Study of protease-mediated processes initiating viral infection and cell-cell viral spreading of SARS-CoV-2.

Viral-cell entry and cell-cell viral spreading processes of SARS-CoV-2 are subjected to fast evolutionary optimization because of its worldwide spreading, requiring the need for new drug developments. However, this task is still challenging, because a detailed understanding of the underlying molecular processes, mediated by the key cellular proteases TMPRSS2 and furin, is still lacking. Here, we show by large-scale atomistic calculations that binding of the ACE2 cell receptor at one of the heteromers of the SARS-CoV-2 spike leads to a release of its furin cleavage site (S1/S2), enabling an enhanced furin binding, and that this latter process promotes the binding of TMPRSS2 through the release of the TMPRSS2 cleavage site (S2') out of the ACE2-binding heteromer. Moreover, we find that, after proteolytic cleavage, improved furin binding causes that parts of the S2 subunit dissociate from the complex, suggesting that furin promotes the fusion of the S2 subunit with the cell membrane before transfer of the viral RNA. Here we show by computational means that binding of the ACE2-cell receptor at one of the heteromers of the SARS-CoV-2 spike leads to an enhanced binding of the protease furin, promoting the binding of the protease TMPRSS2. Moreover, we show that, after proteolytic cleavage, improved furin binding causes that parts of the heteromer dissociate from the spike.

Peptides targeting dengue viral nonstructural protein 1 inhibit dengue virus production.

Viruses manipulate the life cycle in host cells via the use of viral properties and host machineries. Development of antiviral peptides against dengue virus (DENV) infection has previously been concentrated on blocking the actions of viral structural proteins and enzymes in virus entry and viral RNA processing in host cells. In this study, we proposed DENV NS1, which is a multifunctional non-structural protein indispensable for virus production, as a new target for inhibition of DENV infection by specific peptides. We performed biopanning assays using a phage-displayed peptide library and identified 11 different sequences of 12-mer peptides binding to DENV NS1. In silico analyses of peptide-protein interactions revealed 4 peptides most likely to bind to DENV NS1 at specific positions and their association was analysed by surface plasmon resonance. Treatment of Huh7 cells with these 4 peptides conjugated with N-terminal fluorescent tag and C-terminal cell penetrating tag at varying time-of-addition post-DENV infection could inhibit the production of DENV-2 in a time- and dose-dependent manner. The inhibitory effects of the peptides were also observed in other virus serotypes (DENV-1 and DENV-4), but not in DENV-3. These findings indicate the potential application of peptides targeting DENV NS1 as antiviral agents against DENV infection.

Human glucose-regulated protein 78 modulates intracellular production and secretion of nonstructural protein 1 of dengue virus.

Virus-host interactions play important roles in virus infection and host cellular response. Several viruses, including dengue virus (DENV), usurp host chaperones to support their amplification and survival in the host cell. We investigated the interaction of nonstructural protein 1 (NS1) of DENV with three endoplasmic reticulum-resident chaperones (i.e. GRP78, calnexin and calreticulin) to delineate their functional roles and potential binding sites for protein complex formation. GRP78 protein showed prominent association with DENV NS1 in virus-infected Huh7 cells as evidenced by co-localization and co-immunoprecipitation assays. Further studies on the functional interaction of GRP78 protein were performed by using siRNA-mediated gene knockdown in a DENV replicon transfection system. GRP78 knockdown significantly decreased intracellular NS1 production and delayed NS1 secretion but had no effect on viral RNA replication. Dissecting the important domain of GRP78 required for DENV NS1 interaction showed co-immunoprecipitation of DENV NS1 with a full-length and substrate-binding domain (SBD), but not an ATPase domain, of GRP78, confirming their interaction through SBD binding. Molecular dynamics simulations of DENV NS1 and human GRP78 complex revealed their potential binding sites through hydrogen and hydrophobic bonding. The majority of GRP78-binding sites were located in a ß-roll domain and connector subdomains on the DENV NS1 structure involved in hydrophobic surface formation. Taken together, our findings demonstrated the roles of human GRP78 in facilitating the intracellular production and secretion of DENV NS1 as well as predicted potential binding sites between the DENV NS1 and GRP78 complex, which could have implications in the future development of target-based antiviral drugs.