Biologically Relevant, Cationic Residues in Human Rhinovirus Stabilize Capsid-Bound RNA Duplexes, and Restrict Capsid Flexibility.

RNA-repelling Anionic Clusters in Human Rhinovirus Cooperate with Cationic Residues to Promote Virion Assembly and Restrain RNA Release.

Research on virus nucleic acid-protein interactions is important to understand infection and guide antiviral drug design. In previous studies we showed that the human rhinovirus (RV) genomic RNA is organized as a dodecahedral cage formed by 30 RNA duplex elements anchored to capsid concavities. We showed also that capsid-RNA duplex interactions include conserved tryptophans, neutral polar residues, and many positively charged residues that promote virion assembly and restrain RNA release by stabilizing the negatively charged RNA duplex structure. The present study expands our understanding of the capsid-RNA duplex interface in RV by addressing the structural and functional roles of conserved patches of negatively charged capsid residues interposed between each RNA duplex and its binding site at the capsid inner surface. The initial hypothesis was that electrostatic repulsion between anionic residues and RNA phosphates would lead to functional effects opposite to those previously found for cationic residues that can electrostatically attract RNA phosphates. In fact, those anionic residues do not oppose, but act together with cationic residues at the RNA duplex binding sites to promote virion assembly and restrain RNA release. Cryogenic electron microscopy analysis showed that negatively charged residues at the capsid-RNA duplex interfaces have a different structural role than positively charged residues, even though they all play similar functional roles. A tentative model is discussed to explain the functional effects of the complex distribution of negative and positive electrostatic potential found at capsid-RNA duplex interfaces in RV.

A capsid hinge region in European hepatitis E virus links mutations to genotype, virion surface properties, and environmental circulation

ABSTRACT Hepatitis E virus (HEV) exhibits genetic diversity associated with distinct public health outcomes and circulation patterns across interconnected human and environmental reservoirs. Most studies have focused on genome-wide diversity, revealing relationships between genotype, virulence, and dissemination routes. However, the role of localized mutations in the capsid protein (ORF2), which may influence the extracellular fate and ecology of HEV through changes in surface biological and physicochemical properties of virions, received limited attention. Here, we combined large-scale analysis of European HEV sequences, structural modeling, and physicochemical characterization to investigate such variations in ORF2. Analysis of ORF2 sequences on a genomic segment highly reported in GenBank, derived from patients and the environment, revealed recurrent mutation motifs (single H354Y and triple H354Y–G357S–V364I motifs) located in a conserved capsid hinge region connecting the middle (M) and protruding (P) domains of the protein. These motifs displayed distinct frequency patterns according to sequence sources and were associated with genotypes 3 and 1, respectively. AlphaFold-based modeling identified this region as a flexible interface between the M and P domains and indicated that mutations reduce predicted alignment error of the P domain relative to the overall protein model, consistent with altered exposure at the virion surface. In vitro analyses of synthetic peptides encompassing this critical region revealed increased hydrophobicity and structural rearrangements, supporting local modulation of capsid surface properties. Together, these results identify a structurally and physicochemically sensitive hinge region in the HEV capsid, suggesting a link between ORF2 sequence variations, genotype, virion surface properties, and environmental circulation. IMPORTANCE Hepatitis E virus (HEV) is a major cause of viral hepatitis worldwide, which is transmitted through complex, genotype-linked dissemination routes between humans, animals, and environmental waters. Understanding the circulation dynamics of HEV virions is essential for improving environmental surveillance, risk assessment, and public health strategies within a One Health approach. By combining genetic, structural, and physicochemical analyses, this study highlights specific mutation motifs in a hinge region of the ORF2 capsid protein likely to link distinct distribution patterns of HEV across environmental reservoirs to potential changes in virion surface properties. Such mutation motifs may serve as molecular signatures for exploring virus persistence and dissemination in environmental contexts. Overall, this work provides a new framework for connecting viral genetic variation to environmental behavior beyond traditional genotype classification. Hepatitis E virus (HEV) is a major cause of viral hepatitis worldwide, which is transmitted through complex, genotype-linked dissemination routes between humans, animals, and environmental waters. Understanding the circulation dynamics of HEV virions is essential for improving environmental surveillance, risk assessment, and public health strategies within a One Health approach. By combining genetic, structural, and physicochemical analyses, this study highlights specific mutation motifs in a hinge region of the ORF2 capsid protein likely to link distinct distribution patterns of HEV across environmental reservoirs to potential changes in virion surface properties. Such mutation motifs may serve as molecular signatures for exploring virus persistence and dissemination in environmental contexts. Overall, this work provides a new framework for connecting viral genetic variation to environmental behavior beyond traditional genotype classification.

Structural Overview of Herpesvirus Tegument Proteins

Structural insights into the nairovirus nucleoprotein endonuclease activity.

Nairoviruses are emerging tick-borne pathogens for which effective antiviral therapies are currently unavailable. Although nucleoproteins (NPs) are essential for viral genome encapsulation and have been extensively characterized at the structural level, whether they perform additional functions during viral replication remains unclear. Here, we investigated the NP of the representative nairovirus Tacheng tick virus 1 (TcTV1). We found that the TcTV1 NP binds to nucleic acids in a sequence-independent manner and assembles into tetramer-based ribonucleoprotein complexes upon nucleic acid binding. This assembly process is accompanied by a pronounced conformational rearrangement that facilitates NP polymerization. In addition to its role in RNA encapsulation, TcTV1 NP exhibits intrinsic endonuclease activity that does not require metal ions and preferentially cleaves unstructured single-stranded RNA, while structured RNA substrates are largely resistant to cleavage. Functional analysis indicates that the stalk domain of NP plays a central role in coordinating RNA binding, oligomerization, and access to the nuclease-active site, thereby influencing whether an RNA molecule is protected or degraded. Finally, we identified a small-molecule compound that interferes with both RNA binding and nuclease activity by targeting a conserved functional region of nairovirus NP. Together, these results reveal an expanded functional repertoire of nairovirus NPs and suggest that NP-mediated RNA discrimination may contribute to viral replication. Our findings also support the feasibility of targeting NP for the development of antiviral drugs against emerging nairoviruses.

Affinity-enhanced peptides delivered by mRNA–LNPs inhibit influenza A virus replication by disrupting the PA-PB1 interaction

Seasonal influenza causes up to 650,000 deaths annually and remains a persistent pandemic threat due to zoonotic strains crossing the species barrier. Current antivirals, which target neuraminidase or the viral polymerase, have limited efficacy and rapidly select for resistant variants, highlighting the urgent need for new therapeutic strategies. The heterotrimeric influenza polymerase (FluPol), comprising PA, PB1, and PB2 subunits, is essential for viral replication and harbors virus-specific protein-protein interfaces that are potential drug targets. We focused on the highly conserved PA-PB1 interface, where the N-terminal peptide of PB1 binds the PA C-terminal domain with high affinity. Disrupting this interaction abrogates polymerase function, halting viral replication. Using phage display, we identified PB1-derived peptides with enhanced affinity for PA and characterized their binding via biophysical methods and X-ray crystallography. Lead peptides efficiently disrupted the PB1-PA interaction and inhibited polymerase activity in cell-based assays. To address peptide delivery challenges, we expressed these inhibitors intracellularly from synthetic mRNA formulated in lipid nanoparticles, achieving robust inhibition of viral replication in cultured cells. This work establishes intracellularly expressed peptide inhibitors as a viable antiviral strategy and provides a generalizable framework for targeting essential protein-protein interactions of influenza and other RNA viruses.

The human papillomavirus L2 protein in the capsid is an ensemble of related structures poised to exit the virus particle

A structural model of L2 within the capsid is developed using cryo-EM single particle analysis of HPV16 pseudovirus capsids with and without the L2 protein combined with AlphaFold3 predictions and molecular dynamics simulations to develop a structural basis for understanding how L2 is organized in the capsid poised to initiate its action during virus entry.