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Simnotrelvir has in vitro activity against SARS-CoV-2. In this phase 2–3 trial in China, simnotrelvir given within 72 hours after symptom onset led to symptom resolution approximately 36 hours faster than placebo.

Deaths caused by coronavirus disease 2019 (COVID-19) are largely due to the lungs edema resulting from the disruption of the lung alveolo-capillary barrier, induced by SARS-CoV-2-triggered pulmonary cell apoptosis. However, the molecular mechanism underlying the proapoptotic role of SARS-CoV-2 is still unclear. Here, we revealed that SARS-CoV-2 membrane (M) protein could induce lung epithelial cells mitochondrial apoptosis. Notably, M protein stabilized B-cell lymphoma 2 (BCL-2) ovarian killer (BOK) via inhibiting its ubiquitination and promoted BOK mitochondria translocation. The endodomain of M protein was required for its interaction with BOK. Knockout of BOK by CRISPR/Cas9 increased cellular resistance to M protein-induced apoptosis. BOK was rescued in the BOK-knockout cells, which led to apoptosis induced by M protein. M protein induced BOK to trigger apoptosis in the absence of BAX and BAK. Furthermore, the BH2 domain of BOK was required for interaction with M protein and proapoptosis. In vivo M protein recombinant lentivirus infection induced caspase-associated apoptosis and increased alveolar-capillary permeability in the mouse lungs. BOK knockdown improved the lung edema due to lentivirus-M protein infection. Overall, M protein activated the BOK-dependent apoptotic pathway and thus exacerbated SARS-CoV-2 associated lung injury in vivo. These findings proposed a proapoptotic role for M protein in SARS-CoV-2 pathogenesis, which may provide potential targets for COVID-19 treatments.In SARS-CoV-2-infected lung epithelial cells, endodomain of M protein binds to the BH2 domain of BOK and inhibits ubiquitination. BOK is stabilized and translocate to the mitochondrial outer membrane, promoting Cyt c release. Cyt c released outside the mitochondria activates CASP 9 mediated apoptosis, thereby inducing pulmonary edema.

The pandemic of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has caused a public health emergency, and research on the development of various types of vaccines is rapidly progressing at an unprecedented development speed internationally. Some vaccines have already been approved for emergency use and are being supplied to people around the world, but there are still many ongoing efforts to create new vaccines. Virus-like particles (VLPs) enable the construction of promising platforms in the field of vaccine development. Here, we demonstrate that non-infectious SARS-CoV-2 VLPs can be successfully assembled by co-expressing three important viral proteins membrane (M), envelop (E) and nucleocapsid (N) in plants. Plant-derived VLPs were purified by sedimentation through a sucrose cushion. The shape and size of plant-derived VLPs are similar to native SARS-CoV-2 VLPs without spike. Although the assembled VLPs do not have S protein spikes, they could be developed as formulations that can improve the immunogenicity of vaccines including S antigens, and further could be used as platforms that can carry S antigens of concern for various mutations.

Objective The purpose of this study was to identify the M protein trans-acting positive regulator (Mga) orthologue and its adjacent M-like protein (SCM) alleles in Streptococcus canis . Results Using the 39 SCM allele isolates and polymerase chain reaction-based amplification and sequencing, we obtained the deduced Mga amino acid (AA) sequences. The 22 Mga sequences in whole-genome sequences were obtained by searching the National Collection of Type Cultures 12,191(T) Mga sequence into the database. The percentage identity to the type-strain Mga sequence was examined along with its size. The presence of the Mga-specific motifs was confirmed. Of the 62 strains, we identified 59 Mga sequences with an AA size of 509 (except for four different sizes). Percentage identity ranged from 96.66 to 100% with the confirmed Mga-specific motifs and diverse SCM allele populations. Our findings support the presence of an Mga orthologue and diverse SCM allele populations.

Severe Acute Respiratory Syndrome CoronaVirus-2 (SARS-CoV-2) is composed of four structural proteins and several accessory non-structural proteins. SARS-CoV-2’s most abundant structural protein, Membrane (M) protein, has a pivotal role both during viral infection cycle and host interferon antagonism. This is a highly conserved viral protein, thus an interesting and suitable target for drug discovery. In this paper, we explain the structural nature of M protein homodimer. To do so, we developed and applied a detailed and robust in silico workflow to predict M protein dimeric structure, membrane orientation, and interface characterization. Single Nucleotide Polymorphisms (SNPs) in M protein were retrieved from over 1.2 M SARS-CoV-2 genomes and proteins from the Global Initiative on Sharing All Influenza Data (GISAID) database, 91 of which were located at the predicted dimer interface. Among those, we identified SNPs in Variants of Concern (VOC) and Variants of Interest (VOI). Binding free energy differences were evaluated for dimer interfacial SNPs to infer mutant protein stabilities. A few high-prevalent mutated residues were found to be especially relevant in VOC and VOI. This realization may be a game-changer to structure-driven formulation of new therapeutics for SARS-CoV-2.

The membrane protein M of the Porcine Epidemic Diarrhea Virus (PEDV) is the most abundant component of the viral envelope. The M protein plays a central role in the morphogenesis and assembly of the virus through protein interactions of the M-M, M-Spike (S) and M-nucleocapsid (N) type. The M protein is known to induce protective antibodies in pigs and to participate in the antagonistic response of the cellular antiviral system coordinated by the type I and type III interferon pathways. The 3D structure of the PEDV M protein is still unknown. The present work exposes a predicted 3D model of the M protein generated using the Robetta protocol. The M protein model is organized into a transmembrane and a globular region. The obtained 3D model of the PEDV M protein was compared with 3D models of the SARS-CoV-2 M protein created using neural networks and with initial machine learning-based models created using trRosetta. The 3D model of the present study predicted four linear B-cell epitopes (RSVNASSGTG and KHGDYSAVSNPSALT peptides are noteworthy), six discontinuous B-cell epitopes, forty weak binding and fourteen strong binding T-cell epitopes in the CV777 M protein. A high degree of conservation of the epitopes predicted in the PEDV M protein was observed among different PEDV strains isolated in different countries. The data suggest that the M protein could be a potential candidate for the development of new treatments or strategies that activate protective cellular mechanisms against viral diseases.

Virus-like particles (VLPs) offer potentially high-immunogenicity/low-cost vaccine platforms. SARS-CoV-2 VLPs production is achieved via transient transfection of genes encoding viral structural proteins, but is costly and difficult to scale up. To address this problem, stable VLPs-producing cell lines are desirable. In this study, we achieved efficient VLPs production by HEK293T cells after transient transfection of four plasmids containing the S, M, N, and E genes with optimized codons. Moreover, spike-specific IgG antibodies were elicited in mice, though no significant neutralizing activity was detected at the tested time points. Transmission electron microscopy (TEM) revealed that the VLPs diameters were approximately 120 nm. However, overexpression of E or M proteins was toxic to the cells. Stable cell lines were established by constructing two plasmids, in which E and M expression was controlled by an inducible Tet-on promoter and they were placed adjacent to S and N, respectively. A HEK293T cell line for stable expression of SARS-CoV-2 VLPs was established by co-selection with two antibiotics, puromycin and blasticidin. Specific IgG antibodies against the S protein were detected in mice immunized with VLPs formulated with the alum adjuvant. Our findings provide an effective approach for large-scale production of SARS-CoV-2 VLPs as vaccine candidates.

Group A Streptococcus (Strep A) causes both uncomplicated and severe invasive infections, as well as the post-infection complications acute rheumatic fever and rheumatic heart disease. Despite the high global burden of disease resulting from Strep A infections, there is not a licensed vaccine. A 30-valent M protein-based vaccine has previously been shown to be immunogenic in animal models and in a Phase I clinical trial (NCT02564237). Here, we assessed the immunogenicity of a 30-valent messenger (m)RNA vaccine designed to express the same M peptide targets as the 30-valent protein vaccine and compared it with the protein vaccine. Female New Zealand white rabbits were immunized with one of four vaccine formulations (3 doses of each formulation at days 1, 28, and 56): soluble mRNA (100 μg/animal), C-terminal transmembrane mRNA (100 μg/animal), protein vaccine (400 μg/animal), or a non-translatable RNA control (100 μg/animal). Serum was collected one day prior to the first dose and on days 42 and 70. Rabbit serum samples were assayed for antibody levels against synthetic M peptides by ELISA. HL-60 opsonophagocytic killing (OPK) assays were performed to assess functional antibody levels. Serum IgG levels were similar for the mRNA and protein vaccines. The CtTM version of the mRNA vaccine elicited slightly higher antibody levels than the mRNA designed to express soluble proteins. OPK activity was similar for the mRNA and protein vaccines, regardless of M type. The total antibody responses and functional antibody levels elicited by the 30-valent mRNA Strep A vaccines were similar to those observed following immunization with the analogous protein vaccine. The mRNA vaccine platform provides potential advantages to protein-based vaccines including inherent adjuvant activity, increased production efficiency, lower cost, and the potential to rapidly change epitopes/peptides, all of which are important considerations related to multivalent Strep A vaccine development.

SARS-CoV-2 is a highly transmissible virus that causes COVID-19 disease. Mechanisms of viral pathogenesis include excessive inflammation and viral-induced cell death, resulting in tissue damage. Here we show that the host E3-ubiquitin ligase TRIM7 acts as an inhibitor of apoptosis and SARS-CoV-2 replication via ubiquitination of the viral membrane (M) protein. Trim7 -/- mice exhibit increased pathology and virus titers associated with epithelial apoptosis and dysregulated immune responses. Mechanistically, TRIM7 ubiquitinates M on K14, which protects cells from cell death. Longitudinal SARS-CoV-2 sequence analysis from infected patients reveal that mutations on M-K14 appeared in circulating variants during the pandemic. The relevance of these mutations was tested in a mouse model. A recombinant M-K14/K15R virus shows reduced viral replication, consistent with the role of K15 in virus assembly, and increased levels of apoptosis associated with the loss of ubiquitination on K14. TRIM7 antiviral activity requires caspase-6 inhibition, linking apoptosis with viral replication and pathology. TRIM7 acts as an antiviral factor during SARS-CoV-2 infection, by ubiquitinating the M protein on K14 and inhibiting caspase-6-dependent apoptosis. The natural K14 mutations in circulating strains support the physiological role of M ubiquitination.

We have previously shown that the hepatitis C virus (HCV) E1E2 envelope glycoprotein can regulate HIV-1 long-terminal repeat (LTR) activity through disruption to NF-κB activation. This response is associated with upregulation of the endoplasmic reticulum (ER) stress response pathway. Here, we demonstrate that the SARS-CoV-2 S, M, and E but not the N structural protein can perform similar downmodulation of HIV-1 LTR activation, and in a dose-dependent manner, in both HEK293 and lung BEAS-2B cell lines. This effect is highest with the SARS-CoV-2 Wuhan S strain and decreases over time for the subsequent emerging variants of concern (VOC), with Omicron providing the weakest effect. We developed pseudo-typed viral particle (PVP) viral tools that allowed for the generation of cell lines constitutively expressing the four SARS-CoV-2 structural proteins and utilising the VSV-g envelope protein to deliver the integrated gene construct. Differential gene expression analysis (DGEA) was performed on cells expressing S, E, M, or N to determine cell activation status. Gene expression differences were found in a number of interferon-stimulated genes (ISGs), including IF16, IFIT1, IFIT2, and ISG15, as well as for a number of heat shock protein (HSP) genes, including HSPH1, HSPA6, and HSPBP1, with all four SARS-CoV-2 structural proteins. There were also differences observed in expression patterns of transcription factors, with both SP1 and MAVS upregulated in the presence of S, M, and E but not the N protein. Collectively, the results indicate that gene expression patterns associated with ER stress pathways can be activated by SARS-CoV-2 envelope glycoprotein expression. The results suggest the SARS-CoV-2 infection can modulate an array of cell pathways, resulting in disruption to NF-κB signalling, hence providing alterations to multiple physiological responses of SARS-CoV-2-infected cells.