The SARS-CoV-2 spike or fusion protein is a trimer: a group of three units, each consisting of a receptor-binding subunit, S1, and a subunit responsible for fusion, S2. The three S1 and S2 ...

However, the F protein has a delicate structure that changes ... "Rational design of uncleaved prefusion-closed trimer vaccines for human respiratory syncytial virus and metapneumovirus," include ...