When the first coronavirus cases in Chicago appeared in January, they bore the same genetic signatures as a germ that emerged in China weeks before. But as Egon Ozer, an infectious-disease specialist at the Northwestern University Feinberg School of Medicine, examined the genetic structure of virus samples from local patients, he noticed something different.
A change in the virus was appearing again and again. This mutation, associated with outbreaks in Europe and New York, eventually took over the city. By May, it was found in 95 percent of all the genomes Ozer sequenced.
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. In the mutant virus, the genetic instructions for just one of those amino acids — number 614 — switched in the new variant from a “D” (shorthand for aspartic acid) to a “G” (short for glycine).
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 percent carry the mutation, officially designated D614G but known more familiarly to scientists as “G.”
The tiny mutation found in the dominant coronavirus variant Like all coronaviruses, SARS-CoV-2 has a series of characteristic spikes surrounding its core. These spikes are what allow the virus to attach to human cells.
A mutation affecting the virus’s spike protein changed amino acid 614 from “D” (aspartic acid) to “G” (glycine). Research suggests that this small change — which affects three identical amino acid chains — might make the spike protein more effective, enhancing the virus’s infectiousness.
“G” hasn’t just dominated the outbreak in Chicago — it has taken over the world. Now scientists are racing to figure out what it means.
At least four laboratory experiments suggest that the mutation makes the virus more infectious, although none of that work has been peer-reviewed. Another unpublished study led by scientists at Los Alamos National Laboratory asserts that patients with the G variant actually have more virus in their bodies, making them more likely to spread it to others.