Viral Spike
Why do viruses need spike protein?
Lyubov Sokovikova, Hi-News
In the parasite world, many bacterial or fungal pathogens can survive on their own without infecting host cells. But viruses can't. Instead, they have to get inside cells to multiply, where they use their own biochemical mechanism to create new viral particles and spread to other cells or individuals. Like cellular life, coronaviruses themselves are surrounded by a fatty shell. To get inside the cell, they use proteins (or glycoproteins, since they are often covered with slippery sugar molecules) to fuse their own membrane with the cell membrane and thus capture the cell. One of these viral glycoproteins is the spike protein of coronaviruses. Given the emergence of new strains of the SARS-CoV-2 coronavirus, the interest of the general public in the spike protein has greatly increased. It turned out that the new variants of COVID-19 carry several specific changes in the spike protein compared to other closely related variants.
Spike proteins
One of the key biological characteristics of the SARS-CoV-2 coronavirus, like some other viruses, is the presence of spike proteins that allow these viruses to enter host cells and cause infection. Typically, the viral envelope of coronaviruses consists of three proteins, which include membrane protein (M), envelope protein (E) and spike protein (S).
Protein S, or spike protein, consists of 1160-1400 amino acids, depending on the type of virus. Compared to proteins M and E, which are mainly involved in virus assembly, protein S plays a crucial role in entering host cells and initiating infection. It is noteworthy that it is the presence of S-proteins on coronaviruses that leads to the appearance of spike-like protrusions on their surface.
Experts note that the S-proteins of coronaviruses can be divided into two important functional subunits, which include the N-terminal S1 subunit forming the spherical head of the S-protein, and the C-terminal S2 region directly embedded in the viral envelope. When interacting with a potential host cell, the S1 subunit recognizes and binds to receptors on the host cell, while the S2 subunit, which is the most conservative component of the S protein, is responsible for the fusion of the virus envelope with the host cell membrane.
It is noteworthy that without protein S, viruses like SARS-CoV-2 would never be able to interact with the cells of potential hosts, such as animals and humans. It is for this reason that protein S is an ideal target for research on vaccines and antiviral drugs. In addition to its role in the cell, the S-protein of viruses, in particular COVID-19, is the main inducer of neutralizing antibodies (nAbs). NABS are protective antibodies that are naturally produced by our immune system.
Spike protein and vaccines
Our cells have evolved to fend off invading viruses. One of the main protective forces of cellular life from invaders is its outer shell, which consists of a fat layer containing all the enzymes, proteins and DNA that make up the cell. Due to the biochemical nature of fats, the outer surface strongly repels viruses, which must overcome this barrier to gain access to the cell.
Given how important the spike protein is for the virus, the action of many antiviral vaccines or medications target viral glycoproteins. Moderna and Pfizer BioNTech's SARS-CoV-2 vaccines instruct our immune system to make its own version of the spike protein, which happens shortly after immunization. The production of spike protein inside our cells then triggers the production of protective antibodies and T cells.
As he writes One of the most important features of the SARS-CoV-2 spike protein is how it moves or changes over time during the evolution of the virus. The protein encoded in the viral genome can mutate and change its biochemical properties as the virus develops.
Most mutations are not beneficial and either stop the work of the spike protein, or do not affect its function. But some of them can cause changes that give the new version of the virus a selective advantage, making it more transmissible or infectious. One of the ways this can happen is a mutation in a part of the spike protein that prevents protective antibodies from binding to it. Another way is to make the spikes "stickier" for our cells.
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