The fact that the S-protein sequence of the new coronavirus (SARS-CoV-2) contains an unique sequence “PRRA” not found in other coronaviruses is inserted at the boundary between the S1 and S2 domains. It has also been frequently pointed out that the presence of this sequence has increased the infectivity of this virus to humans.
There is a paper discussing about the presence of a staphylococcal enterotoxin-like sequence around the inserted “PRRA” sequence (661-685) of SARS-CoV-2, and its potential effect on hyperinflammation of COVID-19.
By binding the T cell receptors (TCR) to this bacterial toxin-like sequence, the resulting toxic shock syndrome might be behind of the severe hyperinflammation of COVID-19? It says. This inference was made from molecular structural analysis of proteins, and is expected to be tested in practice.
SEB represents staphylococcal enterotoxin and has a quite structure similar to the 661-685 sequence of SARS-CoV-2.