Coronavirus structure offers clue to high infection rate

New York, May 6: Researchers studying the structure of the novel coronavirus that causes COVID-19 have found a unique feature in the virus that could explain its high transmissibility between people, an advance that may help develop new drugs against the disease.

The study, published in the Journal of Molecular Biology, identifies a structural loop in the SARS-CoV-2 spike protein, an area of the virus that facilitates its entry into cells.

In this loop, the researchers, including those from Cornell University in the US, assessed a sequence of four amino acids which make up the protein.

They said these amino acids are different from those in other known human coronaviruses part of this viral lineage. Analysing the lineage of SARS-CoV-2, the scientists showed that it shared properties of the closely related SARS-CoV-1 behind the 2002-03 SARS pandemic, and HCoV-HKU1, a highly transmissible but relatively benign human coronavirus. They said SARS-CoV-2 is both highly transmissible and lethal.

"It's got this strange combination of both properties," study co-author Gary Whittaker from Cornell University said. "The prediction is that the loop is very important to transmissibility or stability, or both," he added.

Whittaker and his colleagues focused on further studies of this structural loop and the sequence of four amino acids. Aside from primates, they said, cats, ferrets, and mink are the animal species most susceptible to the human novel coronavirus, SARS-CoV-2.

In order to infect a cell, they said features of the spike protein must bind with a receptor on the host cell's surface, and cats have a receptor binding site that closely matches that of humans. To date, the scientists said, infections in cats appear to be mild and infrequent, with no evidence that cats, in turn, infect humans.

Recent research had suggested that Malayan pangolins could be intermediate host for SARS-CoV-2, carrying the disease from bats to humans. However, the scientists speculated that both humans and pangolins could be final hosts from a different intermediate host.

"We hypothesise that despite having a common origin in bats, the relationship between pangolin coronaviruses and SARS-CoV-2 is not sufficient to support the claim that pangolins harbor the direct precursor to the currently circulating human SARS-CoV-2," the scientists reported in the study.

They said while the origin of the novel coronavirus has been found to be in bat reservoirs, there is still no definitive evidence of the possible intermediate host that could transmit the virus to humans. Whittaker added that studies probing into feline coronaviruses can provide further clues into SARS-CoV-2 and coronaviruses in general.