The emergence of a new variant of coronavirus has sparked renewed interest in the part of the virus known as spike protein.
The new variant entails several peculiar changes to the ear protein compared to other closely related variants, and this is one of the reasons why it is more worrisome than other harmless changes to the virus we have observed before. New mutations can alter the biochemistry of the ear and can affect the transmission of the virus.
Spike protein is also the basis of current COVID-19 vaccines, which try to generate an immune response against it. But what exactly is spike protein and why is it so important?
Cell invaders
In the world of parasites, many bacterial pathogens or fungi can survive alone without a host cell becoming infected. But viruses can’t. Instead, they must enter cells to reproduce, where they use the cell’s own biochemical machinery to build new virus particles and spread to other cells or individuals.
Our cells have evolved to prevent these intrusions. One of the main defenses of cell life against invaders is its outer coating, which consists of a layer of fat that contains all the enzymes, proteins and DNA that make up a cell.
Due to the biochemical nature of fats, the outer surface is highly negatively charged and repellent. Viruses must cross this barrier to gain access to the cell.
As SARS-CoV-2 enters cells and reproduces. (Pislar et al., PLoS Pathog, 2020, CC BY)
Like cell life, coronaviruses themselves are surrounded by a fatty membrane known as an envelope. In order to enter the cell, the wrapped viruses use proteins (or glycoproteins, as they are often covered with slippery sugar molecules) to fuse their own membrane with that of the cells and make -is in charge of the cell.
The coronavirus ear protein is one of these viral glycoproteins. Ebola viruses have one, the flu virus has two, and the herpes simplex virus has five.
The architecture of the spike
The spike protein is composed of a linear chain of 1,273 amino acids, perfectly folded into a structure, which is nailed with up to 23 sugar molecules. Spike proteins like to bind together and three separate spike molecules bind together to form a “trimeric” functional unit.
The spike can be subdivided into different functional units, known as domains, that fulfill different biochemical functions of the protein, such as binding to the target cell, merging with the membrane, and allowing the spike to sit on the viral envelope.
The SARS-CoV-2 spike protein attaches to the approximately spherical viral particle, embedded in the envelope and projected into space, ready to cling to unsuspected cells. It is estimated that there are approximately 26 trimers per virus.
The ear protein is made up of different sections that perform different functions. (Rohan Bir Singh, CC BY)
One of these functional units binds to a protein on the surface of our cells called ACE2, causing the absorption of the virus particle and eventually the fusion of the membrane. The ear is also involved in other processes such as assembly, structural stability, and immune evasion.
Spike protein vaccine
Given the importance of spike protein for the virus, many vaccines or antiviral drugs are targeted at viral glycoproteins.
For SARS-CoV-2, the vaccines produced by Pfizer / BioNTech and Moderna instruct our immune system to make our own version of the spike protein, which occurs shortly after vaccination. The production of the ear inside our cells initiates the process of production of protective antibodies and T cells.
One of the most troubling features of the SARS-CoV-2 ear protein is how it moves or changes over time during the evolution of the virus. Encoded within the viral genome, the protein can mutate and change its biochemical properties as the virus evolves.
Most mutations will not be beneficial and will impede the functioning of spike protein or affect its function. But some can cause changes that give the new version of the virus a selective advantage in making it more transmissible or infectious.
One way it could occur is by a mutation in a part of the ear protein that prevents the protective antibodies from binding to it. Another way would be to make the peaks “more sticky” to our cells.
This is why new mutations that alter the way tip functions are of particular concern may affect the way we control the spread of SARS-CoV-2. New variants found in the UK and elsewhere have mutations in the ear and parts of the protein involved inside the cells.
Laboratory experiments will need to be conducted to determine if these mutations significantly change the rise, and how, and if our current control measures remain effective.
Connor Bamford, researcher, Virology, Queen’s University of Belfast.
This article is republished from The Conversation under a Creative Commons license. Read the original article.