Promising viral targets for a broad-spectrum virostatic agent
Vermehrungsmaschinerie des Fiebervirus SFTSV bis ins kleinste Detail analysiert
Die BMBF-Nachwuchsgruppe um Dr. Maria Rosenthal am Bernhard-Nocht-Institut für Tropenmedizin (BNITM) hat neue Erkenntnisse zu einem wichtigen Protein in der Vermehrungsmaschinerie des Fieber-Thrombozytopenie-Virus SFTSV, einem Bunyavirus, gewonnen. Gemeinsam mit Kooperationspartnern und mithilfe modernster Kryo-Elektronenmikroskopie hat die Gruppe die Molekülstrukturen in fünf verschiedenen funktionellen Zuständen bis in die Details sichtbar gemacht. Das untersuchte Protein ist für die Virusvermehrung von Bunyaviren notwendig und bietet so hervorragende Angriffspunkte für antivirale Wirkstoffe. Die Ergebnisse des von der Leibniz-Gemeinschaft geförderten Projekts sind in der Fachzeitschrift Nucleic Acids Research erschienen: doi: 10.1093/nar/gkac1249.
Image: The process of viral genome amplification by the SFTSV L-protein was stopped at different points and the 3D structure and binding of the viral RNA was analysed in detail. The L-protein is shown as a ribbon model in grey, the different RNA species are shown in different colours. The individual steps of the genome amplification process are labelled. The data obtained allow a mechanistic understanding of the process and an identification of important targets for antiviral drugs.
Globalisation, climate change, proximity to wildlife and the increasing number of resistant pathogens increase the risk for the global spread of infectious diseases. New introductions of arboviruses (viruses transmitted by insects) such as West Nile virus infections in Germany are increasingly being observed by research groups in the population of Central Europe as well.
The SFTS virus (SFTSV) is a virus with segmented single-stranded RNA. The carriers are ticks - thus the virus belongs to the arboviruses. In East Asia, the SFTS virus has been able to spread rapidly and is now endemic there. An SFTS virus infection can trigger the so-called "severe fever-with-thrombocytopenia syndrome". Typical symptoms are a high fever, fatigue and a deficit of white blood cells (leukopenia) and blood platelets (thrombocytopenia) up to multi-organ failure.
The potential danger to the population, for example through Bunyavirus epidemics, is highlighted by the World Health Organisation (WHO) and clarified in the WHO Research and Development Plan. There are no vaccines approved in Europe or effective medicines against Bunyavirus infections so far.
"This makes it all the more important that we explore and learn to understand the reproduction machinery of the different bunyaviruses down to the smallest detail," says junior research group leader Rosenthal.
Regulation of the virus multiplication machinery under the microscope
The research team of international scientists from several institutes has now analysed one of the most important building blocks of the SFTS virus replication machinery down to the nanometre scale, the so-called L-protein of the RNA polymerase enzyme essential for the virus.
Collaboration between BNITM research groups with EMBL* Grenoble and the LIV / UHH** laboratories at the Centre for Structural Systems Biology (CSSB) led to the joint discovery of how the SFTSV L-protein is active and regulated at the molecular level. For example, the L protein changes its shape when a certain RNA hook inserts itself like a key into the corresponding site (lock) of the L protein. Other important binding sites for RNA were also identified in the L protein. The research groups were also able to observe for the first time how inaccurate the viral polymerase is when copying RNA, i.e. how mutations occur.
"There are several sites in the L-protein structure that are essential for the different functions of the protein and can probably be blocked by drug substances. You can think of it as a series of little locks that have to be unlocked in the right order. Blocking one of these locks then has an inhibitory effect on the activity of the RNA polymerase and stops the virus from replicating," Rosenthal explains.
Translation in infection research: laying the foundations for application
Rosenthal has already published results in structural research for Lassa virus polymerase, describing different functional states (Nature Communications, 2021; DOI 10.1038/s41467-021-27305). Although Lassa and SFTS viruses differ significantly in many respects, they are genetically closely related and their polymerases - the propagation machinery - show similarities.
"We hope that these similarities between the viruses will make it possible to develop a kind of broad-spectrum virostatic agent that is effective against all these viruses," says Rosenthal. "Structural biology is important to understand in detail how these viruses work," she continues. "With this knowledge, we are developing strategies that could enable the treatment of diseases caused by bunyaviruses in the future."
In a highly competitive competition, the young scientist from the Department of Virology at BNITM had received over two million euros from the Federal Ministry of Education and Research (BMBF) in 2020 for precisely this research approach in structural biology.
"The first successes of a long-term local and European research cooperation are now materialising. We are convinced that the results will open up new possibilities for future antiviral therapies for Lassa fever," says Prof. Stephan Günther, Board Member and Head of the Department of Virology at BNITM.
* European Molecular Biology Laboratory
** Leibniz-Institut für Experimentelle Virologie (LIV) / Universität Hamburg (UHH) mit Laboren am Centre for Structural Systems Biology (CSSB)
Williams H.M., Thorkelsson S. R., et al.; Structural insights into viral genome replication by the severe fever with thrombocytopenia syndrome virus L protein. Nucleic Acids Research, 1-19, 2022: https://doi.org/10.1093/nar/gkac1249
Function of viral polymerase in virus replication
To understand the complicated mechanism of virus replication, structural biology focuses on one key component: viral polymerase. In an infected cell, this enzyme ensures that new viral building blocks are created and duplicates the genetic information of the virus. The genome copies are then packaged with the viral building blocks into new "virions" that can leave the cell and infect a new host. Determining the polymerase structure helps scientists understand how a virus replicates. And this information, in turn, gives researchers important clues for developing drugs that can stop the infection.
Partners with strong expertise in electron microscopy are Dr Emmanuelle Quemin, group leader at the Institute for Integrative Biology of the Cell (I2BC), France, and Prof Kay Grünewald from LIV / UHH with laboratories at CSSB in Hamburg. The research group led by Dr Stephen Cusack, head of EMBL Grenoble, focuses on the polymerase of various human pathogenic viruses, especially from the influenza virus group.
Funded by the Leibniz Association "Leibniz Competition". (Cooperative-Excellence)
The Leibniz Competition addresses the strategic goals of the Leibniz Association within the framework of the Joint Initiative for Research and Innovation. The measures motivate to conduct research and research infrastructures at the highest level and to make the resulting successes visible. With its time-limited funding, the Leibniz Competition provides incentives to further raise the profile of the Leibniz Association. In this way, it deliberately sets itself apart from measures taken by other funding organisations and institutional funding.
Dr Maria Rosenthal
Research Group Leader
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Dr Eleonora Schoenherr
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