Recombinant SARS-CoV-2 Spike protein S1 subunit, encompassing amino acids 16-685. This protein contains three mutations of interest K417T, E484K and N501Y (found in the RBD domain of some variants of concern). The construct contains a C-terminal Avi-Tag™ followed by a His-tag (6xHis). The protein was enzymatically biotinylated using the Avi-Tag™ and affinity purified.