SARS (2002) spike protein S-2P with RBD down in the inactive conformation. This has been stabilized in the prefusion conformation with two proline mutations. One protomer has its domains colored as follows:

 

Blue: N-Terminal Domain (NTD)

Green: Receptor Binding Domain (RBD)

Tan: Remainder of S1

Red: Remainder of S2

 

See also 3dpx-014102 for a related structure from SARS-CoV-2 with one RBD up in the active conformation.