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The reason why the covid-19 rampage has slowed down in India could have very well been discovered by Indian scientists. You see, according to a study deficiency of a lung-protecting protein in the Caucasian population may have made Europe and North America more susceptible to the spread of a coronavirus variant as compared to Asia.
The study, published in the journal Infection, Genetics and Evolution, assessed the global spread of the coronavirus variant with the D614G mutation, which is the predominant lineage infecting North America and European populations.
This variant spread so rapidly that in just 10 weeks between February and March 2020 over 64.11% of globally infected individuals were identified to carry the mutant virus starting from only 1.95% in January.
However, the researchers, including those from the National Institute of Biomedical Genomics (NIBMG) in Kalyani, West Bengal, said this subtype took a significantly longer time to reach a 50% relative frequency in East Asia—5.5 months—compared to the 2.15 months it took in Europe, and the 2.83 months it took in North-America.
According to the scientists, a deficiency of the protein Alpha-antitrypsin (AAT) across the populations of Europe and North-America is one of the main factors that explain the rapid spread of this variant in the two continents compared to its transmission in Asia.
“For the coronavirus to enter cells, its spike protein binds with the ACE2 receptor in human cells, and the human enzyme TMPRSS2 cleaves at the junction of two subunits S1 and S2 of the protein, enabling the virus to fuse with the cell,” said study corresponding author Nidhan K Biswas from NIBMG.
“But due to the D614G mutation in the spike protein, the virus gained an additional cleavage site which enables it to fuse better with cells,” Biswas told PTI.
In lineages of the coronavirus carrying the D614G mutation, the 614th molecule of the virus spike protein—aspartic acid—denoted by D is replaced by the molecule glycine, noted as G.
“Instead of one cleavage site, the mutated virus has two such sites, and it can take dual advantage of this and enter cells more easily,” Biswas explained.
Based on the current study, he said this site in the virus is cleaved by the host protein neutrophil elastase which is normally involved in clearing up bacterial infections in the lungs.
The levels of the elastase molecules in the body are naturally kept in check by AAT whose main function is to protect the lungs from inflammation and tissue damage, the study noted.
“The issue is that if we have high neutrophil elastase then it also creates more damage to the lung cells. So there is a balance mechanism via the AAT enzyme that already exists by nature in everyone’s lungs,” Biswas explained.
He explained that the lack of this protein makes it much easier for the neutrophil elastase molecule to act on the virus spike subunits, resulting in a significantly faster spread of this mutant.
“The issue is that individuals with AAT deficiencies have high neutrophil levels and if they are infected with the SARS-CoV-2 virus with the D614G mutation, their cells can quickly take the virus up and into the whole system,” the NIGMB scientist explained.
The researchers believe this finding, along with other social factors may explain the differential geographical/ethnic spread of 614G.