Charge Matters: Mutations in Omicron variant favor Binding to Cells

Evidence is strengthening to suggest that the novel SARS‐CoV‐2 mutant Omicron, with its more than 60 mutations, will spread and dominate worldwide. Although the mutations in the spike protein are known, the molecular basis for why the additional mutations in the spike protein that have not previously occurred account for Omicron's higher infection potential, is not understood. We propose, based on chemical rational and molecular dynamics simulations, that the elevated occurrence of positively charged amino acids in certain domains of the spike protein (Delta: +4; Omicron: +5 vs. wild type) increases binding to cellular polyanionic receptors, such as heparan sulfate due to multivalent charge‐charge interactions. This observation is a starting point for targeted drug development.

Characterization of Human Parainfluenza Virus Receptor Using Terminal Sialic Acid Linkage-Modified Cells

Human parainfluenza virus type 1 (hPIV1) and type 3 (hPIV3) are respiratory pathogen viruses that bind to terminal sialic acids of glycoconjugates on the cell surface hemagglutinin-neuraminidase glycoprotein. Sialic acid residues are linked to the galactose residue primarily by α2,3 or α2,6 linkages on the terminal of glycoprotein or glycolipids. One of the major determinants of pathogenicity or tissue tropism is virus binding or infection specificity for each sialyl linkage. Sialic linkage-modified human blood cells or mammalian cells that mainly have α2,3- or α2,6-linked sialic acid residues on the surface can be prepared by treatment with linkage-specific sialidases or sialyltransferases. These linkage-modified cells can be used in hemagglutination assays to estimate virus particles' binding specificity, hemadsorption assays to estimate virus glycoproteins' binding specificity, and virus infectivity assays. These methods contribute to identifying the specificity of sialic acid lineage recognition of the hPIV or other sialic acid-binding viruses.

The diverse roles and dynamic rearrangement of vimentin during viral infection

Epidemics caused by viral infections pose a significant global threat. Cytoskeletal vimentin is a major intermediate filament (IF) protein, and is involved in numerous functions, including cell signaling, epithelial-mesenchymal transition, intracellular organization and cell migration. Vimentin has important roles for the life cycle of particular viruses; it can act as a co-receptor to enable effective virus invasion and guide efficient transport of the virus to the replication site. Furthermore, vimentin has been shown to rearrange into cage-like structures that facilitate virus replication, and to recruit viral components to the location of assembly and egress. Surprisingly, vimentin can also inhibit virus entry or egress, as well as participate in host-cell defense. Although vimentin can facilitate viral infection, how this function is regulated is still poorly understood. In particular, information is lacking on its interaction sites, regulation of expression, post-translational modifications and cooperation with other host factors. This Review recapitulates the different functions of vimentin in the virus life cycle and discusses how they influence host-cell tropism, virulence of the pathogens and the consequent pathological outcomes. These insights into vimentin-virus interactions emphasize the importance of cytoskeletal functions in viral cell biology and their potential for the identification of novel antiviral targets.

Spiky nanostructures for virus inhibition and infection prevention

The outbreak of a novel highly infectious virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has aroused people's concern about public health. The lack of ready-to-use vaccines and therapeutics makes the fight with these pathogens extremely difficult. To this point, rationally designed virus entry inhibitors that block the viral interaction with its receptor can be novel strategies to prevent virus infection. For ideal inhibition of the virus, the virus-inhibitor interaction has to outperform the virus-host interaction. In our view, the morphology of the inhibitor should be carefully designed to benefit virus-inhibitor binding, especially that the surfaces of viruses are mostly rough due to the existence of surface proteins for receptor-binding. In this perspective article, we would like to discuss the recent progress of designing inhibitors with spiky topography to maximize the interactions between viruses and inhibitors. We also would like to share our idea for the future study of inhibitors to prevent virus infection.

Probing ligand-receptor bonds in physiologically relevant conditions using AFM

Cell surface receptors, often called transmembrane receptors, are key cellular components as they control and mediate cell communication and signalling, converting extracellular signals into intracellular signals. Elucidating the molecular details of ligand binding (cytokine, growth factors, hormones, pathogens,...) to cell surface receptors and how this binding triggers conformational changes that initiate intracellular signalling is needed to improve our understanding of cellular processes and for rational drug design. Unfortunately, the molecular complexity and high hydrophobicity of membrane proteins significantly hamper their structural and functional characterization in conditions mimicking their native environment. With its piconewton force sensitivity and (sub)nanometer spatial resolution, together with the capability of operating in liquid environment and at physiological temperature, atomic force microscopy (AFM) has proven to be one of the most powerful tools to image and quantify receptor-ligand bonds in situ under physiologically relevant conditions. In this article, a brief overview of the rapid evolution of AFM towards quantitative biological mapping will be given, followed by selected examples highlighting the main advances that AFM-based ligand-receptor studies have brought to the fields of cell biology, immunology, microbiology, and virology, along with future prospects and challenges. Graphical abstract.

Multiple antiviral approaches of (-)-epigallocatechin-3-gallate (EGCG) against porcine reproductive and respiratory syndrome virus infection in vitro

Porcine reproductive and respiratory syndrome virus (PRRSV) remains an economically important pathogen in the global pig industry, effective measures to control the virus are still lacking. (-)-Epigallocatechin-3-gallate (EGCG), the most abundant and bioactive catechin in green tea, has been reported to have antiviral effect against the diverse groups of viruses. In this study, the comprehensive anti-PRRSV activity of EGCG was investigated using various in vitro assays. EGCG effectively inhibited PRRSV infection and replication in porcine alveolar macrophages (PAMs), regardless of whether it was administrated pre- or post-infection, and the cytotoxicity to PAMs was low. Next, anti-PRRSV approaches of EGCG were characterized in MARC-145 cells. EGCG was demonstrated to be able to significantly prevent PRRSV from infecting MARC-145 cells either through blocking of EGCG-treated viruses docking to susceptible cells involving a direct virus-EGCG interaction or by blocking of the infective virus binding to EGCG pre-treated cells via triggering down-regulation of viral receptors and/or related proteins required for infection. In addition, PRRSV replication was suppressed in MARC-145 cells treated with EGCG post-infection, likely because of down-regulation of pro-inflammatory cytokines, such as TNF-α, IL-6 and IL-8. Taken together, these data showed that treatment of primary PAMs with EGCG can inhibit PRRSV infection and revealed that multiple antiviral approaches of EGCG operate in PRRSV-susceptible MARC-145 cells.

The structural proteins of epidemic and historical strains of Zika virus differ in their ability to initiate viral infection in human host cells

Mosquito-borne Zika virus (ZIKV) recently emerged in South Pacific islands and Americas where large epidemics were documented. In the present study, we investigated the contribution of the structural proteins C, prM and E in the permissiveness of human host cells to epidemic strains of ZIKV. To this end, we evaluated the capacity of the epidemic strain BeH819015 to infect epithelial A549 and neuronal SH-SY5Y cells in comparison to the African historical MR766 strain. For that purpose, we generated a molecular clone of BeH819015 and a chimeric clone of MR766 which contains the BeH819015 structural protein region. We showed that ZIKV containing BeH819015 structural proteins was much less efficient in cell-attachment leading to a reduced susceptibility of A549 and SH-SY5Y cells to viral infection. Our data illustrate a previously underrated role for C, prM, and E in ZIKV epidemic strain ability to initiate viral infection in human host cells.

KSHV attachment and entry are dependent on αVβ3 integrin localized to specific cell surface microdomains and do not correlate with the presence of heparan sulfate

Cellular receptors for KSHV attachment and entry were characterized using tyramide signal amplification (TSA)-enhanced confocal microscopy. Integrins αVβ3, αVβ5 and α3β1 were detected on essentially all the actin-based cell surface microdomains that initially bind KSHV, while the presence of CD98 and heparan sulfate (HS), the putative attachment receptor, was more variable. KSHV bound to the same cell surface microdomains with and without HS indicating that initial attachment of KSHV is not dependent on HS and that receptors other than HS can mediate attachment. A human salivary gland (HSG) epithelial line was identified, which lacks αVβ3 but expresses high levels of HS, α3β1 and other putative KSHV receptors. These cells were resistant to KSHV binding and infection. Reconstitution of cell surface αVβ3 rendered HSG cells highly susceptible to KSHV infection, demonstrating a critical role for αVβ3 in the binding and entry of KSHV that is not shared with other proposed receptors.