Recombinant SARS-CoV-2 Spike protein, RBD (Receptor Binding Domain) encompassing amino acids 319-541. This protein corresponds to SARS-CoV-2 Variant B.1.617.2 also known as variant Delta originally identified in India, and contains mutations L452R and T478K. It was constructed with a C-terminal Avi-Tag™ followed by a His-tag (6xHis). The protein was enzymatically biotinylated using the Avi-Tag™ and affinity purified.