Buzz
Named variants still pose many mysteries
Viruses undergoing mutations and development are termed as variants. In the case of SARS-COV-2, the virus causing covid-19, they commenced spreading significantly in November 2020, with the emergence of the Alpha variant first identified in the UK. The Delta variant, currently dominating globally, was first detected in India at the end of 2020. The latest variant, Omicron, was identified for the first time in South Africa in November 2021.There is still much to discover about Omicron. Although initial evidence suggests that this variant spreads rapidly, further research is needed before answering whether it could replace the Delta strain. Omicron has around 30 mutations on the spike protein, the structure that attaches to the virus's surface and allows it to lock onto and enter human cells. About 20 other mutations operate in different positions on the virus, some of which may be dangerous. How these mutations enhance infectivity is still under investigation.
Survival Instinct
Viruses, like all living organisms, have their own life cycle. They are parasitic species, and their life cycle begins when a parent virus infects another organism and invades its cells to create copies of itself. In the case of SARS-CoV-2, this happens when it attaches to an enzyme called ACE2 found in the membrane of some human cells. SARS-CoV-2 then introduces its genetic material into the cell. This cellular invasion is facilitated by the spike protein.The essence that can lead to virus mutations originates from the inherent randomness in the process of creating copies of any entity, making errors inevitable. When host cells produce copies of SARS-CoV-2, errors occur. Most viruses cannot survive with these errors during replication. However, some viruses can not only survive but also thrive due to these changes, spreading more efficiently within their host populations. New variants must have advantages over old variants if they aspire to become dominant. These advantages can be gained in various ways, but for a respiratory disease like covid-19, one of the crucial factors is the transmission ability, or in other words, the virus's ease of spreading from one person to another.
Life is Change, Even for Viruses
One of the early mutations that increased infectivity is known as N501Y, sometimes referred to as 'Nelly.' It is one of eight mutations characteristic of the spike protein in the Alpha variant and is also found in Omicron. '501' signifies the change occurring at amino acid position 501 in the 1,273-chain that makes up the spike. The sequence and composition of these amino acids are determined by the corresponding gene sequence, hence '501' refers to both the position on the gene and the position on the amino acid chain.Due to the distinct chemical properties of different amino acids, this interchange affects the structure of the spike protein. This is because the distribution of electric charge on it changes, altering the shape of the protein slightly, as regions with a positive charge attract regions with a negative charge. Thanks to these dynamics, N501Y allows a crucial part of the spike to twist around 20 degrees, helping it find a more suitable point to bind with the ACE2 receptor. The result is a stronger binding, meaning any copy of the variant infiltrating the body is more likely to find its target and initiate replication. This enhances the transmission capability. Other mutations employ a similar 'trick,' releasing different parts of the spike in various ways to efficiently bind with ACE2.Changing the shape of the spike protein is not the sole method to increase infectivity. Ravindra Gupta, a molecular virologist at the University of Cambridge, and his colleagues argued that Delta's increased transmission ability is partly due to a mutation at position 681. This is a point on the spike where, after binding with ACE2, the protein splits in two. Dr. Gupta stated that, among other factors, P681R, supported by two other shape-changing mutations elsewhere, makes it easier for the virus to introduce its genetic material into host cells.
