NCoV’s ancestors may have been circulating in bats for decades undetected, and they are also capable of transmitting to humans.
RaTG13 is a corona virus that lives in the horseshoe bat’s body. Photo: Live Science.
To understand where nCoV comes from and how it is transmitted to humans, researchers need to trace its evolutionary history through the virus’s genome, encoded in ribonucleic acid (RNA). But the evolutionary history of CoV is complicated because corona viruses frequently exchange genetic material with each other. That exchange is known as genetic recombination, making it difficult for researchers to determine how nCoV was initially transmitted to humans. Some researchers have suggested that nCoV is transmitted directly from bats to humans while others have hypothesized it passes through an intermediate host such as pangolins.
In the new study published on July 28 in the journal Nature Microbiology, scientists for the first time identified fragments of RNA in the genome of nCoV that evolved as a complete sample without genetic recombination, according to Maciej. Boni, associate professor of biology at the University of Pennsylvania Infectious Disease Dynamism Center. They then compared these gene regions to those of the same corona viruses found in bats and pangolins. They found that nCoV is most closely related to another bat corona virus called RaTG13.
In a previous study, the researchers specifically looked at the genes responsible for the receptor binding domain (RBD) in the dendritic protein of nCoV, which allows the virus to bind to the ACE2 receptor in human cells and spread. infection. According to the results of that study, the protein spike RBD has more genetic similarities with a type of corona virus in pangolins (called Pangolin-2019) than RaTG13. There are two possible explanations for this: nCoV has evolved its ability to be transmitted to humans while in the pangolin, or they develop RBD through recombination with a virus in the pangolin.
However, in the new study, Boni et al. Found no evidence of recombination in the viral prickly protein-responsible gene. Instead, the genetic sequencing data reveals a third explanation. It is the gene that governs the dendritic protein and the ability of nCoV to infect human cells was passed from the common ancestor of nCoV, RaTG13 and Pangolin- 2019.
The team stressed that there is still the possibility that the pangolin or another species acts as a vector for the transmission of nCoV to humans. But their research indicates the ability to multiply in the upper respiratory tract in humans and the pangolin of the corona virus actually evolved from bats. Hence, nCoV can be transmitted directly from bat to person.
To determine when nCoV’s ancestors differentiated into RaTG13 and Pangolin-2019, the team identified mutations in the nucleotides, the molecules that make up the CON RNA. They then counted mutations in regions of the CoV genome that did not undergo recombination. Based on nCoV’s estimates of the annual spike rate, they calculated the differentiation time.
Researchers discovered more than a century ago, a strain of virus produced SARS-CoV-2, RaTG13 and Pangolin-2019. According to them, this strain may have all the amino acids needed in the receptor binding domain to infect human cells. Amino acids are the building blocks of proteins such as dendritic proteins.
At that time, the Pangolin-2019 virus split from its common ancestor. Then, in the 1960s and 1970s, this line split into two, creating the line RaTG13 and SARS-CoV-2. Between 1980 and 2013, RaTG13 lost the ability to bind to human receptors, but nCoV did not. “The nCoV line has circulated at bats for 40-70 years before transmitting to humans,” says Boni. By the end of 2019, someone accidentally came into contact with nCoV, leading to an outbreak of the disease.
(According to Live Science)