Viral Condensates: Making it hard to replicate

Understanding how to harden liquid condensates produced by influenza A virus could accelerate the development of novel antiviral drugs.
  1. Billy Wai-Lung Ng  Is a corresponding author
  2. Stephan Scheeff
  3. Josefina Xeque Amada
  1. The Chinese University of Hong Kong, Hong Kong

Understanding how viruses infect cells, replicate, and subsequently spread through the body is crucial for developing effective antiviral therapies. During this process, most common viruses – including the one responsible for flu, influenza A virus – form membrane-less organelles called condensates which help the virus to assemble its genome and replicate (Li et al., 2022). While some small molecules can manipulate the properties of these condensates to prevent viruses from replicating (Risso-Ballester et al., 2021), more research is required to understand how to efficiently and specifically target selected condensates.

Influenza A virus is thought to induce condensates in order to help with genome assembly (Alenquer et al., 2019). Its genome comprises of eight RNA segments, each forming a viral ribonucleoprotein (vRNP) complex that is synthesized in the nucleus. Once formed, the vRNPs migrate to the cytosol where, with a host factor called Rab11a, they create condensates known as viral inclusions, which possess liquid-like properties (Noda and Kawaoka, 2010; Han et al., 2021). Now, in eLife, Maria João Amorim and colleagues – including Temitope Akhigbe Etibor as first author – report how the material properties of these viral inclusions are maintained and regulated in live cells infected with influenza A virus (Etibor et al., 2023).

The team (who are based at Instituto Gulbenkian de Ciência, European Molecular Biology Laboratory and Católica Biomedical Research Centre) monitored the structure and orientation of viral inclusions by measuring their number, shape, size, and density. How the inclusions moved and interacted with each other was also studied through live-cell imaging and by calculating their molecular stability (Banani et al., 2017). Etibor et al. then investigated the impact of different factors on the material properties of the viral inclusions, including temperature, the concentration of vRNPs and Rab11a, and the number and strength of interactions between vRNPs (Figure 1). This allowed them to determine which of these factors has the greatest effect, and how these pathways may be manipulated to develop a new antiviral approach.

Modulating the material properties of the viral inclusions formed by influenza A virus.

During infection, influenza A virus (red) enters host cells (blue) and replicates. To achieve this, two driving factors – viral ribonucleoproteins (vRNPs) and a protein called Rab11a – drive the formation of liquid condensates called viral inclusions (top middle inset). It is thought that hardening these viral inclusions (bottom middle inset) so that they become stiffer and less round will make it more difficult for viruses to replicate and assemble their genomes. Etibor et al. investigated how changes in temperature, the concentration of the driving factors, and the valency (i.e., the number/types of interactions among the vRNPs) affected the properties of influenza A virus inclusions. Raising the temperature and concentration of driving factors led to smaller and larger viral inclusions respectively, but had no effect on the material properties of the viral inclusions (top and middle right inset). Increasing the valency led to more rigid viral inclusions, which were unable to fuse together and lost many of their liquid characteristics (bottom right inset).

Image credit: Figure created with BioRender.

The experiments revealed that while changes in temperature and the concentration of vRNPs and Rab11a altered the size of the viral inclusions, the material properties of the inclusions remained mostly the same. These results are surprising as previous studies have shown that, in general, condensates strongly depend on these two factors. Etibor et al. noted that these findings may be specific to influenza A virus, as its condensates need to maintain liquid-like properties over a wide range of vRNP concentrations to replicate efficiently.

Next, Etibor et al. treated cells with nucleozin, a pharmacological modulator that has been shown to lower the viral load in patients with influenza A in preclinical studies (Kao et al., 2010). Nucleozin glues together nucleoproteins (the major components of vRNPs), expanding the number and type of interactions within individual vRNPs as well as between different complexes. The increased interactions stabilized the vRNPs and led to more rigid and less dynamic viral inclusions which did not dissolve following shock treatments and were less able to fuse together. This suggests that nucleozin hardens the material properties of viral inclusions by increasing interactions between vRNPs.

The team also showed that nucleozin stiffened viral inclusions in the lung cells of mice infected with influenza A virus, and helped speed up the mice’s recovery. Furthermore, nucleozin did not alter the level of other proteins in the cells of the mice, demonstrating the drug’s specificity against the virus.

In summary, Etibor et al. revealed how different factors influence the material properties of viral inclusions in both cells and mice infected with influenza A virus. Their findings suggest that stabilizing vRNP interactions shows the most promise for disrupting the function of viral inclusions, and highlight the potential of antiviral drugs that harden these condensates.


Article and author information

Author details

  1. Billy Wai-Lung Ng

    Billy Wai-Lung Ng is in the School of Pharmacy and Li Ka Shing Institute of Health Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong

    For correspondence
    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-2892-6318
  2. Stephan Scheeff

    Stephan Scheeff is in the School of Pharmacy, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong

    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-7791-9670
  3. Josefina Xeque Amada

    Josefina Xeque Amada is in the School of Pharmacy, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong

    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0009-0008-6847-7725

Publication history

  1. Version of Record published: April 28, 2023 (version 1)


© 2023, Ng et al.

This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.


  • 543
    Page views
  • 44
  • 0

Article citation count generated by polling the highest count across the following sources: Crossref, PubMed Central, Scopus.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Billy Wai-Lung Ng
  2. Stephan Scheeff
  3. Josefina Xeque Amada
Viral Condensates: Making it hard to replicate
eLife 12:e88044.
  1. Further reading

Further reading

    1. Microbiology and Infectious Disease
    Bo Lyu, Qisheng Song
    Short Report

    The dynamic interplay between guanine-quadruplex (G4) structures and pathogenicity islands (PAIs) represents a captivating area of research with implications for understanding the molecular mechanisms underlying pathogenicity. This study conducted a comprehensive analysis of a large-scale dataset from reported 89 pathogenic strains of bacteria to investigate the potential interactions between G4 structures and PAIs. G4 structures exhibited an uneven and non-random distribution within the PAIs and were consistently conserved within the same pathogenic strains. Additionally, this investigation identified positive correlations between the number and frequency of G4 structures and the GC content across different genomic features, including the genome, promoters, genes, tRNA, and rRNA regions, indicating a potential relationship between G4 structures and the GC-associated regions of the genome. The observed differences in GC content between PAIs and the core genome further highlight the unique nature of PAIs and underlying factors, such as DNA topology. High-confidence G4 structures within regulatory regions of Escherichia coli were identified, modulating the efficiency or specificity of DNA integration events within PAIs. Collectively, these findings pave the way for future research to unravel the intricate molecular mechanisms and functional implications of G4-PAI interactions, thereby advancing our understanding of bacterial pathogenicity and the role of G4 structures in pathogenic diseases.

    1. Microbiology and Infectious Disease
    2. Physics of Living Systems
    Ray Chang, Ari Davydov ... Manu Prakash
    Research Article

    Microsporidia are eukaryotic, obligate intracellular parasites that infect a wide range of hosts, leading to health and economic burdens worldwide. Microsporidia use an unusual invasion organelle called the polar tube (PT), which is ejected from a dormant spore at ultra-fast speeds, to infect host cells. The mechanics of PT ejection are impressive. Anncaliia algerae microsporidia spores (3–4 μm in size) shoot out a 100-nm-wide PT at a speed of 300 μm/s, creating a shear rate of 3000 s-1. The infectious cargo, which contains two nuclei, is shot through this narrow tube for a distance of ∼60–140 μm (Jaroenlak et al, 2020) and into the host cell. Considering the large hydraulic resistance in an extremely thin tube and the low-Reynolds-number nature of the process, it is not known how microsporidia can achieve this ultrafast event. In this study, we use Serial Block-Face Scanning Electron Microscopy to capture 3-dimensional snapshots of A. algerae spores in different states of the PT ejection process. Grounded in these data, we propose a theoretical framework starting with a systematic exploration of possible topological connectivity amongst organelles, and assess the energy requirements of the resulting models. We perform PT firing experiments in media of varying viscosity, and use the results to rank our proposed hypotheses based on their predicted energy requirement. We also present a possible mechanism for cargo translocation, and quantitatively compare our predictions to experimental observations. Our study provides a comprehensive biophysical analysis of the energy dissipation of microsporidian infection process and demonstrates the extreme limits of cellular hydraulics.