CoV-2 genome also codes for non-structural proteins (NSPs). These NSPs are found within open reading frame 1a (ORF1a) and open reading frame 1ab (ORF1ab) of the SARS-CoV-2 genome and encode NSP1 to NSP11 and NSP12 to NSP16, respectively. This study aimed to collect the available literature regarding NSP inhibitors. In addition, we searched the natural product database looking for similar structures. The results showed that similar structures could be tested as potential inhibitors of the NSPs.

Mechanism of the Covalent Inhibition of Human Transmembrane Protease Serine 2 as an Original Antiviral Strategy

The Transmembrane Protease Serine 2 (TMPRSS2) is a human enzyme which is involved in the maturation and post-translation of different proteins. In addition to being overexpressed in cancer cells, TMPRSS2 plays a further fundamental role in favoring viral infections by allowing the fusion of the virus envelope with the cellular membrane, notably in SARS-CoV-2. In this contribution, we resort to multiscale molecular modeling to unravel the structural and dynamical features of TMPRSS2 and its interaction with a model lipid bilayer. Furthermore, we shed light on the mechanism of action of a potential inhibitor (nafamostat), determining the free-energy profile associated with the inhibition reaction and showing the facile poisoning of the enzyme. Our study, while providing the first atomistically resolved mechanism of TMPRSS2 inhibition, is also fundamental in furnishing a solid framework for further rational design targeting transmembrane proteases in a host-directed antiviral strategy.

The interplay between lipid droplets and virus infection

As an intracellular parasite, the virus usurps cellular machinery and modulates cellular metabolism pathways to replicate itself in cells. Lipid droplets (LDs) are universally conserved energy storage organelles that not only play vital roles in maintaining lipid homeostasis but are also involved in viral replication. Increasing evidence has demonstrated that viruses take advantage of cellular lipid metabolism by targeting the biogenesis, hydrolysis, and lipophagy of LD during viral infection. In this review, we summarize the current knowledge about the modulation of cellular LD by different viruses, with a special emphasis on the Hepatitis C virus, Dengue virus, and SARS-CoV-2.

Role and clinical implication of autophagy in COVID-19

The ongoing coronavirus disease 2019 (COVID-19) pandemic constitutes a serious public health concern worldwide. Currently, more than 6 million deaths have occurred despite drastic containment measures, and this number is still increasing. Currently, no standard therapies for COVID-19 are available, which necessitates identifying effective preventive and therapeutic agents against COVID-19. However, developing new drugs and vaccines is a time-consuming process, and therefore, repurposing the existing drugs or redeveloping related targets seems to be the best strategy to develop effective therapeutics against COVID-19. Autophagy, a multistep lysosomal degradation pathway contributing to nutrient recycling and metabolic adaptation, is involved in the initiation and progression of numerous diseases as a part of an immune response. The key role of autophagy in antiviral immunity has been extensively studied. Moreover, autophagy can directly eliminate intracellular microorganisms by selective autophagy, that is, "xenophagy." However, viruses have acquired diverse strategies to exploit autophagy for their infection and replication. This review aims to trigger the interest in the field of autophagy as an antiviral target for viral pathogens (with an emphasis on COVID-19). We base this hypothesis on summarizing the classification and structure of coronaviruses as well as the process of SARS-CoV-2 infection and replication; providing the common understanding of autophagy; reviewing interactions between the mechanisms of viral entry/replication and the autophagy pathways; and discussing the current state of clinical trials of autophagy-modifying drugs in the treatment of SARS-CoV-2 infection. We anticipate that this review will contribute to the rapid development of therapeutics and vaccines against COVID-19.

The multiple roles of nsp6 in the molecular pathogenesis of SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to evolve and adapt after its emergence in late 2019. As the causative agent of the coronavirus disease 2019 (COVID-19), the replication and pathogenesis of SARS-CoV-2 have been extensively studied by the research community for vaccine and therapeutics development. Given the importance of viral spike protein in viral infection/transmission and vaccine development, the scientific community has thus far primarily focused on studying the structure, function, and evolution of the spike protein. Other viral proteins are understudied. To fill in this knowledge gap, a few recent studies have identified nonstructural protein 6 (nsp6) as a major contributor to SARS-CoV-2 replication through the formation of replication organelles, antagonism of interferon type I (IFN-I) responses, and NLRP3 inflammasome activation (a major factor of severe disease in COVID-19 patients). Here, we review the most recent progress on the multiple roles of nsp6 in modulating SARS-CoV-2 replication and pathogenesis.

Autophagy and SARS-CoV-2-Old Players in New Games

At present it is well-defined that autophagy is a fundamental process essential for cell life but its pro-viral and anti-viral role has been stated out with the COVID pandemic. However, viruses in turn have evolved diverse adaptive strategies to cope with autophagy driven host defense, either by blocking or hijacking the autophagy machinery for their own benefit. The mechanisms underlying autophagy modulation are presented in the current review which summarizes the accumulated knowledge on the crosstalk between autophagy and viral infections, with a particular emphasizes on SARS-CoV-2. The different types of autophagy related to infections and their molecular mechanisms are focused in the context of inflammation. In particular, SARS-CoV-2 entry, replication and disease pathogenesis are discussed. Models to study autophagy and to formulate novel treatment approaches and pharmacological modulation to fight COVID-19 are debated. The SARS-CoV-2-autophagy interplay is presented, revealing the complex dynamics and the molecular machinery of autophagy. The new molecular targets and strategies to treat COVID-19 effectively are envisaged. In conclusion, our finding underline the importance of development new treatment strategies and pharmacological modulation of autophagy to fight COVID-19.

How SARS-CoV-2 Alters the Regulation of Gene Expression in Infected Cells

Nonstructural accessory proteins in viruses play a key role in hijacking the basic cellular mechanisms, which is essential to promote the virus survival and evasion of the immune system. The immonuglobulin-like open reading frame 8 (ORF8) protein expressed by SARS-CoV-2 accumulates in the nucleus and may influence the regulation of the gene expression in infected cells. In this contribution, by using microsecond time-scale all-atom molecular dynamics simulations, we unravel the structural bases behind the epigenetic action of ORF8. In particular, we highlight how the protein is able to form stable aggregates with DNA through a histone tail-like motif, and how this interaction is influenced by post-translational modifications, such as acetylation and methylation, which are known epigenetic markers in histones. Our work not only clarifies the molecular mechanisms behind the perturbation of the epigenetic regulation caused by the viral infection but also offers an unusual perspective which may foster the development of original antivirals.

Subversion of autophagy machinery and organelle-specific autophagy by SARS-CoV-2 and coronaviruses

As a new emerging severe coronavirus, the knowledge on the SARS-CoV-2 and COVID-19 remains very limited, whereas many concepts can be learned from the homologous coronaviruses. Macroautophagy/autophagy is finely regulated by SARS-CoV-2 infection and plays important roles in SARS-CoV-2 infection and pathogenesis. This review will explore the subversion and mechanism of the autophagy-related machinery, vacuoles and organelle-specific autophagy during infection of SARS-CoV-2 and coronaviruses to provide meaningful insights into the autophagy-related therapeutic strategies for infectious diseases of SARS-CoV-2 and coronaviruses.

Mutation nsp6 L232F associated with MERS-CoV zoonotic transmission confers higher viral replication in human respiratory tract cultures ex-vivo

Middle East respiratory syndrome coronavirus (MERS-CoV) causes zoonotic disease. Dromedary camels are the source of zoonotic infection. We identified a mutation of amino acid leucine to phenylalanine in the codon 232 position of the non-structural protein 6 (nsp6) (nsp6 L232F) that is repeatedly associated with zoonotic transmission. We generated a pair of isogenic recombinant MERS-CoV with nsp6 232L and 232F residues, respectively, and showed that the nsp6 L232F mutation confers higher replication competence in ex-vivo culture of human nasal and bronchial tissues and in lungs of mice experimentally infected in-vivo. Mechanistically, the nsp6 L232F mutation appeared to modulate autophagy and was associated with higher exocytic virus egress, while innate immune responses and zippering activity of the endoplasmic reticulum remained unaffected. Our study suggests that MERS-CoV nsp6 may contribute to viral adaptation to humans. This highlights the importance of continued surveillance of MERS-CoV in both camels and humans.

Spike and nsp6 are key determinants of SARS-CoV-2 Omicron BA.1 attenuation

The SARS-CoV-2 Omicron variant is more immune evasive and less virulent than other major viral variants that have so far been recognized1-12. The Omicron spike (S) protein, which has an unusually large number of mutations, is considered to be the main driver of these phenotypes. Here we generated chimeric recombinant SARS-CoV-2 encoding the S gene of Omicron (BA.1 lineage) in the backbone of an ancestral SARS-CoV-2 isolate, and compared this virus with the naturally circulating Omicron variant. The Omicron S-bearing virus robustly escaped vaccine-induced humoral immunity, mainly owing to mutations in the receptor-binding motif; however, unlike naturally occurring Omicron, it efficiently replicated in cell lines and primary-like distal lung cells. Similarly, in K18-hACE2 mice, although virus bearing Omicron S caused less severe disease than the ancestral virus, its virulence was not attenuated to the level of Omicron. Further investigation showed that mutating non-structural protein 6 (nsp6) in addition to the S protein was sufficient to recapitulate the attenuated phenotype of Omicron. This indicates that although the vaccine escape of Omicron is driven by mutations in S, the pathogenicity of Omicron is determined by mutations both in and outside of the S protein.

Neutrophil autophagy and NETosis in COVID-19: perspectives

The COVID-19 pandemic has caused substantial losses worldwide in people's lives, health, and property. Currently, COVID-19 is still prominent worldwide without any specific drug treatment. The SARS-CoV-2 pathogen is the cause of various systemic diseases, mainly acute pneumonia. Within the pathological process, neutrophils are recruited to infected sites, especially in the lungs, for the first stage of removing invading SARS-CoV-2 through a range of mechanisms. Macroautophagy/autophagy, a conserved autodegradation process in neutrophils, plays a crucial role in the neutrophil phagocytosis of pathogens. NETosis refers to neutrophil cell death, while auto-inflammatory factors and antigens release NETs. This review summarizes the latest research progress and provides an in-depth explanation of the underlying mechanisms of autophagy and NETosis in COVID-19. Furthermore, after exploring the relationship between autophagy and NETosis, we discuss potential targets and treatment options. This review keeps up with the latest research on COVID-19 from neutrophil autophagy and NETosis with a new perspective, which can guide the urgent development of antiviral drugs and provide guidance for the clinical treatment of COVID-19.Abbreviations: AKT1: AKT serine/threonine kinase 1; AMPK: AMP-activated protein kinase; AP: autophagosome; ARDS: acute respiratory distress syndrome; ATG: autophagy related; BECN1: beclin 1; cfDNA: cell-free DNA; COVID-19: coronavirus disease 2019; CQ: chloroquine; DMVs: double-membrane vesicles; ELANE/NE: elastase, neutrophil expressed; F3: coagulation factor III, tissue factor; HCQ: hydroxychloroquine; MAP1LC3/LC3: microtubule associated protein 1 light chain of 3; MPO: myeloperoxidase; MTORC1: mechanistic target of rapamycin kinase complex 1; NETs: neutrophil traps; NSP: nonstructural protein; PI3K: class I phosphoinositide 3-kinase; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol-3-phosphate; ROS: reactive oxygen species; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; SKP2: S-phase kinase associated protein 2; TCC: terminal complement complex; ULK1: unc-51 like.

Targeting viral proteins for restraining SARS-CoV-2: focusing lens on viral proteins beyond spike for discovering new drug targets

INTRODUCTION

Emergence of highly infectious SARS-CoV-2 variants are reducing protection provided by current vaccines, requiring constant updates in antiviral approaches. The virus encodes four structural and sixteen nonstructural proteins which play important roles in viral genome replication and transcription, virion assembly, release , entry into cells, and compromising host cellular defenses. As alien proteins to host cells, many viral proteins represent potential targets for combating the SARS-CoV-2.

AREAS COVERED

Based on literature from PubMed and Web of Science databases, the authors summarize the typical characteristics of SARS-CoV-2 from the whole viral particle to the individual viral proteins and their corresponding functions in virus life cycle. The authors also discuss the potential and emerging targeted interventions to curb virus replication and spread in detail to provide unique insights into SARS-CoV-2 infection and countermeasures against it.

EXPERT OPINION

Our comprehensive analysis highlights the rationale to focus on non-spike viral proteins that are less mutated but have important functions. Examples of this include: structural proteins (e.g. nucleocapsid protein, envelope protein) and extensively-concerned nonstructural proteins (e.g. NSP3, NSP5, NSP12) along with the ones with relatively less attention (e.g. NSP1, NSP10, NSP14 and NSP16), for developing novel drugs to overcome resistance of SARS-CoV-2 variants to preexisting vaccines and antibody-based treatments.

Dantrolene and ryanodine receptors in COVID-19: The daunting task and neglected warden

Dantrolene (DTN) is a ryanodine receptor (RyR) antagonist that inhibits Ca²⁺ release from stores in the sarcoplasmic reticulum. DTN is mainly used in the management of malignant hyperthermia. RyRs are highly expressed in immune cells and are involved in different viral infections, including severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), because Ca²⁺ is necessary for viral replication, maturation and release. DTN can inhibit the proliferation of SARS-CoV-2, indicating its potential role in reducing entry and pathogenesis of SARS-CoV-2. DTN may increase clearance of SARS-CoV-2 and promote coronavirus disease 2019 (COVID-19) recovery by shortening the period of infection. DTN inhibits N-methyl-D-aspartate (NMDA) mediated platelets aggregations and thrombosis. Therefore, DTN may inhibit thrombosis and coagulopathy in COVID-19 through suppression of platelet NMDA receptors. Moreover, DTN has a neuroprotective effect against SARS-CoV-2 infection-induced brain injury through modulation of NMDA receptors, which are involved in excitotoxicity, neuronal injury and the development of neuropsychiatric disorders. In conclusion, DTN by inhibiting RyRs may attenuate inflammatory disorders in SARS-CoV-2 infection and associated cardio-pulmonary complications. Therefore, DNT could be a promising drug therapy against COVID-19. Preclinical and clinical studies are warranted in this regards.

The ORF7a protein of SARS-CoV-2 initiates autophagy and limits autophagosome-lysosome fusion via degradation of SNAP29 to promote virus replication

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is closely related to various cellular aspects associated with autophagy. However, how SARS-CoV-2 mediates the subversion of the macroautophagy/autophagy pathway remains largely unclear. In this study, we demonstrate that overexpression of the SARS-CoV-2 ORF7a protein activates LC3-II and leads to the accumulation of autophagosomes in multiple cell lines, while knockdown of the viral ORF7a gene via shRNAs targeting ORF7a sgRNA during SARS-CoV-2 infection decreased autophagy levels. Mechanistically, the ORF7a protein initiates autophagy via the AKT-MTOR-ULK1-mediated pathway, but ORF7a limits the progression of autophagic flux by activating CASP3 (caspase 3) to cleave the SNAP29 protein at aspartic acid residue 30 (D30), ultimately impairing complete autophagy. Importantly, SARS-CoV-2 infection-induced accumulated autophagosomes promote progeny virus production, whereby ORF7a downregulates SNAP29, ultimately resulting in failure of autophagosome fusion with lysosomes to promote viral replication. Taken together, our study reveals a mechanism by which SARS-CoV-2 utilizes the autophagic machinery to facilitate its own propagation via ORF7a.Abbreviations: 3-MA: 3-methyladenine; ACE2: angiotensin converting enzyme 2; ACTB/β-actin: actin beta; ATG7: autophagy related 7; Baf A1: bafilomycin A₁; BECN1: beclin 1; CASP3: caspase 3; COVID-19: coronavirus disease 2019; GFP: green fluorescent protein; hpi: hour post-infection; hpt: hour post-transfection; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MERS: Middle East respiratory syndrome; MTOR: mechanistic target of rapamycin kinase; ORF: open reading frame; PARP: poly(ADP-ribose) polymerase; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; shRNAs: short hairpin RNAs; siRNA: small interfering RNA; SNAP29: synaptosome associated protein 29; SQSTM1/p62: sequestosome 1; STX17: syntaxin 17; TCID₅₀: tissue culture infectious dose; TEM: transmission electron microscopy; TUBB, tubulin, beta; ULK1: unc-51 like autophagy activating kinase 1.

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.

Molecular signatures in the progression of COVID-19 severity

SARS-CoV-2 is the causative agent of COVID-19 that has infected over 642 million and killed over 6.6 million people around the globe. Underlying a wide range of clinical manifestations of this disease, from moderate to extremely severe systemic conditions, could be genes or pathways differentially expressing in the hosts. It is therefore important to gain insights into pathways involved in COVID-19 pathogenesis and host defense and thus understand the host response to this pathogen at the physiological and molecular level. To uncover genes and pathways involved in the differential clinical manifestations of this disease, we developed a novel gene co-expression network based pipeline that uses gene expression obtained from different SARS-CoV-2 infected human tissues. We leveraged the network to identify novel genes or pathways that likely differentially express and could be physiologically significant in the COVID-19 pathogenesis and progression but were deemed statistically non-significant and therefore not further investigated in the original studies. Our network-based approach aided in the identification of co-expression modules enriched in differentially expressing genes (DEGs) during different stages of COVID-19 and enabled discovery of novel genes involved in the COVID-19 pathogenesis, by virtue of their transcript abundance and association with genes expressing differentially in modules enriched in DEGs. We further prioritized by considering only those enriched gene modules that have most of their genes differentially expressed, inferred by the original studies or this study, and document here 7 novel genes potentially involved in moderate, 2 in severe, 48 in extremely severe COVID-19, and 96 novel genes involved in the progression of COVID-19 from severe to extremely severe conditions. Our study shines a new light on genes and their networks (modules) that drive the progression of COVID-19 from moderate to extremely severe condition. These findings could aid development of new therapeutics to combat COVID-19.

An overview of viral mutagenesis and the impact on pathogenesis of SARS-CoV-2 variants

Viruses are submicroscopic, obligate intracellular parasites that carry either DNA or RNA as their genome, protected by a capsid. Viruses are genetic entities that propagate by using the metabolic and biosynthetic machinery of their hosts and many of them cause sickness in the host. The ability of viruses to adapt to different hosts and settings mainly relies on their ability to create de novo variety in a short interval of time. The size and chemical composition of the viral genome have been recognized as important factors affecting the rate of mutations. Coronavirus disease 2019 (Covid-19) is a novel viral disease that has quickly become one of the world's leading causes of mortality, making it one of the most serious public health problems in recent decades. The discovery of new medications to cope with Covid-19 is a difficult and time-consuming procedure, as new mutations represent a serious threat to the efficacy of recently developed vaccines. The current article discusses viral mutations and their impact on the pathogenicity of newly developed variants with a special emphasis on Covid-19. The biology of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), its mutations, pathogenesis, and treatment strategies are discussed in detail along with the statistical data.

Manipulation of innate immune signaling pathways by SARS-CoV-2 non-structural proteins

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the current coronavirus disease 2019 (COVID-19) pandemic, induces an unbalanced immune response in the host. For instance, the production of type I interferon (IFN) and the response to it, which act as a front-line defense against virus invasion, are inhibited during SARS-CoV-2 infection. In addition, tumor necrosis factor alpha (TNF-α), a proinflammatory cytokine, is upregulated in COVID-19 patients with severe symptoms. Studies on the closely related betacoronavirus, SARS-CoV, showed that viral proteins such as Nsp1, Orf6 and nucleocapsid protein inhibit IFN-β production and responses at multiple steps. Given the conservation of these proteins between SARS-CoV and SARS-CoV-2, it is not surprising that SARS-CoV-2 deploys similar immune evasion strategies. Here, we carried out a screen to examine the role of individual SARS-CoV-2 proteins in regulating innate immune signaling, such as the activation of transcription factors IRF3 and NF-κB and the response to type I and type II IFN. In addition to established roles of SARS-CoV-2 proteins, we report that SARS-CoV-2 proteins Nsp6 and Orf8 inhibit the type I IFN response but at different stages. Orf6 blocks the translocation of STAT1 and STAT2 into the nucleus, whereas ORF8 inhibits the pathway in the nucleus after STAT1/2 translocation. SARS-CoV-2 Orf6 also suppresses IRF3 activation and TNF-α-induced NF-κB activation.

Autophagy in SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) orchestrates host factors to remodel endomembrane compartments for various steps of the infection cycle. SARS-CoV-2 also intimately intersects with the catabolic autophagy pathway during infection. In response to virus infection, autophagy acts as an innate defensive system by delivering viral components/particles to lysosomes for degradation. Autophagy also elicits antiviral immune responses. SARS-CoV-2, like other positive-stranded RNA viruses, has evolved various mechanisms to escape autophagic destruction and to hijack the autophagic machinery for its own benefit. In this review, we will focus on how the interplay between SARS-CoV-2 viral proteins and autophagy promotes viral replication and transmission. We will also discuss the pathogenic effects of SARS-CoV-2-elicited autophagy dysregulation and pharmacological interventions targeting autophagy for COVID-19 treatment.

Toll-like Receptor Mediation in SARS-CoV-2: A Therapeutic Approach

The innate immune system facilitates defense mechanisms against pathogen invasion and cell damage. Toll-like receptors (TLRs) assist in the activation of the innate immune system by binding to pathogenic ligands. This leads to the generation of intracellular signaling cascades including the biosynthesis of molecular mediators. TLRs on cell membranes are adept at recognizing viral components. Viruses can modulate the innate immune response with the help of proteins and RNAs that downregulate or upregulate the expression of various TLRs. In the case of COVID-19, molecular modulators such as type 1 interferons interfere with signaling pathways in the host cells, leading to an inflammatory response. Coronaviruses are responsible for an enhanced immune signature of inflammatory chemokines and cytokines. TLRs have been employed as therapeutic agents in viral infections as numerous antiviral Food and Drug Administration-approved drugs are TLR agonists. This review highlights the therapeutic approaches associated with SARS-CoV-2 and the TLRs involved in COVID-19 infection.

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.

RNA sequence analysis of nasopharyngeal swabs from asymptomatic and mildly symptomatic patients with COVID-19

OBJECTIVES

The characterization of asymptomatic and mildly symptomatic patients with COVID-19 by observing changes in gene expression profile and possible bacterial coinfection is relevant to be investigated. We aimed to identify transcriptomic and coinfection profiles in both groups of patients.

METHODS

A ribonucleic acid (RNA) sequence analysis on nasopharyngeal swabs were performed using a shotgun sequencing pipeline. Differential gene analysis, viral genome assembly, and metagenomics analysis were further performed using the retrieved data.

RESULTS

Both groups of patients underwent a cilia modification and mRNA splicing. Modulations in macroautophagy, epigenetics, and cell cycle processes were observed specifically in the asymptomatic group. Modulation in the RNA transport was found specifically in the mildly symptomatic group. The mildly symptomatic group showed modulation in the RNA transport and upregulation of autophagy regulator genes and genes in the complement system. No link between viral variants and disease severity was found. Microbiome analysis revealed the elevation of Streptococcus pneumoniae and Veillonella parvula proportion in symptomatic patients.

CONCLUSION

A reduction in the autophagy influx and modification in the epigenetic profile might be involved in halting the disease progression. A global dysregulation of RNA processing and translation might cause more severe outcomes in symptomatic individuals. Coinfection by opportunistic microflora should be taken into account when assessing the possible outcome of SARS-CoV-2 infection.

Targeting autophagy regulation in NLRP3 inflammasome-mediated lung inflammation in COVID-19

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Emerging evidence indicates that the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome is activated, which results in a cytokine storm at the late stage of COVID-19. Autophagy regulation is involved in the infection and replication of SARS-CoV-2 at the early stage and the inhibition of NLRP3 inflammasome-mediated lung inflammation at the late stage of COVID-19. Here, we discuss the autophagy regulation at different stages of COVID-19. Specifically, we highlight the therapeutic potential of autophagy activators in COVID-19 by inhibiting the NLRP3 inflammasome, thereby avoiding the cytokine storm. We hope this review provides enlightenment for the use of autophagy activators targeting the inhibition of the NLRP3 inflammasome, specifically the combinational therapy of autophagy modulators with the inhibitors of the NLRP3 inflammasome, antiviral drugs, or anti-inflammatory drugs in the fight against COVID-19.

Methodology-Centered Review of Molecular Modeling, Simulation, and Prediction of SARS-CoV-2

Despite tremendous efforts in the past two years, our understanding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), virus-host interactions, immune response, virulence, transmission, and evolution is still very limited. This limitation calls for further in-depth investigation. Computational studies have become an indispensable component in combating coronavirus disease 2019 (COVID-19) due to their low cost, their efficiency, and the fact that they are free from safety and ethical constraints. Additionally, the mechanism that governs the global evolution and transmission of SARS-CoV-2 cannot be revealed from individual experiments and was discovered by integrating genotyping of massive viral sequences, biophysical modeling of protein-protein interactions, deep mutational data, deep learning, and advanced mathematics. There exists a tsunami of literature on the molecular modeling, simulations, and predictions of SARS-CoV-2 and related developments of drugs, vaccines, antibodies, and diagnostics. To provide readers with a quick update about this literature, we present a comprehensive and systematic methodology-centered review. Aspects such as molecular biophysics, bioinformatics, cheminformatics, machine learning, and mathematics are discussed. This review will be beneficial to researchers who are looking for ways to contribute to SARS-CoV-2 studies and those who are interested in the status of the field.

Functional mutations of SARS-CoV-2: implications to viral transmission, pathogenicity and immune escape

The pandemic of coronavirus disease 2019 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to major public health challenges globally. The increasing viral lineages identified indicate that the SARS-CoV-2 genome is evolving at a rapid rate. Viral genomic mutations may cause antigenic drift or shift, which are important ways by which SARS-CoV-2 escapes the human immune system and changes its transmissibility and virulence. Herein, we summarize the functional mutations in SARS-CoV-2 genomes to characterize its adaptive evolution to inform the development of vaccination, treatment as well as control and intervention measures.

A guide to membrane atg8ylation and autophagy with reflections on immunity

The process of membrane atg8ylation, defined herein as the conjugation of the ATG8 family of ubiquitin-like proteins to membrane lipids, is beginning to be appreciated in its broader manifestations, mechanisms, and functions. Classically, membrane atg8ylation with LC3B, one of six mammalian ATG8 family proteins, has been viewed as the hallmark of canonical autophagy, entailing the formation of characteristic double membranes in the cytoplasm. However, ATG8s are now well described as being conjugated to single membranes and, most recently, proteins. Here we propose that the atg8ylation is coopted by multiple downstream processes, one of which is canonical autophagy. We elaborate on these biological outputs, which impact metabolism, quality control, and immunity, emphasizing the context of inflammation and immunological effects. In conclusion, we propose that atg8ylation is a modification akin to ubiquitylation, and that it is utilized by different systems participating in membrane stress responses and membrane remodeling activities encompassing autophagy and beyond.

Epigenetic regulation of autophagy in coronavirus disease 2019 (COVID-19)

The coronavirus disease 2019 (COVID-19) pandemic has become the most serious global public health issue in the past two years, requiring effective therapeutic strategies. This viral infection is a contagious disease caused by new coronaviruses (nCoVs), also called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Autophagy, as a highly conserved catabolic recycling process, plays a significant role in the growth and replication of coronaviruses (CoVs). Therefore, there is great interest in understanding the mechanisms that underlie autophagy modulation. The modulation of autophagy is a very complex and multifactorial process, which includes different epigenetic alterations, such as histone modifications and DNA methylation. These mechanisms are also known to be involved in SARS-CoV-2 replication. Thus, molecular understanding of the epigenetic pathways linked with autophagy and COVID-19, could provide novel therapeutic targets for COVID-19 eradication. In this context, the current review highlights the role of epigenetic regulation of autophagy in controlling COVID-19, focusing on the potential therapeutic implications.

Biologics in COVID-19 So Far: Systematic Review

This systematic review aimed to reevaluate the available evidence of the use of biologics as treatment candidates for the treatment of severe and advanced COVID-19 disease; what are the rationale for their use, which are the most studied, and what kind of efficacy measures are described? A search through Cochrane, Embase, Pubmed, Medline, medrxiv.org, and Google scholar was performed on the use of biologic interventions in COVID-19/SARS-CoV-2 infection, viral pneumonia, and sepsis, until 11 January 2022. Throughout the research, we identified 4821 records, of which 90 were selected for qualitative analysis. Amongst the results, we identified five popular targets of use: IL6 and IL1 inhibitors, interferons, mesenchymal stem cells treatment, and anti-spike antibodies. None of them offered conclusive evidence of their efficacy with consistency and statistical significance except for some studies with anti-spike antibodies; however, Il6 and IL1 inhibitors as well as interferons show encouraging data in terms of increased survival and favorable clinical course that require further studies with better methodology standardization.

Genome-Wide Analysis of the Indispensable Role of Non-structural Proteins in the Replication of SARS-CoV-2

Understanding the process of replication and transcription of SARS-CoV-2 is essential for antiviral strategy development. The replicase polyprotein is indispensable for viral replication. However, whether all nsps derived from the replicase polyprotein of SARS-CoV-2 are indispensable is not fully understood. In this study, we utilized the SARS-CoV-2 replicon as the system to investigate the role of each nsp in viral replication. We found that except for nsp16, all the nsp deletions drastically impair the replication of the replicon, and nsp14 could recover the replication deficiency caused by its deletion in the viral replicon. Due to the unsuccessful expressions of nsp1, nsp3, and nsp16, we could not draw a conclusion about their in trans-rescue functions. Our study provided a new angle to understand the role of each nsp in viral replication and transcription, helping the evaluation of nsps as the target for antiviral drug development.

In-Silico targeting of SARS-CoV-2 NSP6 for drug and natural products repurposing

Non-Structural Protein 6 (NSP6) has a protecting role for SARS-CoV-2 replication by inhibiting the expansion of autophagosomes inside the cell. NSP6 is involved in the endoplasmic reticulum stress response by binding to Sigma receptor 1 (SR1). Nevertheless, NSP6 crystal structure is not solved yet. Therefore, NSP6 is considered a challenging target in Structure-Based Drug Discovery. Herein, we utilized the high quality NSP6 model built by AlphaFold in our study. Targeting a putative NSP6 binding site is believed to inhibit the SR1-NSP6 protein-protein interactions. Three databases were virtually screened, namely FDA-approved drugs (DrugBank), Northern African Natural Products Database (NANPDB) and South African Natural Compounds Database (SANCDB) with a total of 8158 compounds. Further validation for 9 candidates via molecular dynamics simulations for 100 ns recommended potential binders to the NSP6 binding site. The proposed candidates are recommended for biological testing to cease the rapidly growing pandemic.

Evolution of SARS-CoV-2 in Spain during the First Two Years of the Pandemic: Circulating Variants, Amino Acid Conservation, and Genetic Variability in Structural, Non-Structural, and Accessory Proteins

Monitoring SARS-CoV-2’s genetic diversity and emerging mutations in this ongoing pandemic is crucial to understanding its evolution and ensuring the performance of COVID-19 diagnostic tests, vaccines, and therapies. Spain has been one of the main epicenters of COVID-19, reaching the highest number of cases and deaths per 100,000 population in Europe at the beginning of the pandemic. This study aims to investigate the epidemiology of SARS-CoV-2 in Spain and its 18 Autonomous Communities across the six epidemic waves established from February 2020 to January 2022. We report on the circulating SARS-CoV-2 variants in each epidemic wave and Spanish region and analyze the mutation frequency, amino acid (aa) conservation, and most frequent aa changes across each structural/non-structural/accessory viral protein among the Spanish sequences deposited in the GISAID database during the study period. The overall SARS-CoV-2 mutation frequency was 1.24 × 10−5. The aa conservation was >99% in the three types of protein, being non-structural the most conserved. Accessory proteins had more variable positions, while structural proteins presented more aa changes per sequence. Six main lineages spread successfully in Spain from 2020 to 2022. The presented data provide an insight into the SARS-CoV-2 circulation and genetic variability in Spain during the first two years of the pandemic.

The impact of the suppression of highly connected protein interactions on the corona virus infection

Several highly effective Covid-19 vaccines are in emergency use, although more-infectious coronavirus strains, could delay the end of the pandemic even further. Because of this, it is highly desirable to develop fast antiviral drug treatments to accelerate the lasting immunity against the virus. From a theoretical perspective, computational approaches are useful tools for antiviral drug development based on the data analysis of gene expression, chemical structure, molecular pathway, and protein interaction mapping. This work studies the structural stability of virus–host interactome networks based on the graphical representation of virus–host protein interactions as vertices or nodes connected by commonly shared proteins. These graphical network visualization methods are analogous to those use in the design of artificial neural networks in neuromorphic computing. In standard protein-node-based network representation, virus–host interaction merges with virus–protein and host–protein networks, introducing redundant links associated with the internal virus and host networks. On the contrary, our approach provides a direct geometrical representation of viral infection structure and allows the effective and fast detection of the structural robustness of the virus–host network through proteins removal. This method was validated by applying it to H1N1 and HIV viruses, in which we were able to pinpoint the changes in the Interactome Network produced by known vaccines. The application of this method to the SARS-CoV-2 virus–host protein interactome implies that nonstructural proteins nsp4, nsp12, nsp16, the nuclear pore membrane glycoprotein NUP210, and ubiquitin specific peptidase USP54 play a crucial role in the viral infection, and their removal may provide an efficient therapy. This method may be extended to any new mutations or other viruses for which the Interactome Network is experimentally determined. Since time is of the essence, because of the impact of more-infectious strains on controlling the spread of the virus, this method may be a useful tool for novel antiviral therapies.

SARS-CoV-2 non-structural protein 6 triggers NLRP3-dependent pyroptosis by targeting ATP6AP1

A recent mutation analysis suggested that Non-Structural Protein 6 (NSP6) of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a key determinant of the viral pathogenicity. Here, by transcriptome analysis, we demonstrated that the inflammasome-related NOD-like receptor signaling was activated in SARS-CoV-2-infected lung epithelial cells and Coronavirus Disease 2019 (COVID-19) patients' lung tissues. The induction of inflammasomes/pyroptosis in patients with severe COVID-19 was confirmed by serological markers. Overexpression of NSP6 triggered NLRP3/ASC-dependent caspase-1 activation, interleukin-1β/18 maturation, and pyroptosis of lung epithelial cells. Upstream, NSP6 impaired lysosome acidification to inhibit autophagic flux, whose restoration by 1α,25-dihydroxyvitamin D₃, metformin or polydatin abrogated NSP6-induced pyroptosis. NSP6 directly interacted with ATP6AP1, a vacuolar ATPase proton pump component, and inhibited its cleavage-mediated activation. L37F NSP6 variant, which was associated with asymptomatic COVID-19, exhibited reduced binding to ATP6AP1 and weakened ability to impair lysosome acidification to induce pyroptosis. Consistently, infection of cultured lung epithelial cells with live SARS-CoV-2 resulted in autophagic flux stagnation, inflammasome activation, and pyroptosis. Overall, this work supports that NSP6 of SARS-CoV-2 could induce inflammatory cell death in lung epithelial cells, through which pharmacological rectification of autophagic flux might be therapeutically exploited.

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.

Autophagy and evasion of the immune system by SARS-CoV-2. Structural features of the non-structural protein 6 from wild type and Omicron viral strains interacting with a model lipid bilayer

The viral cycle of SARS-CoV-2 is based on a complex interplay with the cellular machinery, which is mediated by specific proteins eluding or hijacking the cellular defense mechanisms. Among the complex pathways induced by the viral infection, autophagy is particularly crucial and is strongly influenced by the action of the non-structural protein 6 (Nsp6) interacting with the endoplasmic reticulum membrane. Importantly, differently from other non-structural proteins, Nsp6 is mutated in the recently emerged Omicron variant, suggesting a possible different role of autophagy. In this contribution we explore, for the first time, the structural properties of Nsp6 thanks to long-timescale molecular dynamics simulations and machine learning analysis, identifying the interaction patterns with the lipid membrane. We also show how the mutation brought by the Omicron variant may indeed modify some of the specific interactions, and more particularly help anchor the viral protein to the lipid bilayer interface.

The viral cycle of SARS-CoV-2 is based on a complex interplay with the cellular machinery, which is mediated by specific proteins eluding or hijacking the cellular defense mechanisms.

Characterization of Deltacoronavirus in Black-Headed Gulls (Chroicocephalus ridibundus) in South China Indicating Frequent Interspecies Transmission of the Virus in Birds

Deltacoronavirus (DCoV) is a genus of coronavirus (CoV) commonly found in avian and swine, but some DCoVs are capable of infecting humans, which causes the concern about interspecies transmission of DCoVs. Thus, monitoring the existence of DCoVs in animals near communities is of great importance for epidemic prevention. Black-headed gulls (Chroicocephalus ridibundus) are common migratory birds inhabiting in most urban and rural wetlands of Yunnan Province, China, which is a typical habitat for black-headed gulls to overwinter. Whether Yunnan black-headed gulls carry CoV has never been determined. In this study, we identified three strains of DCoVs in fecal samples of Yunnan black-headed gulls by reverse-transcriptional PCR and sequenced their whole genomes. Genomic analysis revealed that these three strains shared genomic identity of more than 99%, thus named DCoV HNU4-1, HNU4-2, and HNU4-3; their NSP12 showed high similarity of amino acid sequence to the homologs of falcon coronavirus UAE-HKU27 (HKU27), houbara coronavirus UAE-HKU28 (HKU28), and pigeon coronavirus UAE-HKU29 (HKU29). Since both HKU28 and HKU29 were found in Dubai, there might be cross-border transmission of these avian DCoVs through specific routes. Further coevolutionary analysis supported this speculation that HNU4 (or its ancestors) in black-headed gulls originated from HKU28 (or its homologous strain) in houbara, which was interspecies transmission between two different avian orders. In addition, interspecies transmission of DCoV, from houbara to falcon, pigeon and white-eye, from sparrow to common-magpie, and quail and mammal including porcine and Asian leopard cat, from munia to magpie-robin, was predicted. This is the first report of black-headed gull DCoV in Asia which was highly homolog to other avian DCoVs, and the very “active” host-switching events in DCoV were predicted, which provides important reference for the study of spread and transmission of DCoVs.