Scientists believe one of the most important areas of the spike is the receptor-binding domain, the specific part of the protein that allows the virus to latch onto a receptor on the surface of our cells, said Vaughn Cooper, a professor of microbiology and molecular genetics at the University of Pittsburgh. Receptors are like sockets or docking stations that allow proteins to interact with the cell. Once the virus gains entry to the cell, it can cause havoc, hijacking the cell’s genetic machinery and turning it into a virus-making factory.
Delta’s rapid spread is particularly surprising given it lacks two mutations that made earlier variants so scary.
Delta doesn’t have the N501Y spike mutation found in the alpha, beta and gamma variants, which enabled them to invade cells more successfully than the original virus. That mutation changed one amino acid — a building block of proteins — in the receptor-binding domain.
Delta also lacks the E484K mutation, which has made the gamma variant so worrisome. This genetic change, sometimes called “Eek,” allows the virus to spread even among vaccinated people.
(Scientists use the Greek alphabet to name variants of concern.)
“The ‘D’ in delta stands for ‘different’ and a ‘detour’ to a different genomic mutation path,” Topol said. “But it doesn’t mean ‘doom,’” he said, noting that existing COVID vaccines remain mostly effective against the delta variant.
Vaccines protect people from COVID by providing them with antibodies that attach themselves to the spike protein, preventing the virus from entering cells. By dramatically reducing the number of viruses that enter cells, vaccines can prevent people from developing severe disease and make them less infectious to others.
Delta does share mutations with other successful variants. Like all the identified variants in circulation, delta contains a spike mutation called D614G, sometimes known as “Doug,” which became ubiquitous last year.
Scientists think Doug increases the density of spike protein on the surface of viral particles and makes it easier for the virus to enter cells.
Delta also has a spike mutation called P681R, which closely resembles a mutation in the alpha variant that appears to produce higher viral loads in patients, Cooper said. People infected with delta have 1,000 times more virus in their respiratory tract, making them more likely to spread the virus when they sneeze, cough or talk.