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.

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† † Electronic supplementary information (ESI) available: Analysis of the secondary structure of the protein and the specific lipid/amino acid interactions. RMSF per amino acid. Distribution of the distance between the center of mass of the 89 to 99 α-helix and the center of the lipid bilayer. Analysis of the behavior of the 195 to 207 α-helix. See https://doi.org/10.1039/d2sc00108j

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.

Never Cared for What They Do: High Structural Stability of Guanine-Quadruplexes in the Presence of Strand-Break Damage

DNA integrity is an important factor that assures genome stability and, more generally, the viability of cells and organisms. In the presence of DNA damage, the normal cell cycle is perturbed when cells activate their repair processes. Although efficient, the repair system is not always able to ensure complete restoration of gene integrity. In these cases, mutations not only may occur, but the accumulation of lesions can either lead to carcinogenesis or reach a threshold that induces apoptosis and programmed cell death. Among the different types of DNA lesions, strand breaks produced by ionizing radiation are the most toxic due to the inherent difficultly of repair, which may lead to genomic instability. In this article we show, by using classical molecular simulation techniques, that compared to canonical double-helical B-DNA, guanine-quadruplex (G4) arrangements show remarkable structural stability, even in the presence of two strand breaks. Since G4-DNA is recognized for its regulatory roles in cell senescence and gene expression, including oncogenes, this stability may be related to an evolutionary cellular response aimed at minimizing the effects of ionizing radiation.

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.

Role of RNA Guanine Quadruplexes in Favoring the Dimerization of SARS Unique Domain in Coronaviruses.

Coronaviruses may produce severe acute respiratory syndrome (SARS). As a matter of fact, a new SARS-type virus, SARS-CoV-2, is responsible for the global pandemic in 2020 with unprecedented sanitary and economic consequences for most countries. In the present contribution we study, by all-atom equilibrium and enhanced sampling molecular dynamics simulations, the interaction between the SARS Unique Domain and RNA guanine quadruplexes, a process involved in eluding the defensive response of the host thus favoring viral infection of human cells. Our results evidence two stable binding modes involving an interaction site spanning either the protein dimer interface or only one monomer. The free energy profile unequivocally points to the dimer mode as the thermodynamically favored one. The effect of these binding modes in stabilizing the protein dimer was also assessed, being related to its biological role in assisting the SARS viruses to bypass the host protective response. This work also constitutes a first step in the possible rational design of efficient therapeutic agents aiming at perturbing the interaction between SARS Unique Domain and guanine quadruplexes, hence enhancing the host defenses against the virus.

Molecular Basis of SARS-CoV-2 Infection and Rational Design of Potential Antiviral Agents: Modeling and Simulation Approaches.

The emergence in late 2019 of the coronavirus SARS-CoV-2 has resulted in the breakthrough of the COVID-19 pandemic that is presently affecting a growing number of countries. The development of the pandemic has also prompted an unprecedented effort of the scientific community to understand the molecular bases of the virus infection and to propose rational drug design strategies able to alleviate the serious COVID-19 morbidity. In this context, a strong synergy between the structural biophysics and molecular modeling and simulation communities has emerged, resolving at the atomistic level the crucial protein apparatus of the virus and revealing the dynamic aspects of key viral processes. In this Review, we focus on how in silico studies have contributed to the understanding of the SARS-CoV-2 infection mechanism and the proposal of novel and original agents to inhibit the viral key functioning. This Review deals with the SARS-CoV-2 spike protein, including the mode of action that this structural protein uses to entry human cells, as well as with nonstructural viral proteins, focusing the attention on the most studied proteases and also proposing alternative mechanisms involving some of its domains, such as the SARS unique domain. We demonstrate that molecular modeling and simulation represent an effective approach to gather information on key biological processes and thus guide rational molecular design strategies.