N501Y mutation of spike protein in SARS-CoV-2 strengthens its binding to receptor ACE2

Strand displacement-enhanced CRISPR-Cas13a system for ultra-specific detection of RNA single nucleotide variation

RNA plays a critical role in biological systems, mediating genetic information transfer and regulating gene expression. However, RNA is susceptible to variations from endogenous and exogenous sources, with potentially profound biological consequences. The CRISPR-Cas13a system has emerged as a promising tool for RNA variation detection due to its cost-effectiveness, sensitivity, and user-friendly nature. Despite this, designing a simple, universal system with high discrimination factor (DF) for single-nucleotide variations remains a challenge. Here, we present the strand displacement-enhanced Cas13a single-nucleotide variation detection assay (SECND), a sensitive, universal, and easy-to-implement method with a high DF for RNA variations. Using SECND, we detected 5 types of single-nucleotide variations, achieving a maximum DF of 1083.2. We validated the assay's effectiveness on miRNA and SARS-CoV-2 genomic RNA simulants, incorporating a 4-way strand displacement mechanism to enhance detection limits to 10 pmol/L and 50 pmol/L, and to identify variations at frequencies as low as 0.01 % and 0.1 %. Additionally, we demonstrated SECND's utility in quantifying single-nucleotide variants of miR-200b and miR-200c in ovarian cancer and retinal glioma cells. This versatile tool not only advances RNA variation detection but also has significant implications for disease research, diagnostics, and viral classification, enhancing our understanding of the CRISPR-Cas13a system and its potential applications.

SARS-CoV-2 spike protein: structure, viral entry and variants

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been a devastating global pandemic for 4 years and is now an endemic disease. With the emergence of new viral variants, COVID-19 is a continuing threat to public health despite the wide availability of vaccines. The virus-encoded trimeric spike protein (S protein) mediates SARS-CoV-2 entry into host cells and also induces strong immune responses, making it an important target for development of therapeutics and vaccines. In this Review, we summarize our latest understanding of the structure and function of the SARS-CoV-2 S protein, the molecular mechanism of viral entry and the emergence of new variants, and we discuss their implications for development of S protein-related intervention strategies.

Substitution-Mutation Rate Ratio (c/µ) As Molecular Adaptation Test Beyond Ka/Ks: A SARS-COV-2 Case Study

The Ka/Ks ratio test, which assesses nonsynonymous versus synonymous substitution rates in Translated Region (TR) of a genome, is widely used to quantify fitness changes due to mutations but its critical limits are to be addressed. Ka/Ks can categorize the total fitness change as neutral (Ka/Ks = 1), beneficial (Ka/Ks > 1), or deleterious (Ka/Ks < 1), only if synonymous mutations are neutral. Otherwise, Ka/Ks only provides the fitness change due to protein sequence change. This neutrality assumption also renders this test inapplicable to sites in non-protein-coding UnTranslated Region (UTR). Our previous work introduced a substitution-mutation rate ratio (c/µ) per nucleotide site test (c: substitution rate in UTR/TR or a mean value of Ka and Ks in TR; and µ: mutation rate) as a generalized alternative to detect selection pressure, offering a broader application without forementioned presumptions. This paper derives a general equation linking c/µ with weighted Ks/µ and Ka/µ (c/µ = Ps*(Ks/μ) + Pa*(Ka/μ), Ps and Pa: proportions of synonymous and nonsynonymous sites under a mutation model and a codon table), demonstrating that Ka/Ks infers the same fitness change as c/µ does only if synonymous mutations are neutral (i.e. Ks/µ = 1). Otherwise, Ka/Ks might provide a different assignment from the c/µ test. Indeed, our comparative analysis of the c/µ and Ka/Ks tests across 25 proteins of SARS-COV-2 using three independent genomic sequence datasets shows that Ka/Ks inaccurately reports the type of fitness change for 7 proteins. Our findings advocate for the c/µ test to complement traditional Ka/Ks test to detect the selection pressure at a nucleotide site in a genome.

Impact of SARS-CoV-2 RBM Mutations N501Y and E484K on ACE2 Binding: A Combined Computational and Experimental Study

The SARS-CoV-2 spike receptor-binding motif is crucial for viral entry via interaction with the human ACE2 receptor. Mutations N501Y and E484K, found in several variants of concern, impact viral transmissibility and immune escape, but experimental data on their binding effects remain inconsistent. Using isothermal titration calorimetry (ITC) and molecular dynamics (MD) simulations, we analyzed the thermodynamic and structural effects of these mutations. ITC confirmed that N501Y increases ACE2 affinity by 2.2-fold, while E484K enhances binding by 5.8-fold. The Beta/Gamma variant (carrying both mutations) showed the strongest affinity, with a 15-fold increase. E484K was enthalpy-driven, while N501Y introduced entropy-driven effects, suggesting hydrophobic interactions and conformational changes. MD simulations revealed distinct binding poses, with Beta/Gamma peptides interacting with a secondary ACE2 site. A strong correlation was found between entropy contributions and hydrophobic contacts. Additionally, a convolutional neural network was used to estimate the free binding energy of these complexes. Our findings confirm that N501Y and E484K enhance ACE2 binding, with the greatest effect when combined, providing insights into SARS-CoV-2 variant evolution and potential therapeutic strategies.

Beyond the Pandemic Era: Recent Advances and Efficacy of SARS-CoV-2 Vaccines Against Emerging Variants of Concern

Vaccination has been instrumental in curbing the transmission of SARS-CoV-2 and mitigating the severity of clinical manifestations associated with COVID-19. Numerous COVID-19 vaccines have been developed to this effect, including BioNTech-Pfizer and Moderna's mRNA vaccines, as well as adenovirus vector-based vaccines such as Oxford-AstraZeneca. However, the emergence of new variants and subvariants of SARS-CoV-2, characterized by enhanced transmissibility and immune evasion, poses significant challenges to the efficacy of current vaccination strategies. In this review, we aim to comprehensively outline the landscape of emerging SARS-CoV-2 variants of concern (VOCs) and sub-lineages that have recently surfaced in the post-pandemic years. We assess the effectiveness of existing vaccines, including their booster doses, against these emerging variants and subvariants, such as BA.2-derived sub-lineages, XBB sub-lineages, and BA.2.86 (Pirola). Furthermore, we discuss the latest advancements in vaccine technology, including multivalent and pan-coronavirus approaches, along with the development of several next-generation coronavirus vaccines, such as exosome-based, virus-like particle (VLP), mucosal, and nanomaterial-based vaccines. Finally, we highlight the key challenges and critical areas for future research to address the evolving threat of SARS-CoV-2 subvariants and to develop strategies for combating the emergence of new viral threats, thereby improving preparedness for future pandemics.

Nanomechanical characterization of soft nanomaterial using atomic force microscopy

Atomic force microscopy (AFM) is a promising method for generating high-spatial-resolution images, providing insightful perspectives on the nanomechanical attributes of soft matter, including cells, bacteria, viruses, proteins, and nanoparticles. AFM is widely used in biological and pharmaceutical sciences because it can scrutinize mechanical properties under physiological conditions. We comprehensively reviewed experimental techniques and fundamental mathematical models to investigate the mechanical properties, including elastic moduli and binding forces, of soft materials. To determine these mechanical properties, two-dimensional arrays of force-distance (f-d) curves are obtained through AFM indentation experiments using the force volume technique. For elasticity determination, models are divided into approach f-d curve-based models, represented by the Hertz model, and retract f-d curve-based models, exemplified by the Johnson-Kendall-Roberts and Derjaguin-Müller-Toporov models. Especially, the Chen, Tu, and Cappella models, developed from the Hertz model, are used for thin samples on hard substrates. Additionally, the establishment of physical or chemical bonds during indentation experiments, observable in retract f-d curves, is crucial for the adhesive properties of samples and binding affinity between antibodies (receptors) and antigens (ligands). Chemical force microscopy, single-molecule force spectroscopy, and single-cell force spectroscopy are primary AFM methods that provide a comprehensive view of such properties through retract curve analysis. Furthermore, this paper, structured into key thematic sections, also reviews the exemplary application of AFM across multiple scientific disciplines. Notably, cancer cells are softer than healthy cells, although more sophisticated investigations are required for prognostic applications. AFM also investigates how bacteria adapt to antibiotics, addressing antimicrobial resistance, and reveals that stiffer virus capsids indicate reduced infectivity, aiding in the development of new strategies to combat viral infections. Moreover, AFM paves the way for innovative therapeutic approaches in designing effective drug delivery systems by providing insights into the physical properties of soft nanoparticles and the binding affinity of target moieties. Our review provides researchers with representative studies applying AFM to a wide range of cross-disciplinary research.

Molecular Basis of High-Blood-Pressure-Enhanced and High-Fever-Temperature-Weakened Receptor-Binding Domain/Peptidase Domain Binding: A Molecular Dynamics Simulation Study

The entry and infection of the Severe Acute Respiratory Syndrome Coronavirus 2 virus (SARS-CoV-2) involve recognition and binding of the receptor-binding domain (RBD) of the virus surface spike protein to the peptidase domain (PD) of the host cellular Angiotensin-Converting Enzyme-2 (ACE2) receptor. ACE2 is also involved in normal blood pressure control. An association between hypertension and COVID-19 severity and fatality is evident, but how hypertension predisposes patients diagnosed with COVID-19 to unfavorable outcomes remains unclear. High temperature early during SARS-CoV-2 infection impairs binding to human cells and retards viral progression. Low body temperature can prelude poor prognosis. In this study, all-atom molecular dynamics simulations were performed to examine the effects of high pressure and temperature on RBD/PD binding. A high blood pressure of 940 mmHg enhanced RBD/PD binding. A high temperature above 315 K significantly weakened RBD/PD binding, while a low temperature of 305 K enhanced binding. The curvature of the PD α1-helix and proximity of the PD β3β4-hairpin tip to the RBM motif affected the compactness of the binding interface and, hence, binding affinity. These findings provide novel insights into the underlying mechanisms by which hypertension predisposes patients to unfavorable outcomes in COVID-19 and how an initial high temperature retards viral progression.

AFM reveals differential effects of acidification on LDL- and oxidized LDL-receptor interactions: biomechanical implications in atherogenesis

The receptor recognition and interaction of plasma lipoproteins (e.g., native low-density lipoproteins (LDL)/oxidized low-density lipoproteins (oxLDL), as well as the influence of microenvironmental/lysosomal acidification, play critical roles in lipoprotein metabolism and diseases (e.g., atherosclerosis) but have been less investigated. Here, the recognition/interaction of LDL or oxLDL with LDL receptor (LDLR) or CD36 (a scavenger receptor) or with living cells at various pHs was evaluated mainly via atomic force microscopy (AFM). To improve force measurement accuracy, a novel, micro-droplet-based method for AFM probe functionalization was developed. We found that solution acidification significantly reduced the LDL-LDLR binding at pH ≤ 6.4, whereas the oxLDL-CD36 binding had no significant change until pH ≤ 4.4. Compared with a traditional immersion method, our micro-droplet method for AFM probe functionalization produced more accurate interaction forces, and revealed that acidification significantly reduced the LDL-LDLR/cell interaction forces, instead of the oxLDL-CD36/cell-specific interaction forces and nonspecific interaction forces. The data imply that the LDL-LDLR/cell recognition and interaction are susceptible to acidification, whereas the oxLDL-CD36/cell recognition and interaction are tolerant of acidification. The results may provide important novel information and biomechanical/pathological implications for understanding lipoprotein metabolism and atherosclerosis.

Pilot study: a descriptive-retrospective analysis of SARS-CoV-2 variants distribution and phylogenesis in the Phlegraean area

COVID-19 disease, caused by SARS-CoV-2 virus, marked the pandemic era, opening the way to next-generation sequencing in the viral diagnostic field. SARS-CoV-2 viral genome sequencing makes it possible to identify mutations in the virus and to track the diffusion of these variants in specific geographic area and in time. Variant sequences help understand how the virus spreads and how it can be contained, as well as for developing more effective vaccines and therapies. Indeed, monitoring the evolution of a virus allows us to quickly detect the potential selection of a super mutation, which can make a virus even more contagious and dangerous in terms of human health consequences. In light of this, in our pilot study, we decided to profile the SARS-CoV-2 genome, recruiting 38 patients divided according to age, sex, vaccination status and symptoms, ascertaining their positivity to the virus. Specific strains of SARS-CoV-2 have been identified and effective through next-generation sequencing. This analysis made it possible to obtain information on the variants of the virus and their spread in the Campania region of the Phlegraean area, in the municipalities of Bacoli, Pozzuoli and Monte di Procida from December 2021 to February 2023 and on the effect of long-term measures COVID-19 in our sample. The advantage of using NGS in diagnosis is the introduction of tests on many genes in a relatively short time and at relatively low costs, with a consequent increase in a precise molecular diagnosis and helps to identify ad personam therapies.

A comprehensive review of current insights into the virulence factors of SARS-CoV-2

The evolution of SARS-CoV-2 pathogenicity has been a major focus of attention. However, the determinants of pathogenicity are still unclear. Various hypotheses have attempted to elucidate the mechanisms underlying the evolution of viral pathogenicity, but a definitive conclusion has yet to be reached. Here, we review the potential impact of all proteins in SARS-CoV-2 on the viral pathogenic process and analyze the effects of their mutations on pathogenicity evolution. We aim to summarize which virus-encoded proteins are crucial in influencing viral pathogenicity, defined as disease severity following infection. Mutations in these key proteins, which are the virulence factors in SARS-CoV-2, may be the driving forces behind the evolution of viral pathogenicity. Mutations in the S protein can impact viral entry and fusogenicity. Mutations in proteins such as NSP2, NSP5, NSP14, and ORF7a can alter the virus's ability to suppress host protein synthesis and innate immunity. Mutations in NSP3, NSP4, NSP6, N protein, NSP5, and NSP12 may alter viral replication efficiency. The combined effects of mutations in the S protein and NSP6 can significantly reduce viral replication. In addition, various viral proteins, including ORF3a, ORF8, NSP4, Spike protein, N protein, and E protein, directly participate in the inflammatory process. Mutations in these proteins can modulate the levels of inflammation following infection. Collectively, these viral protein mutations can influence SARS-CoV-2 pathogenicity by impacting viral immune evasion, replication capacity, and the level of inflammation mediated by infection. In conclusion, the evolution of SARS-CoV-2 pathogenicity is likely determined by multiple virulence factors.

Impact of African-Specific ACE2 Polymorphisms on Omicron BA.4/5 RBD Binding and Allosteric Communication Within the ACE2-RBD Protein Complex

Severe acute respiratory symptom coronavirus 2 (SARS-CoV-2) infection occurs via the attachment of the spike (S) protein's receptor binding domain (RBD) to human ACE2 (hACE2). Natural polymorphisms in hACE2, particularly at the interface, may alter RBD-hACE2 interactions, potentially affecting viral infectivity across populations. This study identified the effects of six naturally occurring hACE2 polymorphisms with high allele frequency in the African population (S19P, K26R, M82I, K341R, N546D and D597Q) on the interaction with the S protein RBD of the BA.4/5 Omicron sub-lineage through post-molecular dynamics (MD), inter-protein interaction and dynamic residue network (DRN) analyses. Inter-protein interaction analysis suggested that the K26R variation, with the highest interactions, aligns with reports of enhanced RBD binding and increased SARS-CoV-2 susceptibility. Conversely, S19P, showing the fewest interactions and largest inter-protein distances, agrees with studies indicating it hinders RBD binding. The hACE2 M82I substitution destabilized RBD-hACE2 interactions, reducing contact frequency from 92 (WT) to 27. The K341R hACE2 variant, located distally, had allosteric effects that increased RBD-hACE2 contacts compared to WThACE2. This polymorphism has been linked to enhanced affinity for Alpha, Beta and Delta lineages. DRN analyses revealed that hACE2 polymorphisms may alter the interaction networks, especially in key residues involved in enzyme activity and RBD binding. Notably, S19P may weaken hACE2-RBD interactions, while M82I showed reduced centrality of zinc and chloride-coordinating residues, hinting at impaired communication pathways. Overall, our findings show that hACE2 polymorphisms affect S BA.4/5 RBD stability and modulate spike RBD-hACE2 interactions, potentially influencing SARS-CoV-2 infectivity-key insights for vaccine and therapeutic development.

Inhibition potential of natural flavonoids against selected omicron (B.1.19) mutations in the spike receptor binding domain of SARS-CoV-2: a molecular modeling approach

The omicron (B.1.19) variant of contagious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is considered a variant of concern (VOC) due to its increased transmissibility and highly infectious nature. The spike receptor-binding domain (RBD) is a hotspot of mutations and is regarded as a prominent target for screening drug candidates owing to its crucial role in viral entry and immune evasion. To date, no effective therapy or antivirals have been reported; therefore, there is an urgent need for rapid screening of antivirals. An extensive molecular modelling study has been performed with the primary goal to assess the inhibition potential of natural flavonoids as inhibitors against RBD from a manually curated library. Out of 40 natural flavonoids, five natural flavonoids, namely tomentin A (-8.7 kcal/mol), tomentin C (-8.6 kcal/mol), hyperoside (-8.4 kcal/mol), catechin gallate (-8.3 kcal/mol), and corylifol A (-8.2 kcal/mol), have been considered as the top-ranked compounds based on their binding affinity and molecular interaction profiling. The state-of-the-art molecular dynamics (MD) simulations of these top-ranked compounds in complex with RBD exhibited stable dynamics and structural compactness patterns on 200 nanoseconds. Additionally, complexes of these molecules demonstrated favorable free binding energies and affirmed the docking and simulation results. Moreover, the post-simulation validation of these interacted flavonoids using principal component analysis (PCA) revealed stable interaction patterns with RBD. The integrated results suggest that tomentin A, tomentin C, hyperoside, catechin gallate, and corylifol A might be effective against the emerging variants of SARS-CoV-2 and should be further evaluated using in-vitro and in-vivo experiments.Communicated by Ramaswamy H. Sarma.

Dataset of SARS-CoV-2 spike protein receptor binding domain variants in complex with antigen-binding fragments targeting COVID-19 vaccine-referenced variants

In this paper, we present a dataset of homology-modeled structures of SARS-CoV-2 Spike protein Receptor Binding Domain (RBD) variants complexed with antigen-binding fragments (Fab) derived from the PDB structures 8GPY (Omicron BA.4/5 RBD in complex with a neutralizing antibody scFv), 8H7Z (BA.2 RBD in complex with BA7535 Fab), and 8XE9 (XBB.1.5 RBD in complex with BD55-1205). The dataset consists of six sets of complex structures generated by combining 14 RBD variants with three different Fab pairs. The SARS-CoV-2 Spike protein sequence variants included in the dataset are Wild Type, BETA, EPSILON, IOTA, ETA, GAMMA, LAMBDA, KAPPA, BA.2, BA.4, XBB.1.5, EG.5.1, and KP.2. Notably, the KP.2 variant, which has gained attention due to its inclusion in recent vaccine updates (https://www.ema.europa.eu/), is also part of this dataset. The models were refined using the Schrödinger Bioluminate suite of software. For each variant, the homology-modeled RBDs were complexed with the Fab fragments from 8GPY, 8H7Z, and 8XE9 by grafting them onto the RBDs, followed by energy minimization, both individually and in combination. This process resulted in a comprehensive dataset of RBD-Fab complexes, suitable for comparative analysis and further investigations. Binding affinities between the RBD-Fab pairs were calculated using the Prime MM-GBSA tool (VSGB solvation model and OPLS4 force field), enabling the ranking of antigen-antibody interactions. Structural minimizations were performed to accurately estimate interaction energies, providing insights into the efficacy of antibody binding across different variants. This dataset provides high-quality structural data that can be reused for in-depth studies of antibody-antigen interactions, particularly in the context of vaccine efficacy and viral immune evasion strategies. The inclusion of the KP.2 variant, which is central to the latest COVID-19 vaccine updates, makes these homology models especially relevant. Supplementary files include the homology-modeled structures, computed binding affinities, and quality assessments (QMEANDisCo) for each model, ensuring reproducibility and reliability for further analyses.

A computationally designed antigen eliciting broad humoral responses against SARS-CoV-2 and related sarbecoviruses

The threat of spillovers of coronaviruses associated with the severe acute respiratory syndrome (SARS) from animals to humans necessitates vaccines that offer broader protection from sarbecoviruses. By leveraging a viral-genome-informed computational method for selecting immune-optimized and structurally engineered antigens, here we show that a single antigen based on the receptor binding domain of the spike protein of sarbecoviruses elicits broad humoral responses against SARS-CoV-1, SARS-CoV-2, WIV16 and RaTG13 in mice, rabbits and guinea pigs. When administered as a DNA immunogen or by a vector based on a modified vaccinia virus Ankara, the optimized antigen induced vaccine protection from the Delta variant of SARS-CoV-2 in mice genetically engineered to express angiotensin-converting enzyme 2 and primed by a viral-vector vaccine (AZD1222) against SARS-CoV-2. A vaccine formulation incorporating mRNA coding for the optimized antigen further validated its broad immunogenicity. Vaccines that elicit broad immune responses across subgroups of coronaviruses may counteract the threat of zoonotic spillovers of betacoronaviruses.

Discovery of a heparan sulfate binding domain in monkeypox virus H3 as an anti-poxviral drug target combining AI and MD simulations

Viral adhesion to host cells is a critical step in infection for many viruses, including monkeypox virus (MPXV). In MPXV, the H3 protein mediates viral adhesion through its interaction with heparan sulfate (HS), yet the structural details of this interaction have remained elusive. Using AI-based structural prediction tools and molecular dynamics (MD) simulations, we identified a novel, positively charged α-helical domain in H3 that is essential for HS binding. This conserved domain, found across orthopoxviruses, was experimentally validated and shown to be critical for viral adhesion, making it an ideal target for antiviral drug development. Targeting this domain, we designed a protein inhibitor, which disrupted the H3-HS interaction, inhibited viral infection in vitro and viral replication in vivo, offering a promising antiviral candidate. Our findings reveal a novel therapeutic target of MPXV, demonstrating the potential of combination of AI-driven methods and MD simulations to accelerate antiviral drug discovery.

Structural Immunology of SARS-CoV-2

The SARS-CoV-2 spike (S) protein has undergone significant evolution, enhancing both receptor binding and immune evasion. In this review, we summarize ongoing efforts to develop antibodies targeting various epitopes of the S protein, focusing on their neutralization potency, breadth, and escape mechanisms. Antibodies targeting the receptor-binding site (RBS) typically exhibit high neutralizing potency but are frequently evaded by mutations in SARS-CoV-2 variants. In contrast, antibodies targeting conserved regions, such as the S2 stem helix and fusion peptide, exhibit broader reactivity but generally lower neutralization potency. However, several broadly neutralizing antibodies have demonstrated exceptional efficacy against emerging variants, including the latest omicron subvariants, underscoring the potential of targeting vulnerable sites such as RBS-A and RBS-D/CR3022. We also highlight public classes of antibodies targeting different sites on the S protein. The vulnerable sites targeted by public antibodies present opportunities for germline-targeting vaccine strategies. Overall, developing escape-resistant, potent antibodies and broadly effective vaccines remains crucial for combating future variants. This review emphasizes the importance of identifying key epitopes and utilizing antibody affinity maturation to inform future therapeutic and vaccine design.

Ongoing evolution of SARS-CoV-2 drives escape from mRNA vaccine-induced humoral immunity

With the onset of the COVID-19 pandemic 4 years ago, viral sequencing continues to document numerous individual mutations in the viral spike protein across many variants. To determine the ability of vaccine-mediated humoral immunity to combat continued SARS-CoV-2 evolution, we construct a comprehensive panel of pseudoviruses harboring each individual mutation spanning 4 years of the pandemic to understand the fitness cost and resistance benefits of each. These efforts identify numerous mutations that escape from vaccine-induced humoral immunity. Across 50 variants and 131 mutants we construct, we observe progressive loss of neutralization across variants, irrespective of vaccine doses, as well as increasing infectivity and ACE2 binding. Importantly, the recent XBB.1.5 booster significantly increases titers against most variants but not JN.1, KP.2, or KP.3. These findings demonstrate that variants continue to evade updated mRNA vaccines, highlighting the need for different approaches to control SARS-CoV-2 transmission.

Computational Analysis of the Accumulation of Mutations in Therapeutically Important RNA Viral Proteins During Pandemics with Special Emphasis on SARS-CoV-2

Single stranded RNA viruses are primary causative agents for pandemics, causing extensive morbidity and mortality worldwide. A pivotal question in pandemic preparedness and therapeutic intervention is what are the specific mutations which are more likely to emerge during such global health crises? This study aims to identify markers for mutations with the highest probability of emergence in these pandemics, focusing on the SARS-CoV-2 spike protein, an essential and therapeutically significant viral protein, starting from sequence information from the onset of the pandemic until July 2022. Quite consistently, we observed that emerged mutations tended to demonstrate a high genetic score, which reflects high similarity of the type of codon required for translation between an amino acid and to the mutated one. Further, this pattern is also observed in therapeutically significant proteins of other ssRNA pandemic viruses, including influenza (HA, NA), spike proteins of Ebola, envelope of Dengue and Chikungunya. We propose that the genetic score serves as an initial indicator, preceding the actual impact of the mutation on viral fitness. Finally, we developed a comprehensive computational pipeline to further explore and predict the subsequent effects of mutations on viral fitness. We believe that our pipeline can narrow down and predict future mutations in therapeutically important viral proteins during a pandemic.

Emergence and fixation of SARS-CoV-2 minority variants in a chronically infected patient receiving therapy in Denmark

SARS-CoV-2 variants of concern (VOC), such as Delta and Omicron have harbored mutations, which increased viral infectivity or ability to evade neutralizing antibodies. Immunocompromised patients might be a source of some of these emerging variants. In this study, we sequenced 17 consecutive samples from an immunocompromised patient with a long-term SARS-CoV-2 infection with the pre-VOC era lineage B.1.177.35. We here describe the emergence of 73 nonsynonymous minority variants in this patient and show that 10 of these mutations became dominant in the viral population during the treatment period. Four of these were seen throughout the infection period and had a very low global prevalence, although three of them were also observed later in the Alpha, Delta, and Omicron lineages. We also found that two adjacent nsp12 variants (M785I and S786P) belonged to different quasi-species and competed during the early stages of infection and remdesivir administration. This emphasizes the importance of ongoing genome surveillance of SARS-CoV-2 among immunocpromised patients.

AlphaFold2 Modeling and Molecular Dynamics Simulations of the Conformational Ensembles for the SARS-CoV-2 Spike Omicron JN.1, KP.2 and KP.3 Variants: Mutational Profiling of Binding Energetics Reveals Epistatic Drivers of the ACE2 Affinity and Escape Hotspots of Antibody Resistance

The most recent wave of SARS-CoV-2 Omicron variants descending from BA.2 and BA.2.86 exhibited improved viral growth and fitness due to convergent evolution of functional hotspots. These hotspots operate in tandem to optimize both receptor binding for effective infection and immune evasion efficiency, thereby maintaining overall viral fitness. The lack of molecular details on structure, dynamics and binding energetics of the latest FLiRT and FLuQE variants with the ACE2 receptor and antibodies provides a considerable challenge that is explored in this study. We combined AlphaFold2-based atomistic predictions of structures and conformational ensembles of the SARS-CoV-2 spike complexes with the host receptor ACE2 for the most dominant Omicron variants JN.1, KP.1, KP.2 and KP.3 to examine the mechanisms underlying the role of convergent evolution hotspots in balancing ACE2 binding and antibody evasion. Using the ensemble-based mutational scanning of the spike protein residues and computations of binding affinities, we identified binding energy hotspots and characterized the molecular basis underlying epistatic couplings between convergent mutational hotspots. The results suggested the existence of epistatic interactions between convergent mutational sites at L455, F456, Q493 positions that protect and restore ACE2-binding affinity while conferring beneficial immune escape. To examine immune escape mechanisms, we performed structure-based mutational profiling of the spike protein binding with several classes of antibodies that displayed impaired neutralization against BA.2.86, JN.1, KP.2 and KP.3. The results confirmed the experimental data that JN.1, KP.2 and KP.3 harboring the L455S and F456L mutations can significantly impair the neutralizing activity of class 1 monoclonal antibodies, while the epistatic effects mediated by F456L can facilitate the subsequent convergence of Q493E changes to rescue ACE2 binding. Structural and energetic analysis provided a rationale to the experimental results showing that BD55-5840 and BD55-5514 antibodies that bind to different binding epitopes can retain neutralizing efficacy against all examined variants BA.2.86, JN.1, KP.2 and KP.3. The results support the notion that evolution of Omicron variants may favor emergence of lineages with beneficial combinations of mutations involving mediators of epistatic couplings that control balance of high ACE2 affinity and immune evasion.

CD4+ and CD8+ T cells are required to prevent SARS-CoV-2 persistence in the nasal compartment

SARS-CoV-2 infection induces the generation of virus-specific CD4+ and CD8+ effector and memory T cells. However, the contribution of T cells in controlling SARS-CoV-2 during infection is not well understood. Following infection of C57BL/6 mice, SARS-CoV-2-specific CD4+ and CD8+ T cells are recruited to the respiratory tract, and a vast proportion secrete the cytotoxic molecule granzyme B. Using depleting antibodies, we found that T cells within the lungs play a minimal role in viral control, and viral clearance occurs in the absence of both CD4+ and CD8+ T cells through 28 days postinfection. In the nasal compartment, depletion of both CD4+ and CD8+ T cells, but not individually, results in persistent, culturable virus replicating in the nasal epithelial layer through 28 days postinfection. Viral sequencing analysis revealed adapted mutations across the SARS-CoV-2 genome, including a large deletion in ORF6. Overall, our findings highlight the importance of T cells in controlling virus replication within the respiratory tract during SARS-CoV-2 infection.

A positive selection at binding site 501 in the B.1 lineage might have triggered the highly infectious sub-lineages of SARS-CoV-2

The descendants of the B lineage are the most predominant variants among the SARS-CoV-2 virus due to the incorporation of new mutations augmenting the infectivity of the virus. There is a substantial increase in the transition transversion bias, nucleotide diversity and purifying selection on the spike protein in the descendants of the B lineage of the SARS-CoV-2 virus on a temporal scale. A strong bias for C-to-U substitutions is found in the genes encoding spike protein in this lineage. The positive selection has operated on the spike gene of B lineages and its sub-lineages. The B.1 lineage has undergone positive selection on site 501 of the receptor binding domain ultimately reflected in a key substitution N501Y in its three descendant lineages namely B.1.1.7, B.1.351 and P.1. The intensity of purifying selection on the multiple sites of the spike gene has increased substantially in the sub-lineages of B.1 in a timescale. The binding site 501 on the spike protein in B lineage is found to coevolve with other amino acid sites. This study sheds light on the evolutionary trajectory of the B lineage into highly infectious descendants in the recent past under the influence of positive and purifying selection exerted by natural immunity and vaccination of the host.

Mutations in the Receptor Binding Domain of Severe Acute Respiratory Coronavirus-2 Omicron Variant Spike Protein Significantly Stabilizes Its Conformation

The Omicron variant and its sub-lineages are the only current circulating SARS-CoV-2 viruses worldwide. In this study, the conformational stability of the isolated Receptor Binding Domain (RBD) of Omicron's spike protein is examined in detail. The parent Omicron lineage has over ten mutations in the ACE2 binding region of the RBD that are specifically associated with its β hairpin loop domain. It is demonstrated through biophysical molecular computations that the mutations in the β hairpin loop domain significantly increase the intra-protein interaction energies of intra-loop and loop-RBD interactions. The interaction energy increases include the formation of new hydrogen bonds in the β hairpin loop domain that help stabilize this critical ACE2 binding region. Our results also agree with recent experiments on the stability of Omicron's core β barrel domain, outside of its loop domain, and help demonstrate the overall conformational stability of the Omicron RBD. It is further shown here through dynamic simulations that the unbound state of the Omicron RBD remains closely aligned with the bound state configuration, which was not observed for the wild-type RBD. Overall, these studies demonstrate the significantly increased conformational stability of Omicron over its wild-type configuration and raise a number of questions on whether conformational stability could be a positive selection feature of SARS-CoV-2 viral mutational changes.

Identifications of novel host cell factors that interact with the receptor-binding domain of the SARS-CoV-2 spike protein

SARS-CoV-2 entry into host cells is facilitated by the interaction between the receptor-binding domain of its spike protein (CoV2-RBD) and host cell receptor, ACE2, promoting viral membrane fusion. The virus also uses endocytic pathways for entry, but the mediating host factors remain largely unknown. It is also unknown whether mutations in the RBD of SARS-CoV-2 variants promote interactions with additional host factors to promote viral entry. Here, we used the GST pull-down approach to identify novel surface-located host factors that bind to CoV2-RBD. One of these factors, SH3BP4, regulates internalization of CoV2-RBD in an ACE2-independent but integrin- and clathrin-dependent manner and mediates SARS-CoV-2 pseudovirus entry, suggesting that SH3BP4 promotes viral entry via the endocytic route. Many of the identified factors, including SH3BP4, ADAM9, and TMEM2, show stronger affinity to CoV2-RBD than to RBD of the less infective SARS-CoV, suggesting SARS-CoV-2-specific utilization. We also found factors preferentially binding to the RBD of the SARS-CoV-2 Delta variant, potentially enhancing its entry. These data identify the repertoire of host cell surface factors that function in the events leading to the entry of SARS-CoV-2.

Mutational dynamics of SARS-CoV-2: Impact on future COVID-19 vaccine strategies

The rapid emergence of multiple strains of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) has sparked profound concerns regarding the ongoing evolution of the virus and its potential impact on global health. Classified by the World Health Organization (WHO) as variants of concern (VOC), these strains exhibit heightened transmissibility and pathogenicity, posing significant challenges to existing vaccine strategies. Despite widespread vaccination efforts, the continual evolution of SARS-CoV-2 variants presents a formidable obstacle to achieving herd immunity. Of particular concern is the coronavirus spike (S) protein, a pivotal viral surface protein crucial for host cell entry and infectivity. Mutations within the S protein have been shown to enhance transmissibility and confer resistance to antibody-mediated neutralization, undermining the efficacy of traditional vaccine platforms. Moreover, the S protein undergoes rapid molecular evolution under selective immune pressure, leading to the emergence of diverse variants with distinct mutation profiles. This review underscores the urgent need for vigilance and adaptation in vaccine development efforts to combat the evolving landscape of SARS-CoV-2 mutations and ensure the long-term effectiveness of global immunization campaigns.

Molecular Mechanism of Interaction between DNA Aptamer and Receptor-Binding Domain of Severe Acute Respiratory Syndrome Coronavirus 2 Variants Revealed by Steered Molecular Dynamics Simulations

The ongoing SARS-CoV-2 pandemic has underscored the urgent need for versatile and rapidly deployable antiviral strategies. While vaccines have been pivotal in controlling the spread of the virus, the emergence of new variants continues to pose significant challenges to global health. Here, our study focuses on a novel approach to antiviral therapy using DNA aptamers, short oligonucleotides with high specificity and affinity for their targets, as potential inhibitors against the spike protein of SARS-CoV-2 variants Omicron and JN.1. Our research utilizes steered molecular dynamics (SMD) simulations to elucidate the binding mechanisms of a specifically designed DNA aptamer, AM032-4, to the receptor-binding domain (RBD) of the aforementioned variants. The simulations reveal detailed molecular insights into the aptamer-RBD interaction, demonstrating the aptamer's potential to maintain effective binding in the face of rapid viral evolution. Our work not only demonstrates the dynamic interaction between aptamer-RBD for possible antiviral therapy but also introduces a computational method to study aptamer-protein interactions.

An Omicron-specific, self-amplifying mRNA booster vaccine for COVID-19: a phase 2/3 randomized trial

Here we conducted a multicenter open-label, randomized phase 2 and 3 study to assess the safety and immunogenicity of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron-specific (BA.1/B.1.1.529), monovalent, thermostable, self-amplifying mRNA vaccine, GEMCOVAC-OM, when administered intradermally as a booster in healthy adults who had received two doses of BBV152 or ChAdOx1 nCoV-19. GEMCOVAC-OM was well tolerated with no related serious adverse events in both phase 2 and phase 3. In phase 2, the safety and immunogenicity of GEMCOVAC-OM was compared with our prototype mRNA vaccine GEMCOVAC-19 (D614G variant-specific) in 140 participants. At day 29 after vaccination, there was a significant rise in anti-spike (BA.1) IgG antibodies with GEMCOVAC-OM (P < 0.0001) and GEMCOVAC-19 (P < 0.0001). However, the IgG titers (primary endpoint) and seroconversion were higher with GEMCOVAC-OM (P < 0.0001). In phase 3, GEMCOVAC-OM was compared with ChAdOx1 nCoV-19 in 3,140 participants (safety cohort), which included an immunogenicity cohort of 420 participants. At day 29, neutralizing antibody titers against the BA.1 variant of SARS-CoV-2 were significantly higher than baseline in the GEMCOVAC-OM arm (P < 0.0001), but not in the ChAdOx1 nCoV-19 arm (P = 0.1490). GEMCOVAC-OM was noninferior (primary endpoint) and superior to ChAdOx1 nCoV-19 in terms of neutralizing antibody titers and seroconversion rate (lower bound 95% confidence interval of least square geometric mean ratio >1 and difference in seroconversion >0% for superiority). At day 29, anti-spike IgG antibodies and seroconversion (secondary endpoints) were significantly higher with GEMCOVAC-OM (P < 0.0001). These results demonstrate that GEMCOVAC-OM is safe and boosts immune responses against the B.1.1.529 variant. Clinical Trial Registry India identifier: CTRI/2022/10/046475 .

Innovations and Challenges in the Development of COVID-19 Vaccines for a Safer Tomorrow

Vaccination, a historically effective public health intervention, has shielded millions from various diseases. Lessons from severe acute respiratory syndrome coronavirus (SARS-CoV) have improved COVID-19 vaccine development. Despite mRNA vaccines' efficacy, emerging variants pose challenges, exhibiting increased transmissibility, infectivity, and severity. Developing COVID-19 vaccines has faced hurdles due to urgency, limited virus understanding, and the need for safe solutions. Genetic variability necessitates continuous vaccine adjustments and production challenges demand scaling up manufacturing with stringent quality control. This review explores SARS-CoV-2's evolution, upcoming mutations that challenge vaccines, and strategies such as structure-based, T cell-based, respiratory mucosal-based, and nanotechnology approaches for vaccine development. This review insight provides a roadmap for navigating virus evolution and improving vaccine development.

Molecular force-induced liberation of transforming growth factor-beta remodels the spleen for ectopic liver regeneration

BACKGROUND & AIMS

Ectopic liver regeneration in the spleen is a promising alternative to organ transplantation for treating liver failure. To accommodate transplanted liver cells, the splenic tissue must undergo structural changes to increase extracellular matrix content, demanding a safe and efficient approach for tissue remodelling.

METHODS

We synthesised sulphated hyaluronic acid (sHA) with an affinity for the latent complex of transforming growth factor-β (TGF-β) and cross-linked it into a gel network (sHA-X) via click chemistry. We injected this glycan into the spleens of mice to induce splenic tissue remodelling via supraphysiological activation of endogenous TGF-β.

RESULTS

sHA-X efficiently bound to the abundant latent TGF-β in the spleen. It provided the molecular force to liberate the active TGF-β dimers from their latent complex, mimicking the 'bind-and-pull' mechanism required for physiological activation of TGF-β and reshaping the splenic tissue to support liver cell growth. Hepatocytes transplanted into the remodelled spleen developed into liver tissue with sufficient volume to rescue animals with a metabolic liver disorder (Fah-/- transgenic model) or following 90% hepatectomy, with no adverse effects observed and no additional drugs required.

CONCLUSION

Our findings highlight the efficacy and translational potential of using sHA-X to remodel a specific organ by mechanically activating one single cytokine, representing a novel strategy for the design of biomaterials-based therapies for organ regeneration.

IMPACT AND IMPLICATIONS

Cell transplantation may provide a lifeline to millions of patients with end-stage liver diseases, but their severely damaged livers being unable to accommodate the transplanted cells is a crucial hurdle. Herein, we report an approach to restore liver functions in another organ - the spleen - by activating one single growth factor in situ. This approach, based on a chemically designed polysaccharide that can mechanically liberate the active transforming growth factor-β to an unusually high level, promotes the function of abundant allogenic liver cells in the spleen, rescuing animals from lethal models of liver diseases and showing a high potential for clinical translation.

Characterization of a neutralizing antibody that recognizes a loop region adjacent to the receptor-binding interface of the SARS-CoV-2 spike receptor-binding domain

Although the global crisis caused by the coronavirus disease 2019 (COVID-19) pandemic is over, the global epidemic of the disease continues. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the cause of COVID-19, initiates infection via the binding of the receptor-binding domain (RBD) of its spike protein to the human angiotensin-converting enzyme II (ACE2) receptor, and this interaction has been the primary target for the development of COVID-19 therapeutics. Here, we identified neutralizing antibodies against SARS-CoV-2 by screening mouse monoclonal antibodies and characterized an antibody, CSW1-1805, that targets a narrow region at the RBD ridge of the spike protein. CSW1-1805 neutralized several variants in vitro and completely protected mice from SARS-CoV-2 infection. Cryo-EM and biochemical analyses revealed that this antibody recognizes the loop region adjacent to the ACE2-binding interface with the RBD in both a receptor-inaccessible "down" state and a receptor-accessible "up" state and could stabilize the RBD conformation in the up-state. CSW1-1805 also showed different binding orientations and complementarity determining region properties compared to other RBD ridge-targeting antibodies with similar binding epitopes. It is important to continuously characterize neutralizing antibodies to address new variants that continue to emerge. Our characterization of this antibody that recognizes the RBD ridge of the spike protein will aid in the development of future neutralizing antibodies.IMPORTANCESARS-CoV-2 cell entry is initiated by the interaction of the viral spike protein with the host cell receptor. Therefore, mechanistic findings regarding receptor recognition by the spike protein help uncover the molecular mechanism of SARS-CoV-2 infection and guide neutralizing antibody development. Here, we characterized a SARS-CoV-2 neutralizing antibody that recognizes an epitope, a loop region adjacent to the receptor-binding interface, that may be involved in the conformational transition of the receptor-binding domain (RBD) of the spike protein from a receptor-inaccessible "down" state into a receptor-accessible "up" state, and also stabilizes the RBD in the up-state. Our mechanistic findings provide new insights into SARS-CoV-2 receptor recognition and guidance for neutralizing antibody development.

COVID-19: From emerging variants to vaccination

The vigorous spread of SARS-CoV-2 resulted in the rapid infection of millions of people worldwide and devastation of not only public healthcare, but also social, educational, and economic infrastructures. The evolution of SARS-CoV-2 over time is due to the mutations that occurred in the genome during each replication. These mutated forms of SARS-CoV-2, otherwise known as variants, were categorized as variants of interest (VOI) or variants of concern (VOC) based on the increased risk of transmissibility, disease severity, immune escape, decreased effectiveness of current social measures, and available vaccines and therapeutics. The swift development of COVID-19 vaccines has been a great success for biomedical research, and billions of vaccine doses, including boosters, have been administered worldwide. BNT162b2 vaccine (Pfizer-BioNTech), mRNA-1273 (Moderna), ChAdOx1 nCoV-19 (AstraZeneca), and Janssen (Johnson & Johnson) are the four major COVID-19 vaccines that received early regulatory authorization based on their efficacy. However, some SARS-CoV-2 variants resulted in higher resistance to available vaccines or treatments. It has been four years since the first reported infection of SARS-CoV-2, yet the Omicron variant and its subvariants are still infecting people worldwide. Despite this, COVID-19 vaccines are still expected to be effective at preventing severe disease, hospitalization, and death from COVID. In this review, we provide a comprehensive overview of the COVID-19 pandemic focused on evolution of VOC and vaccination strategies against them.

Therapeutic development targeting host heparan sulfate proteoglycan in SARS-CoV-2 infection

The global pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an urgent need for effective therapeutic options. SARS-CoV-2 is a novel coronavirus responsible for the COVID-19 pandemic that has resulted in significant morbidity and mortality worldwide. The virus is known to enter host cells by binding to the angiotensin-converting enzyme 2 (ACE2) receptor, and emerging evidence suggests that heparan sulfate proteoglycans (HSPGs) play a crucial role in facilitating this process. HSPGs are abundant cell surface proteoglycan present in many tissues, including the lung, and have been shown to interact directly with the spike protein of SARS-CoV-2. This review aims to summarize the current understanding of the role of HSPGs in SARS-CoV-2 infection and the potential of developing new therapies targeting HSPGs.

Soluble ACE2 correlates with severe COVID-19 and can impair antibody responses

Identifying immune modulators that impact neutralizing antibody responses against severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is of great relevance. We postulated that high serum concentrations of soluble angiotensin-converting enzyme 2 (sACE2) might mask the spike and interfere with antibody maturation toward the SARS-CoV-2-receptor-binding motif (RBM). We tested 717 longitudinal samples from 295 COVID-19 patients and showed a 2- to 10-fold increase of enzymatically active sACE2 (a-sACE2), with up to 1 μg/mL total sACE2 in moderate and severe patients. Fifty percent of COVID-19 sera inhibited ACE2 activity, in contrast to 1.3% of healthy donors and 4% of non-COVID-19 pneumonia patients. A mild inverse correlation of a-sACE2 with RBM-directed serum antibodies was observed. In silico, we show that sACE2 concentrations measured in COVID-19 sera can disrupt germinal center formation and inhibit timely production of high-affinity antibodies. We suggest that sACE2 is a biomarker for COVID-19 and that soluble receptors may contribute to immune suppression informing vaccine design.

Single-molecule force stability of the SARS-CoV-2-ACE2 interface in variants-of-concern

Mutations in SARS-CoV-2 have shown effective evasion of population immunity and increased affinity to the cellular receptor angiotensin-converting enzyme 2 (ACE2). However, in the dynamic environment of the respiratory tract, forces act on the binding partners, which raises the question of whether not only affinity but also force stability of the SARS-CoV-2-ACE2 interaction might be a selection factor for mutations. Using magnetic tweezers, we investigate the impact of amino acid substitutions in variants of concern (Alpha, Beta, Gamma and Delta) and on force-stability and bond kinetic of the receptor-binding domain-ACE2 interface at a single-molecule resolution. We find a higher affinity for all of the variants of concern (>fivefold) compared with the wild type. In contrast, Alpha is the only variant of concern that shows higher force stability (by 17%) compared with the wild type. Using molecular dynamics simulations, we rationalize the mechanistic molecular origins of this increase in force stability. Our study emphasizes the diversity of contributions to the transmissibility of variants and establishes force stability as one of the several factors for fitness. Understanding fitness advantages opens the possibility for the prediction of probable mutations, allowing a rapid adjustment of therapeutics, vaccines and intervention measures.

Molecular insights into the adaptive evolution of SARS-CoV-2 spike protein

The COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has substantially damaged the global economy and human health. The spike (S) protein of coronaviruses plays a pivotal role in viral entry by binding to host cell receptors. Additionally, it acts as the primary target for neutralizing antibodies in those infected and is the central focus for currently utilized or researched vaccines. During the virus's adaptation to the human host, the S protein of SARS-CoV-2 has undergone significant evolution. As the COVID-19 pandemic has unfolded, new mutations have arisen and vanished, giving rise to distinctive amino acid profiles within variant of concern strains of SARS-CoV-2. Notably, many of these changes in the S protein have been positively selected, leading to substantial alterations in viral characteristics, such as heightened transmissibility and immune evasion capabilities. This review aims to provide an overview of our current understanding of the structural implications associated with key amino acid changes in the S protein of SARS-CoV-2. These research findings shed light on the intricate and dynamic nature of viral evolution, underscoring the importance of continuous monitoring and analysis of viral genomes. Through these molecular-level investigations, we can attain deeper insights into the virus's adaptive evolution, offering valuable guidance for designing vaccines and developing antiviral drugs to combat the ever-evolving viral threats.

Mechanistic insights into the C-type lectin receptor CLEC12A-mediated immune recognition of monosodium urate crystal

CLEC12A, a member of the C-type lectin receptor family involved in immune homeostasis, recognizes MSU crystals released from dying cells. However, the molecular mechanism underlying the CLEC12A-mediated recognition of MSU crystals remains unclear. Herein, we reported the crystal structure of the human CLEC12A-C-type lectin-like domain (CTLD) and identified a unique "basic patch" site on CLEC12A-CTLD that is necessary for the binding of MSU crystals. Meanwhile, we determined the interaction strength between CLEC12A-CTLD and MSU crystals using single-molecule force spectroscopy. Furthermore, we found that CLEC12A clusters at the cell membrane and seems to serve as an internalizing receptor of MSU crystals. Altogether, these findings provide mechanistic insights for understanding the molecular mechanisms underlying the interplay between CLEC12A and MSU crystals.

Pathophysiological, immunological, and inflammatory features of long COVID

The COVID-19 pandemic continues to cause severe global disruption, resulting in significant excess mortality, overwhelming healthcare systems, and imposing substantial social and economic burdens on nations. While most of the attention and therapeutic efforts have concentrated on the acute phase of the disease, a notable proportion of survivors experience persistent symptoms post-infection clearance. This diverse set of symptoms, loosely categorized as long COVID, presents a potential additional public health crisis. It is estimated that 1 in 5 COVID-19 survivors exhibit clinical manifestations consistent with long COVID. Despite this prevalence, the mechanisms and pathophysiology of long COVID remain poorly understood. Alarmingly, evidence suggests that a significant proportion of cases within this clinical condition develop debilitating or disabling symptoms. Hence, urgent priority should be given to further studies on this condition to equip global public health systems for its management. This review provides an overview of available information on this emerging clinical condition, focusing on the affected individuals' epidemiology, pathophysiological mechanisms, and immunological and inflammatory profiles.

A single-dose MCMV-based vaccine elicits long-lasting immune protection in mice against distinct SARS-CoV-2 variants

Current vaccines against COVID-19 elicit immune responses that are overall strong but wane rapidly. As a consequence, the necessary booster shots have led to vaccine fatigue. Hence, vaccines that would provide lasting protection against COVID-19 are needed, but are still unavailable. Cytomegaloviruses (CMV) elicit lasting and uniquely strong immune responses. Used as vaccine vectors, they may be attractive tools that obviate the need for boosters. Therefore, we tested the murine CMV (MCMV) as a vaccine vector against COVID-19 in relevant preclinical models of immunization and challenge. We have previously developed a recombinant murine CMV (MCMV) vaccine vector expressing the spike protein of the ancestral SARS-CoV-2 (MCMVS). In this study, we show that the MCMVS elicits a robust and lasting protection in young and aged mice. Notably, S-specific humoral and cellular immunity was not only maintained but even increased over a period of at least 6 months. During that time, antibody avidity continuously increased and expanded in breadth, resulting in neutralization of genetically distant variants, like Omicron BA.1. A single dose of MCMVS conferred rapid virus clearance upon challenge. Moreover, MCMVS vaccination controlled two immune-evading variants of concern (VoCs), the Beta (B.1.135) and the Omicron (BA.1) variants. Thus, CMV vectors provide unique advantages over other vaccine technologies, eliciting broadly reactive and long-lasting immune responses against COVID-19.

Deciphering the free energy landscapes of SARS-CoV-2 wild type and Omicron variant interacting with human ACE2

The binding of the receptor binding domain (RBD) of the SARS-CoV-2 spike protein to the host cell receptor angiotensin-converting enzyme 2 (ACE2) is the first step in human viral infection. Therefore, understanding the mechanism of interaction between RBD and ACE2 at the molecular level is critical for the prevention of COVID-19, as more variants of concern, such as Omicron, appear. Recently, atomic force microscopy has been applied to characterize the free energy landscape of the RBD-ACE2 complex, including estimation of the distance between the transition state and the bound state, xu. Here, using a coarse-grained model and replica-exchange umbrella sampling, we studied the free energy landscape of both the wild type and Omicron subvariants BA.1 and XBB.1.5 interacting with ACE2. In agreement with experiment, we find that the wild type and Omicron subvariants have similar xu values, but Omicron binds ACE2 more strongly than the wild type, having a lower dissociation constant KD.

Causes and Consequences of Coronavirus Spike Protein Variability

Coronaviruses are a large family of enveloped RNA viruses found in numerous animal species. They are well known for their ability to cross species barriers and have been transmitted from bats or intermediate hosts to humans on several occasions. Four of the seven human coronaviruses (hCoVs) are responsible for approximately 20% of common colds (hCoV-229E, -NL63, -OC43, -HKU1). Two others (SARS-CoV-1 and MERS-CoV) cause severe and frequently lethal respiratory syndromes but have only spread to very limited extents in the human population. In contrast the most recent human hCoV, SARS-CoV-2, while exhibiting intermediate pathogenicity, has a profound impact on public health due to its enormous spread. In this review, we discuss which initial features of the SARS-CoV-2 Spike protein and subsequent adaptations to the new human host may have helped this pathogen to cause the COVID-19 pandemic. Our focus is on host forces driving changes in the Spike protein and their consequences for virus infectivity, pathogenicity, immune evasion and resistance to preventive or therapeutic agents. In addition, we briefly address the significance and perspectives of broad-spectrum therapeutics and vaccines.

Molecular interactions between perlecan LG3 and the SARS-CoV-2 spike protein receptor binding domain

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a global health crisis with significant clinical morbidity and mortality. While angiotensin-converting enzyme 2 (ACE2) is the primary receptor for viral entry, other cell surface and extracellular matrix proteins may also bind to the viral receptor binding domain (RBD) within the SARS-CoV-2 spike protein. Recent studies have implicated heparan sulfate proteoglycans, specifically perlecan LG3, in facilitating SARS-CoV-2 binding to ACE2. However, the role of perlecan LG3 in SARS-CoV-2 pathophysiology is not well understood. In this study, we investigated the binding interactions between the SARS-CoV-2 spike protein RBD and perlecan LG3 through molecular modeling simulations and surface plasmon resonance (SPR) experiments. Our results indicate stable binding between LG3 and SARS-CoV-2 spike protein RBD, which may potentially enhance RBD-ACE2 interactions. These findings shed light on the role of perlecan LG3 in SARS-CoV-2 infection and provide insight into SARS-CoV-2 pathophysiology and potential therapeutic strategy for COVID-19.

Risk assessment of SARS-CoV-2 replicating and evolving in animals

The retransmissions of SARS-CoV-2 from several mammals - primarily mink and white-tailed deer - to humans have raised concerns for the emergence of a new animal-derived SARS-CoV-2 variant to worsen the pandemic. Here, we discuss animal species that are susceptible to natural or experimental infection with SARS-CoV-2 and can transmit the virus to mates or humans. We describe cutting-edge techniques to assess the impact of a mutation in the viral spike (S) protein on its receptor and on antibody binding. Our review of spike sequences of animal-derived viruses identified nine unique amino acid exchanges in the receptor-binding domain (RBD) that are not present in any variant of concern (VOC). These mutations are present in SARS-CoV-2 found in companion animals such as dogs and cats, and they exhibit a higher frequency in SARS-CoV-2 found in mink and white-tailed deer, suggesting that sustained transmissions may contribute to maintaining novel mutations. Four of these exchanges, such as Leu452Met, could undermine acquired immune protection in humans while maintaining high affinity for the human angiotensin-converting enzyme 2 (ACE2) receptor. Finally, we discuss important avenues of future research into animal-derived viruses with public health risks.

A Modified Recombinant DNA-Based SARS-CoV-2 Vaccine Expressing Stabilized Uncleavable Spike Protein Elicits Humoral and Cellular Immunity against Various SARS-CoV-2 Variants of Concern

The appearance of several variants of concern (VOCs) of SARS-CoV-2 affects the efficacy of currently available vaccines and causes continuous spread and reinfection between humans. These variants possess different spike (S) protein mutations, which could affect viral pathogenicity, transmission, and immune escape. Herein, we develop a synthetic codon-optimized DNA vaccine (VIU-1007) expressing full-length S protein. The developed vaccine is stabilized by two K986P and V987P proline substitutions and resistant to cleavage by proteases such as furin by deletion of arginine residues (R682, R683, and R685) in multibasic furin cleavage site (RRAR). Additionally, it carries K417N, E484K, N501Y, and D614G substitutions in the receptor binding domain (RBD) derived from the beta VOC. Following the validation and characterization of the in vitro S protein expression, the humoral and cellular immunogenicity of VIU-1007 was assessed in immunized Balb/c mice. While both regimens elicited a Th-1-biased immune response based on S1-specific binding IgG isotypes, three vaccine doses significantly enhanced IgG levels. Furthermore, CD4+ and CD8+ memory T cell responses in spleens and draining inguinal lymph nodes were significantly higher in mice received three doses of VIU-1007 when compared to those received two doses only. Importantly, sera from mice immunized with three doses showed broad neutralization breadth against several SARS-CoV-2 variants, including alpha, beta, gamma, delta, and omicron VOCs. Moreover, the sera showed limited neutralization capacity against SARS-CoV-1, Bat SARS-like coronavirus WIV1, and MERS-CoV. Together, while these data suggest the presence of common neutralizing-rich epitopes between SARS-CoV-2 variants and some other betacoronaviruses, the ongoing evolution of SARS-CoV-2 could result in escape from vaccine-induced immunity, which requires a continuous update of vaccines.

Genetic diversity and evolutionary patterns of SARS-CoV-2 among the Bhutanese population during the pandemic

BACKGROUND

The coronavirus disease 2019 (COVID-19) pandemic, caused by a dynamic virus, has had a profound global impact. Despite declining global COVID-19 cases and mortality rates, the emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants remains a major concern. This study provides a comprehensive analysis of the genomic sequences of SARS-CoV-2 within the Bhutanese population during the pandemic. The primary aim was to elucidate the molecular epidemiology and evolutionary patterns of SARS-CoV-2 in Bhutan, with a particular focus on genetic variations and lineage dynamics.

METHODS

Whole-genome sequences of SARS-CoV-2 collected from Bhutan between May 2020 and February 2023 (n=135) were retrieved from the Global Initiative on Sharing All Influenza Database.

RESULTS

The SARS-CoV-2 variants in Bhutan were predominantly classified within the Nextstrain clade 20A (31.1%), followed by clade 21L (20%) and clade 22D (15.6%). We identified 26 Pangolin lineages with variations in their spatial and temporal distribution. Bayesian time-scaled phylogenetic analysis estimated the time to the most recent common ancestor as February 15, 2020, with a substitution rate of 0.97×10-3 substitutions per site per year. Notably, the spike glycoprotein displayed the highest mutation frequency among major viral proteins, with 116 distinct mutations, including D614G. The Bhutanese isolates also featured mutations such as E484K, K417N, and S477N in the spike protein, which have implications for altered viral properties.

CONCLUSION

This is the first study to describe the genetic diversity of SARS-CoV-2 circulating in Bhutan during the pandemic, and this data can inform public health policies and strategies for preventing future outbreaks in Bhutan.

Predicting virus Fitness: Towards a structure-based computational model

Predicting the impact of new emerging virus mutations is of major interest in surveillance and for understanding the evolutionary forces of the pathogens. The SARS-CoV-2 surface spike-protein (S-protein) binds to human ACE2 receptors as a critical step in host cell infection. At the same time, S-protein binding to human antibodies neutralizes the virus and prevents interaction with ACE2. Here we combine these two binding properties in a simple virus fitness model, using structure-based computation of all possible mutation effects averaged over 10 ACE2 complexes and 10 antibody complexes of the S-protein (∼380,000 computed mutations), and validated the approach against diverse experimental binding/escape data of ACE2 and antibodies. The ACE2-antibody selectivity change caused by mutation (i.e., the differential change in binding to ACE2 vs. immunity-inducing antibodies) is proposed to be a key metric of fitness model, enabling systematic error cancelation when evaluated. In this model, new mutations become fixated if they increase the selective binding to ACE2 relative to circulating antibodies, assuming that both are present in the host in a competitive binding situation. We use this model to categorize viral mutations that may best reach ACE2 before being captured by antibodies. Our model may aid the understanding of variant-specific vaccines and molecular mechanisms of viral evolution in the context of a human host.

Cooperative and structural relationships of the trimeric Spike with infectivity and antibody escape of the strains Delta (B.1.617.2) and Omicron (BA.2, BA.5, and BQ.1)

Herein, we conducted simulations of trimeric Spike from several SARS-CoV-2 variants of concern (Delta and Omicron sub-variants BA.2, BA.5, and BQ.1) and investigated the mechanisms by which specific mutations confer resistance to neutralizing antibodies. We observed that the mutations primarily affect the cooperation between protein domains within and between protomers. The substitutions K417N and L452R expand hydrogen bonding interactions, reducing their interaction with neutralizing antibodies. By interacting with nearby residues, the K444T and N460K mutations in the SpikeBQ.1 variant potentially reduces solvent exposure, thereby promoting resistance to antibodies. We also examined the impact of D614G, P681R, and P681H substitutions on Spike protein structure that may be related to infectivity. The D614G substitution influences communication between a glycine residue and neighboring domains, affecting the transition between up- and -down RBD states. The P681R mutation, found in the Delta variant, enhances correlations between protein subunits, while the P681H mutation in Omicron sub-variants weakens long-range interactions that may be associated with reduced fusogenicity. Using a multiple linear regression model, we established a connection between inter-protomer communication and loss of sensitivity to neutralizing antibodies. Our findings underscore the importance of structural communication between protein domains and provide insights into potential mechanisms of immune evasion by SARS-CoV-2. Overall, this study deepens our understanding of how specific mutations impact SARS-CoV-2 infectivity and shed light on how the virus evades the immune system.

SARS-CoV-2 genomics and impact on clinical care for COVID-19

The emergence and worldwide spread of SARS-CoV-2 during the COVID-19 pandemic necessitated the adaptation and rapid deployment of viral WGS and analysis techniques that had been previously applied on a more limited basis to other viral pathogens, such as HIV and influenza viruses. The need for WGS was driven in part by the low mutation rate of SARS-CoV-2, which necessitated measuring variation along the entire genome sequence to effectively differentiate lineages and characterize viral evolution. Several WGS approaches designed to maximize throughput and accuracy were quickly adopted by surveillance labs around the world. These broad-based SARS-CoV-2 genomic sequencing efforts revealed ongoing evolution of the virus, highlighted by the successive emergence of new viral variants throughout the course of the pandemic. These genomic insights were instrumental in characterizing the effects of viral mutations on transmissibility, immune escape and viral tropism, which in turn helped guide public health policy, the use of monoclonal antibody therapeutics and vaccine development strategies. As the use of direct-acting antivirals for the treatment of COVID-19 became more widespread, the potential for emergence of antiviral resistance has driven ongoing efforts to delineate resistance mutations and to monitor global sequence databases for their emergence. Given the critical role of viral genomics in the international effort to combat the COVID-19 pandemic, coordinated efforts should be made to expand global genomic surveillance capacity and infrastructure towards the anticipation and prevention of future pandemics.

Antibody evasion associated with the RBD significant mutations in several emerging SARS-CoV-2 variants and its subvariants

Since the origin of the wild strain of SARS-CoV-2, several variants have emerged, which were designated as VOC, VOI, and VUM from time to time. The Omicron variant is noted as the recent VOC. After the origin of the Omicron variant on November 2021, several subvariants of Omicron have originated subsequently, like BA.1/2, BA.2.75/2.75.2, BA.4/5, BF.7, BQ.1/1.1, XBB.1/1.5, etc. which are circulated throughout the globe. Scientists reported that antibody escape is a common phenomenon observed in all the previous VOCs, VOIs, including Omicron and its subvariants. The mutations in the NTD (N-terminal domain) and RBD (Receptor-binding domain) of the spike of these variants and subvariants are responsible for antibody escape. At the same time, it has been noted that spike RBD mutations have been increasing in the last few months. This review illustrates significant RBD mutations namely R346T, K417N/T, L452R, N460K E484A/K/Q, and N501Y found in the previous emerging SARS-CoV-2 variants, including Omicron and its subvariants in high frequency and their role in antibody evasion and immune evasion. The review also describes the different classes of nAb responsible for antibody escape in SARS-CoV-2 variants and the molecular perspective of the mutation in nAb escape. It will help the future researchers to develop efficient vaccines which can finally prevent the pandemic.

Molecular dynamics simulations of the spike trimeric ectodomain of the SARS-CoV-2 Omicron variant: structural relationships with infectivity, evasion to immune system and transmissibility

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron is currently the most prevalent SARS-CoV-2 variant worldwide. Herein, we calculated molecular dynamics simulations of the trimeric spikeWT and SpikeBA.1 for 300 ns. Our results show that SpikeBA.1 has more conformational flexibility than SpikeWT. Our principal component analysis (PCA) allowed us to observe a broader spectrum of different conformations for SpikeBA.1, mainly at N-terminal domain (NTD) and receptor-binding domain (RBD). Such increased flexibility could contribute to decreased neutralizing antibody recognition of this variant. Our molecular dynamics data show that the RBDBA.1 easily visits an up-conformational state and the prevalent D614G mutation is pivotal to explain molecular dynamics results for this variant because to lost hydrogen bonding interactions between the residue pairs K854SC/D614SC, Y837MC/D614MC, K835SC/D614SC, T859SC/D614SC. In addition, SpikeBA.1 residues near the furin cleavage site are more flexible than in SpikeWT, probably due to P681H and D614G substitutions. Finally, dynamical cross-correlation matrix (DCCM) analysis reveals that D614G and P681H may allosterically affect the cleavage site S1/S2. Conversely, S2' site may be influenced by residues located between NTD and RBD of a neighboring protomer of the SpikeWT. Such communication may be lost in SpikeBA.1, explaining the changes of the cell tropism in the viral infection. In addition, the movements of the NTDWT and NTDBA.1 may modulate the RBD conformation through allosteric effects. Taken together, our results explain how the structural aspects may explain the observed gains in infectivity, immune system evasion and transmissibility of the Omicron variant.Communicated by Ramaswamy H. Sarma.

Structure adaptation in Omicron SARS-CoV-2/hACE2: Biophysical origins of evolutionary driving forces

Since its emergence, the COVID-19 threat has been sustained by a series of transmission waves initiated by new variants of the SARS-CoV-2 virus. Some of these arise with higher transmissivity and/or increased disease severity. Here, we use molecular dynamics simulations to examine the modulation of the fundamental interactions between the receptor binding domain (RBD) of the spike glycoprotein and the host cell receptor (human angiotensin-converting enzyme 2 [hACE2]) arising from Omicron variant mutations (BA.1 and BA.2) relative to the original wild-type strain. Our key findings are that glycans play a vital role at the RBD···hACE2 interface for the Omicrons, and the interplay between glycans and sequence mutations leads to enhanced binding. We find significant structural differences in the complexes, which overall bring the spike protein and its receptor into closer proximity. These are consistent with and attributed to the higher positive charge on the RBD conferred by BA.1 and BA.2 mutations relative to the wild-type. However, further differences between subvariants BA.1 and BA.2 (which have equivalent RBD charges) are also evident: mutations reduce interdomain interactions between the up chain and its clockwise neighbor chain in particular for the latter, resulting in enhanced flexibility for BA.2. Consequently, we see occurrence of additional close contacts in one replica of BA.2, which include binding to hACE2 by a second RBD in addition to the up chain. Although this motif is not seen in BA.1, we find that the Omicrons can directly/indirectly bind a down-RBD to hACE2 through glycans: the role of the glycan on N90 of hACE2 switches from inhibiting to facilitating the binding to Omicron spike protein via glycan-protein lateral interactions. These structural and electrostatic differences offer further insight into the mechanisms by which viral mutations modulate host cell binding and provide a biophysical basis for evolutionary driving forces.