When a pathogenic virus or bacterium invades us, the immune system begins to synthesize antibodies – special proteins that recognize the pathogen. What do you mean find out? Antibodies bind to microbe-specific molecules; in the case of a virus, such a molecule would be a viral protein. When antibodies adhere to a viral protein, then, firstly, the protein itself becomes unable to perform its harmful functions, and secondly, immune cells see the target marked with antibodies and try to destroy it.
But antibodies do not recognize the entire viral protein as a whole, but only a part of it, a small structural fragment. Viruses are known to mutate quite easily. Changes appear in viral proteins that do not interfere with their work in any way and at the same time make them invisible to antibodies. Of course, then the immune system will understand that the virus is escaping from it, and we will have a new version of antibodies – now they will work against a new strain of the virus. But until they appear, this strain can cause a lot of trouble. Again, if we want to create a vaccine against a virus, we have to act with an eye to the fact that the virus will change, that it will have a new variant, and that the old vaccine will be useless.
In the case of the novel SARS-CoV-2 coronavirus, most of the diagnostic tests and vaccines available target the so-called S-protein. It sits in the envelope of the virus and helps it enter the cell. For the virus, the S-protein is extremely important, but at the same time, new mutations easily appear in the S-protein, which do not prevent the virus from entering cells. Accordingly, the question arises as to how effective a vaccine will be that targets immunity to the S-protein. Of course, here you can think about taking into account different variants of the S-protein when creating a vaccine, so that the immune system can recognize not just one strain, but several strains of the virus at once.
But besides the S-protein, there are others in the viral envelope. For example, an N-protein, or nucleocapsid protein, is associated with the RNA of a virus, which stores all of its genes. It is a packaging protein that helps compact RNA within the viral particle while protecting the RNA from some adverse effects. Staff Pennsylvania State University write in the magazine Nanoscalethat the N-protein is surprisingly constant among different types of coronaviruses. The researchers compared the amino acid sequences and three-dimensional structures of the N-proteins of the viruses SARS-CoV-2, SARS-CoV-1, MERS-CoV (which caused the outbreak of a very dangerous Middle East acute respiratory syndrome in the 2010s). Human coronaviruses were added to those that live in bats, pangolins and civets – all of these animals serve as a natural reservoir of the coronavirus and it is from them that the viruses are believed to have jumped to people.
In a viral particle, N-proteins are hidden in its depth, under the envelope, but during infection, N-protein molecules float freely in the blood, where they can be seen by immune cells; Obviously, N-proteins can also appear on the surface of cells infected with a virus – cells usually expose themselves to fragments of proteins that they have inside, so that immunity can distinguish a sick cell from a healthy one. That is, the immune system is quite capable of creating antibodies against the N-protein, and it actually creates them. N-proteins of different viruses mutate, like other viral proteins, and are somewhat different from each other. But the part of the molecule for which antibodies grab them is surprisingly constant in N-proteins. That is, antibodies against the N-protein of the SARS-CoV-2 virus can recognize the N-protein of the MERS virus or a virus taken from pangolin. We are talking specifically about human antibodies: the researchers took blood samples from patients with COVID-19 for the experiment.
It can be noted here that the authors of the work still did not compare the N-proteins of different strains of the SARS-CoV-2 coronavirus. However, if these proteins are the same for different types of coronaviruses, then it can be assumed that different strains within the same species (that is, different strains of SARS-CoV-2) will all the more be the same – in the sense that they will have the same are the areas for which antibodies grab them. If you create a vaccine, after which the immunity will recognize exactly the N-protein, then with its help it will be possible to protect oneself from many viral strains at once. Although, of course, for reliability, you still need to check how the N-proteins look in the new strains of SARS-CoV-2, which we hear more and more about lately.
Source: Автономная некоммерческая организация "Редакция журнала «Наука и жизнь»" by www.nkj.ru.
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