We have not chatted about COVID in a while. However, with the rapid increase in cases in certain parts of the country, I thought it might be time to share some of the newest information.
The virus has a new version with a single amino acid substitution: glycine for aspartic acid.
At a glance, the mutation seemed trivial. About 1,300 amino acids serve as building blocks for a protein on the surface of the virus. However, the location was significant. The switch occurred in the part of the genome that codes for the super important “spike protein” – that protruding structure that gives the coronavirus its crownlike profile. This spike allows it to enter the human cell the way a burglar picks a lock.
And its ubiquity is undeniable. Of the approximately 50,000 genomes of the new virus that researchers worldwide have uploaded to a shared database, about 70% carry the mutation known as “G” to scientists (official designation D614G).
HOW A VIRUS WORKS
SARS-CoV2 can be thought of as an extremely destructive burglar. Unable to live or reproduce on its own, it breaks into human cells and takes over their biological machinery to make thousands of copies of itself. That leaves a trail of damaged tissue and triggers an immune system response that for some people can be disastrous.
This replication process is messy. Even though it has a “proofreading” mechanism for copying its genome, the coronavirus frequently makes mistakes, or mutations. The vast majority of mutations have no effect on the behavior of the virus.
But since the virus’s genome was first sequenced in January, scientists have been on the lookout for changes that are meaningful. And few genetic mutations could be more significant than others. Particularly any mutations that affect the spike protein — the virus’s most powerful tool.
A MORE INFECTIOUS VIRUS?
Hyeryun Choe, a virologist at Scripps Research, has studied spike proteins and the way they bind to the ACE2 receptor since the severe acute respiratory syndrome outbreak in 2003.
The spike protein for SARS-CoV2 has two parts that don’t always hold together well. According to Choe, the virus that arose in China, the outer part frequently broke off. Equipped with this faulty lock pick, the virus had a harder time invading host cells.
“I think this mutation happened to compensate,” Choe said.
Studying both versions of the gene using a proxy virus in a petri dish of human cells, Choe and her colleagues found that viruses with the G variant had more spike proteins, and the outer parts of those proteins were less likely to break off. This made the virus approximately 10 times more infectious in the lab experiment.
The mutation does not seem to lead to worse outcomes in patients. Nor did it alter the virus’s response to antibodies from patients who had the D variant, Choe said, suggesting that vaccines being developed based on the original version of the virus will be effective against the new strain.
OTHER POSSIBLE EXPLANATIONS
A New York team offers a different explanation as to why the variant is so infectious. Neville Sanjana, a geneticist at New York University, suggests that the improvement is actually in the infection process. He hypothesized that the G variant is more efficient at beginning the process of invading the human cell and taking over its reproductive machinery.
Jeremy Luban, a virologist at the University of Massachusetts Medical School who has also been experimenting with the D614G mutation, has been drawn to a third possibility: His experiments suggest that the mutation allows the spike protein to change shape as it attaches to the ACE2 receptor, improving its ability to fuse to the host cell.
British researchers also found evidence that people with the G variant had more viral particles in their bodies. Although this higher viral load didn’t seem to make people sicker, it might explain the G variant’s rapid spread, the scientists wrote. People with more virus to shed are more likely to infect others.
Currently, these are all theories. Sometimes, what happens in the lab does not translate to the outside world. Time will tell. In the meantime, keep your networking group relatively small. Social distance with others and wear your mask (properly) in indoor public spaces. Make smart lifestyle choices to maintain and healthy and happy immune system. COVID is still here and still a threat.