Why is the Covid 19 virus on the rise as winter approaches? The most obvious reason is that when temperatures drop we tend to congregate inside buildings with less ventilation, increasing the risk of transmission. But for researchers at the University of Illinois, the seasonality of the epidemic is also explained by the ability of the virus to detect temperature changes and adapt to them.
According to their latest work, SARS-CoV-2 would have a kind of sensor located in the NTD domain (N-terminal domain) located on the side of the spike protein. This structure, which belongs to the class of lectins, would be sensitive to the environment and would trigger, under certain cool conditions, modifications helping the virus to infect the target cells.
“Imagine the virus as a small jar, with flaps at the top. When the temperature is high, it stays completely closed and cannot shed its infectious contents. But when the flaps recognize a host cell in cold, dry conditions, it opens, releasing molecules (peptides) promoting the fusion of viral and cellular membranes “, explains Gustavo Caetano-Anollés, researcher in the laboratory of bioinformatics of evolution at the University of Illinois.
Limited offer. 2 months for 1 € without commitment
–
Better predict contamination peaks
Surprisingly, corals played a role in this discovery. In 2019, Chinese researchers highlighted the role of certain proteins – galectins – in the bleaching of these emblematic species. Outside of a temperature band of between 25 and 30 degrees, these environmentally sensitive structures seemed less effective at recognizing dinoflagelleas, microorganisms with which corals live in symbiosis. These results have caught the attention of researchers in Illinois. Over several months, they sifted through tens of thousands of Sars-CoV-2 genomes and found structures similar to galectin in the spike protein.
Scientists now believe that these act as sensors: they sense outside conditions and when these are neither too hot nor too humid, they cause changes in the spike protein. “Remarkably, the mutations often concern these structures of the galectin type because they help the virus to bypass or reduce the effectiveness of the defenses developed by its host”, estimates Gustavo Caetano-Anollés. It’s akin to the spaghetti technique, which involves throwing pasta against a wall to see if it sticks to the vertical surface or not: to keep spreading, a virus is constantly trying new combinations.
L’application L’Express
To follow the analysis and decryption wherever you are
–
Download the app
–
–
These attempts may seem risky, but they obey a seasonal pattern. Because in general, the number of mutations bursts in winter, demonstrate the authors of the study, supporting tables. Thus, the prevalence of variants, that is to say their proportion in the sequencing is systematically higher during the months when the temperature is cooler, whether in the northern hemisphere or in the southern hemisphere. This is particularly true for the modifications made within the NTD domain. The researchers now hope that this new data will make it possible to better predict contamination peaks but also to refine the measures taken to fight the epidemic. They evoke, for example, the thorny case of schools: should they be closed during a period of strong spread of the virus, or should they be kept open? France has chosen the second option, with the risk – limited by barrier gestures – of seeing new variants appear.
