Missing link in replication process of coronaviruses identified by LUMC researchers

6 August 2020• PRESSRELEASE

Coronaviruses such as SARS-CoV-2 drastically remodel infected cells by building special membrane structures that accommodate virus replication. LUMC researchers previously discovered that the genome of the virus is copied in these replication organelles. These structures seemed to be completely sealed, which made it puzzling how the newly made genomes could leave this compartment. Using electron microscopy, the researchers found a passage that is formed by a large viral protein. This structure is a potential new starting point for the development of antiviral drugs. The study is published in Science.

Researchers from the Departments of Cell and Chemical Biology and Medical Microbiology of the Leiden University Medical Center (LUMC) have been working together since the first SARS outbreak in 2003 to better understand the replication of coronaviruses. They focus on the 'remodeling' and damage caused by the replicating virus in the infected cell. The research is led by Dr. Montserrat Bárcena and Prof. dr. Eric Snijder.

Virus builds special compartment for genome replication

In a previously published study, the researchers showed that coronaviruses convert membrane structures of infected cells into apparently closed compartments in which the viral genetic material, the RNA, is copied. “These ‘replication organelles’ are surrounded by a double membrane layer and probably offer the best conditions for the viral genome copying process. They may also allow the virus to hide from certain cellular immune responses”, says Snijder.

The newly made virus RNA carries the code to make new virus proteins, and ultimately has to be packaged in new virus particles in order for the virus to spread. “This requires that the newly made RNA is exported from the replication organelles”, explains Barcena. Thus far, however, researchers did not know how this could happen.

Freezing cells

In the new study, PhD student Georg Wolff and his colleagues have used an advanced electron microscopy technique to analyze coronavirus replication organelles as close as possible to their natural state. “For this cryo electron microscopy approach, the infected cells were rapidly frozen in liquid nitrogen. Subsequently, an ion beam was used to free a layer of cell material thin enough to make the still frozen content visible at a high resolution using an electron microscope”, explains Wolff.

That turned out to be a good move. They discovered that the double membrane of the replication organelle contains an opening. “This opening is formed by a combination of viral proteins that form a pore that would allow the RNA to be exported”, says Barcena.

New starting point for the development of virus inhibitors

“This newly discovered connection between the replication organelle and the rest of the cell not only provides more insight into the organization of the replication process of coronaviruses, but also offers a new starting point for the development of antiviral drugs”, explains Snijder. Blocking this pore is likely to inhibit or arrest the multiplication of coronaviruses.

With this discovery, the research groups of Snijder and Bárcena have found one of the missing pieces in the puzzle of coronavirus replication. Follow-up research will have to show how the newly discovered structure functions and whether it is indeed a useful target for the development of coronavirus inhibitors.

Read the whole article 'A molecular pore spans the double membrane of the coronavirus replication organellein Science. 

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