SARS-CoV-2 NSP12 associates with TRiC and the P323L substitution acts as a host adaption

The effect of molnupiravir and nirmatrelvir on SARS-CoV-2 genome diversity in severe models of COVID-19

Immunocompromised individuals are susceptible to severe coronavirus disease 2019 and potentially contribute to the emergence of variants with altered pathogenicity due to persistent infection. This study investigated the impact of immunosuppression on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in K18-hACE2 mice and the effectiveness of antiviral treatments in this context during the first 7 days of infection. Mice were immunosuppressed using cyclophosphamide and infected with a B lineage of SARS-CoV-2. Molnupiravir and nirmatrelvir, alone and in combination, were administered, and viral load and viral sequence diversity were assessed. Treatment of infected but immunocompromised mice with both compounds either singly or in combination resulted in decreased viral loads and pathological changes compared to untreated animals. Treatment also abrogated infection of neuronal tissue. However, no consistent changes in the viral consensus sequence were observed, except for the emergence of the S:H655Y mutation. Molnupiravir, but not nirmatrelvir or immunosuppression alone, increased the transition/transversion ratio, representative of G > A and C > U mutations, and this increase was not altered by the co-administration of nirmatrelvir with molnupiravir. Notably, immunosuppression itself did not appear to promote the emergence of mutational characteristics of variants of concern (VOCs). Further investigations are warranted to fully understand the role of immunocompromised individuals in VOC development, especially by taking persistence into consideration, and to inform optimized public health strategies. It is more likely that immunodeficiency promotes viral persistence but does not necessarily lead to substantial consensus-level changes in the absence of antiviral selection pressure. Consistent with mechanisms of action, molnupiravir showed a stronger mutagenic effect than nirmatrelvir in this model.

IMPORTANCE

The central aim of this study was to risk-assess the impact of administering a mutagenic antiviral compound, molnupiravir, to patients believed to already be at risk of generating increased viral diversity, which could have severe implications for antiviral resistance development. Combination therapy has a long history of mitigating antiviral resistance risk and was used in this study to demonstrate its potential usefulness in a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) context. Animals treated with molnupiravir showed an increase in transition/transversion ratios over time, consistent with the drug's mechanism of action and a recent UK-wide phase II clinical trial assessing the efficacy of molnupiravir in humans. The addition of nirmatrelvir increased viral clearance, which in turn reduces the probability of viral persistence and rapid intra-host evolution of SARS-CoV-2.

Protein folding by the CCT/TRiC chaperone complex

The chaperonin-containing TCP-1 (CCT) complex, also known as TRiC, is an abundant and essential molecular chaperone responsible for folding a significant portion of the eukaryotic proteome. Prominent CCT folding clients include cytoskeletal proteins such as actin and tubulin, and proteins with β-propeller folds. Recent advances in cryo-EM have provided unprecedented insights into CCT's substrate-specific folding mechanisms. This review summarizes these discoveries, emphasizing how CCT utilizes its unique structural features to recognize and fold diverse substrates.

Linking the function of cis-acting RNA elements to coronavirus replication using interactomes

RNA structures that are functionally important are defined as cis-acting RNA elements because their functions cannot be compensated for in trans. The cis-acting RNA elements in the 3' UTR of coronaviruses are important for replication; however, the mechanism linking the cis-acting RNA elements to their replication function remains to be established. In the present study, a comparison of the biological processes of the interactome and the replication efficiency between the 3' UTR cis-acting RNA elements in coronaviruses, including severe acute respiratory syndrome coronavirus 2, suggests that (i) the biological processes, including translation, protein folding and protein stabilization, derived from the analysis of the cis-acting RNA element interactome and (ii) the architecture of the cis-acting RNA elements and their interactomes are highly correlated with coronavirus replication. In addition, alteration of the interactome using the compound 5-benzyloxygramine can cause reduced coronavirus replication, reinforcing the connection between cis-acting RNA elements and replication by interactome. Together, these results link cis-acting RNA elements to the coronavirus replication and establish a model to analyse the cis-acting RNA elements in the replication of RNA viruses by interactome.

The effect of molnupiravir and nirmatrelvir on SARS-CoV-2 genome diversity in severe models of COVID-19

Objectives

Immunocompromised individuals are susceptible to severe COVID-19 and potentially contribute to the emergence of variants with altered pathogenicity due to persistent infection. This study investigated the impact of immunosuppression on SARS-CoV-2 infection in k18-hACE2 mice and the effectiveness of antiviral treatments in this context during the first 7 days of infection.

Methods

Mice were immunosuppressed using cyclophosphamide and infected with a B daughter lineage of SARS-CoV-2. Molnupiravir and nirmatrelvir, alone and in combination, were administered and viral load and viral sequence diversity was assessed.

Results

Treatment of infected but immune compromised mice with both compounds either singly or in combination resulted in decreased viral loads and pathological changes compared to untreated animals. Treatment also abrogated infection of neuronal tissue. However, no consistent changes in the viral consensus sequence were observed, except for the emergence of the S:H655Y mutation. Molnupiravir, but not nirmatrelvir or immunosuppression alone, increased the transition/transversion (Ts/Tv) ratio, representative of G>A and C>U mutations and this increase was not altered by the co-administration of nirmatrelvir with molnupiravir.Notably, immunosuppression itself did not appear to promote the emergence of mutational characteristic of variants of concern (VOCs).

Conclusions

Further investigations are warranted to fully understand the role of immunocompromised individuals in VOC development, especially by taking persistence into consideration, and to inform optimised public health strategies. It is more likely that immunodeficiency promotes viral persistence but does not necessarily lead to substantial consensus-level changes in the absence of antiviral selection pressure. Consistent with mechanisms of action, molnupiravir showed a stronger mutagenic effect than nirmatrelvir in this model.

Comparative Proteomics and Interactome Analysis of the SARS-CoV-2 Nucleocapsid Protein in Human and Bat Cell Lines

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of COVID-19 and responsible for the global coronavirus pandemic which started in 2019. Despite exhaustive efforts to trace its origins, including potential links with pangolins and bats, the precise origins of the virus remain unclear. Bats have been recognized as natural hosts for various coronaviruses, including the Middle East respiratory coronavirus (MERS-CoV) and the SARS-CoV. This study presents a comparative analysis of the SARS-CoV-2 nucleocapsid protein (N) interactome in human and bat cell lines. We identified approximately 168 cellular proteins as interacting partners of SARS-CoV-2 N in human cells and 196 cellular proteins as interacting partners with this protein in bat cells. The results highlight pathways and events that are both common and unique to either bat or human cells. Understanding these interactions is crucial to comprehend the reasons behind the remarkable resilience of bats to viral infections. This study provides a foundation for a deeper understanding of host-virus interactions in different reservoirs.