Screening and identifying natural products with SARS-CoV-2 infection inhibitory activity from medicinal fungi

The coronavirus disease of 2019(COVID‐19),a global pandemic caused by the severe acute respiratory syndrome coronavirus 2(SARS‐CoV‐2),can result in severe health complications.In addition to physical preventative measures,pharmaceutical intervention is also crucial.Numerous natural products from medicinal fungi have shown promise as potential antiviral drugs and may serve as a source of effective components with antiviral activity against SARS‐CoV‐2 and other coronaviruses.In this study,we developed a workflow that integrates viral infection inhibition assays at both cellular and molecular levels,as well as molecular separation and characterization,to screen and identify natural products with antiviral activity.Using this workflow,we screened 167 extracts extracted from 36 medicinal fungi using optimized extraction methods.We assessed the antiviral effects of these extracts by measuring their ability to inhibit SARS‐CoV‐2 infection and receptor binding domain‐human angiotensin‐converting enzyme 2(RBD‐hACE2)binding in vitro.Following charge‐and size‐based characterization of the active compounds through filtration and chromatographic fractionation,mass spectrometry characterization of the fractionated compounds revealed that the active components are polysaccharides and determined their monosaccharide residue composition.Our findings provide new insights into the antiviral potential of natural products and their screening strategies and may contribute to the development of effective antiviral therapeutics against COVID‐19 and other diseases.

Identification of potential cross-protective epitope between a new type of coronavirus(2019-nCoV)and severe acute respiratory syndrome virus

Recently,a new type of unknown virus causing severe acute res-piratory infection was reported in Wuhan city,Hubei province,China(WHO,2020b).Infection of this virus was first reported in December 2019,and origin of the virus was traced back to a large seafood/wide animal market in Wuhan city.The serious clinical symptoms of the viral infection,including fever,dry cough,dys-pnea,and pneumonia,may result in progressive respiratory failure and even death.Moreover,the quick spread of the virus has caused an epidemic in China,as well as infection cases worldwide.The whole-genome sequence of Wuhan new virus(WH-Human_.1)was first released on January 10,2020(Zhang,2020),followed by additional ones released in Global Initiative on Sharing All Influ-enza Data(GISAID)(Shu and McCauley,2017).Later,this new virus was determined and announced as a new type of coronavirus(CoV;2019-nCoV)by the World Health Organization(WHO,2020a).

SARS-CoV-2 nsp12 attenuates type Ⅰ interferon production by inhibiting IRF3 nuclear translocation

SARS-CoV-2 is the pathogenic agent of COVID-19,which has evolved into a global pandemic.Compared with some other respiratory RNA viruses,SARS-CoV-2 is a poor inducer of type Ⅰ interferon(IFN).Here,we report that SARS-CoV-2 nsp12,the viral RNA-dependent RNA polymerase(RdRp),suppresses host antiviral responses.SARS-CoV-2 nsp12 attenuated Sendai virus(SeV)-or poly(I:C)-induced IFN-β promoter activation in a dose-dependent manner.It also inhibited IFN promoter activation triggered by RIG-I,MDA5,MAVS,and IRF3 overexpression.Nsp12 did not impair IRF3 phosphorylation but suppressed the nuclear translocation of IRF3.Mutational analyses suggested that this suppression was not dependent on the polymerase activity of nsp12.Given these findings,our study reveals that SARS-CoV-2 RdRp can antagonize host antiviral innate immunity and thus provides insights into viral pathogenesis.

Seroprevalence of Wenzhou virus in China

Wenzhou virus(WENV)was first identified in rodents and Asian house shrews in Wenzhou,Zhejiang Province,China.However,little is known about the prevalence of WENV infections in humans in China.To determine the threat that WENV may pose to humans,we determine the seroprevalence of WENV in healthy individuals in China in this study.Cross-reactivities of nucleoprotein(NP)were detected between Lymphocytic choriomeningitis virus(LCMV)and WENV using Western blot and ELISA assy.The prevalence of specific IgG antibodies against WENV NP was investigated in different age groups of 830 healthy individuals aged 0-70 years old in China using a competition ELISA assay.The results indicate that WENV and LCMV share cross-reactive epitopes between NPs.The total seroprevalence of WENV in healthy adults was 4.6%,with 3.6%(8/221)for individuals 15-44 years of age,5.4%(17/317)for individuals 45-59 years of age,and 4.1%(4/98)for older adults over 60.The total seroprevalence of WENV in children under age 15 was 1.5%,with 2.9%(1/34)in children aged 2-5 years,and 2.2%in 5-14 years(2/91).The finding suggests that WENV or WENV-like virus may sporadically infect humans of China.

Genome-wide CRISPR activation screen identifies candidate receptors for SARS-CoV-2 entry

The outbreak of coronavirus disease 2019(COVID-19) caused by SARS-CoV-2 has created a global health crisis. SARS-CoV-2 infects varieties of tissues where the known receptor ACE2 is low or almost absent, suggesting the existence of alternative viral entry pathways. Here, we performed a genome-wide barcoded-CRISPRa screen to identify novel host factors that enable SARS-CoV-2 infection. Beyond known host proteins, i.e., ACE2, TMPRSS2, and NRP1, we identified multiple host components,among which LDLRAD3, TMEM30A, and CLEC4G were confirmed as functional receptors for SARS-CoV-2. All these membrane proteins bind directly to spike’s N-terminal domain(NTD). Their essential and physiological roles have been confirmed in either neuron or liver cells. In particular, LDLRAD3 and CLEC4G mediate SARS-CoV-2 entry and infection in an ACE2-independent fashion. The identification of the novel receptors and entry mechanisms could advance our understanding of the multiorgan tropism of SARS-CoV-2, and may shed light on the development of COVID-19 countermeasures.

Sensing of cytoplasmic chromatin by cGAS activates innate immune response in SARS-CoV-2 infection

The global coronavirus disease 2019(COVID-19)pandemic is caused by severe acute respiratory syndrome coronavirus 2(SARSCoV-2),a positive-sense RNA virus.How the host immune system senses and responds to SARS-CoV-2 infection remain largely unresolved.Here,we report that SARS-CoV-2 infection activates the innate immune response through the cytosolic DNA sensing cGAS-STING pathway.SARS-CoV-2 infection induces the cellular level of 2′3′-cGAMP associated with STING activation.cGAS recognizes chromatin DNA shuttled from the nucleus as a result of cell-to-cell fusion upon SARS-CoV-2 infection.We further demonstrate that the expression of spike protein from SARS-CoV-2 and ACE2 from host cells is sufficient to trigger cytoplasmic chromatin upon cell fusion.Furthermore,cytoplasmic chromatin-cGAS-STING pathway,but not MAVS-mediated viral RNA sensing pathway,contributes to interferon and pro-inflammatory gene expression upon cell fusion.Finally,we show that cGAS is required for host antiviral responses against SARS-CoV-2,and a STING-activating compound potently inhibits viral replication.Together,our study reported a previously unappreciated mechanism by which the host innate immune system responds to SARS-CoV-2 infection,mediated by cytoplasmic chromatin from the infected cells.Targeting the cytoplasmic chromatin-cGAS-STING pathway may offer novel therapeutic opportunities in treating COVID-19.In addition,these findings extend our knowledge in host defense against viral infection by showing that host cells’self-nucleic acids can be employed as a“danger signal”to alarm the immune system.

Voice from China:nomenclature of the novel coronavirus and related diseases

Since early December 2019,the novel coronavirus has caused an outbreak of pneumonia that has claimed over 2000 lives,with more than 77,000 confirmed cases of infection by February 23,2020 in China.[1]The World Health Organization(WHO)recently named the disease caused by this new coronavirus as"coronavirus disease 2019(COVID-19)".The International Committee on Taxonomy of Viruses(ICTV)has named the new virus"severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)".[2]However,questions have been raised by different academic and professional bodies regarding whether the nomenclature is appropriate.