The receptor binding domain (RBD) is located C-terminally within the S1 subunits of the spike (S) protein. The S protein forms a homotrimeric structure on the surface of the SARS-CoV-2 virus and binds to the angiotensin-converting enzyme 2 (ACE2) receptor of target cells. Recent studies have shown that the predominant activated form displays one RBD rotated upwards into an ACE2-accessible state and it is known that binding of RBD to ACE2 is a major contributor for interaction of the S protein with its target receptor. The SARS-CoV-2 RBD (insect cells) protein covers amino acids R319 to S591 of the spike protein and contains a His-tag and an AviTag™. Recombinant SARS-CoV-2 RBD