[English]The spike protein is quite flexible. Especially, the receptor binding domain (RBD) on the top of the spike have both "closed" and "open" conformation. In the structure of "all close", all the three RBDs are closed. Whereas the "One open" structure has one "open" RBD, and "Two open" structure has two "open" RBDs. These "close"-"open" motion is important for binding to the human receptors and antibodies.
|all close One open Two open|