The virus that causes the coronavirus disease COVID-19 is causing a global health crisis that has not been known for years. SARS-CoV-2 is not the only coronavirus that affects humans and, in fact, other viruses of the same family are the cause of some types of common cold or more serious diseases such as Middle East respiratory syndrome (MERS ) and severe acute respiratory syndrome (SARS).
The problem with this new type of coronavirus is that it seems to be transmitted much more easily than the rest of its ‘brothers’. As reported by the World Health Organization (WHO), “the disease can spread from person to person through droplets from the nose or mouth that are thrown away when an infected person coughs or exhales. These droplets fall on objects and surfaces around the person, so others can get COVID-19 if they come in contact with these objects or surfaces and then touch their eyes, nose, or mouth. They can also be spread if they inhale the drops that a person with COVID-19 has spread by coughing or exhaling. “
In recent weeks, research teams from around the world have been striving to discover the molecular mechanisms that explain this high transmission capacity: what are the routes of entry of the new coronavirus to human tissues? “Understanding the transmission of the virus is key to its containment and future prevention,” says David Veesler, a virology researcher at the University of Washington in Seattle. At the end of February, his group published the results of a study with SARS-CoV-2 on the bioRxiv biomedical server, a platform that allows scientists to quickly disseminate their research while the peer review process lasts for publication in scientific journals. The usual review process is a mechanism that gives science rigor but can last for months and, in health emergencies like this one, hinders the flow of information between scientists , and that is why many groups are using it to expedite the search for solutions to the COVID-19 disease. In this work, Veesler’s team describes the type of bond that is established between the virus and the host cells and that triggers the infection.
Master key to enter human tissues
“To infect, viruses always use something that is essential for the cell, something that cannot mutate to defend itself,” explains José Aguilar Gavilán, researcher and professor of virology at the University of Córdoba. “To understand how a virus infects a cell we can use the analogy of the key and the lock. Coronaviruses have an envelope on which small spikes are located that give them the appearance of a crown and are called spicules. Well, these spicules are the entry key to the cells and, in the new coronavirus, unlike SARS or MERS, the key has much more affinity than that of the other coronaviruses . That means that they open the doors more easily, and therefore they are transmitted more quickly ”, indicates the expert.
Entry to multiple tissues
And not only that. The process by which the virus protein binds to the cell membrane is activated by specific enzymes, and in this case genomic analyzes have revealed that the virus master key has a site, or domain, that is activated by an enzyme of the host cell called furin . “This sequence that SARS-CoV-2 can recognize, and that others did not, is present in more tissues and in more cells. This means that the virus, apart from infecting more quickly, has the ability to penetrate through different areas, not only the respiratory one, and that it could even be transmitted by other routes ”, Aguilar explains.
The furin activation site “makes the new coronavirus very different from the one that causes SARS in terms of its entry into cells, and possibly affects the stability of the virus and therefore transmission,” explained Gary Whittaker. , a virologist at Cornell University (New York) in an article published in Nature . His team has also released another structural analysis of the coronavirus spike in the bioRxiv repository.
Other groups are demonstrating how the virus protein binds with a high affinity to certain cell receptors that could constitute potential therapeutic targets for developing treatments. In any case, experts recommend patience and prudence, since it will also be necessary to carry out studies in cell or animal models to verify the function of the activation site.
