Coronaviruses such as SARS-CoV-2 dramatically grow the infected cell and make special membrane structures that are used for virus propagation. LUMC researchers previously discovered that the genome of coronaviruses is copied in those structures. These seemed completely closed off, so it was unknown how the newly made genome could come out of this compartment. The researchers have now discovered by means of electron microscopy a passage formed by a large viral protein. This finding offers a new starting point for the development of antiviral medicines. The study is published in Science.
Since the first SARS outbreak in 2003, researchers from the Department of Cell and Chemical Biology and Medical Microbiology at the Leiden University Medical Center (LUMC) have been working together to better understand the multiplication of coronaviruses. They focus, among other things, on the ‘cultivation’ and damage caused by the multiplying virus in the infected cell. The research is led by Dr. Montserrat Bárcena and Prof. Eric Snijder.
Virus builds special compartment for genome replication
In Previous research the researchers showed that coronaviruses convert the membrane structures of infected cells into seemingly closed compartments in which the viral genetic material, the RNA, is copied.
“These ‘replication organelles’ are surrounded by a double membrane and probably offer the best conditions for copying the viral genome. They may also allow the virus to hide from certain immune responses of the infected cell. ”, says Snijder.
The newly made virus RNA carries the code to make new virus proteins, and is eventually packed in new virus particles so that the virus can spread.
“This requires the new RNA to be exported from the replication organelles”, says Bárcena. Until now, researchers just didn’t know how this was possible.
Freezing cells
In the new study, PhD student Georg Wolff and colleagues used an advanced electron microscopy technique to study the replication organelles of the coronavirus under the most natural conditions.
“For this so-called cryo-electron microscopy, infected cells were frozen at lightning speed in liquid nitrogen. An ion beam then released a layer of cell material thin enough to reveal the still frozen contents with a high-resolution electron microscope. ”Wolff says.
That turned out to be a good move. Wolff and colleagues discovered that the replication organelle’s double membrane contains a passageway.
“This opening is formed by a combination of viral proteins that form a pore through which the new RNA could leave the compartment”, stelt Bárcena.
New starting point for the development of virus inhibitors
“This discovered connection between the 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 medicines”, Snijder explains.
Blocking this transport route 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 puzzle pieces in the replication puzzle of corona viruses. 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.
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