Taming the wild virus

M Ramesh

Why does the SARS-CoV-2 virus transmit so fast? A team of scientists from IIT-Madras decided to delve into this.

Coronaviruses are nothing unfamiliar to us. It is a family of viruses and, off and on, members of the family pay us visits. The SARS-CoV, for instance, troubled us in 2012, while another called NL63 often causes mild infections. They all differ in structure. Understanding the structure of a virus is important because that tells you how it would interact with — infect — a human cell.

Why then is SARS-CoV-2 more transmissible and lethal than the other family members? Scientists Michael Gromiha (team leader), Puneet Rawat and Sherly Jemimah, in collaboration with PK Ponnuswamy, former Vice-Chancellor of the University of Madras, have studied this aspect; their findings have been published in the international scientific journal Proteins: Structure, Function, Bioinformatics.

Basically, the team examined this question: If we have immunity for NL63, then is it possible that we may acquire some degree of immunity against wild viruses such as SARS-CoV-2? They tried to find an answer by looking into how the virus interacts with the human cell.

The SARS-CoV-2 virus enters a human cell through ‘ACE2 receptors’, which are enzymes that generate small proteins that are useful for the cell. The coronaviruses have horn-like projections, called spike proteins. The spike proteins bind to ACE2, like a key inserted into a lock, and the virus gains entry into the cell and infects it. The team led by Gromiha investigated how the spike proteins of different virus strains interact with the ACE2 receptors of human cells and how this affects their transmission and the severity of the disease.

The researchers studied aspects such as the area of interaction, hydrophobicity (water repelling property) and binding energy in the three coronaviruses SARS-CoV, SARS-CoV-2 and NL63. “The scientists have used different computational approaches to understand the sequence and structural differences among the spike proteins,” observes S Selvaraj, Assistant Professor at Bharathidasan University, another expert in the subject.

They learnt that NL63 is less harmful because all three aspects — interaction area, hydrophobicity and binding energy — are reduced compared with the other two viruses.

Importantly, the researchers characterised the binding site amino acids (“residues”) in the spike protein of these coronaviruses to identify conserved interactions with human ACE2 protein. This profiling of the binding site amino acids will help in designing novel inhibitors to prevent the binding of the spike protein to ACE2. “This study will help design a broad spectrum of therapeutics, which can effectively target ACE2 binding coronavirus strains,” Rawat told Quantum.

The team is now onto a deeper analysis of binding regions to know which kinds of mutation impact the binding of the viruses, and identify potential therapeutics against it.