The SARS-CoV-2 spike glycoprotein (S) mediates the entry of the virus into target cells via its interaction with the angiotensin-converting enzyme 2 (ACE2) receptor, thereby initiating the infection. It forms a homotrimeric structure on the surface of the SARS-CoV-2 virus and represents the major target for diagnostic and therapeutic agents. The ectodomain of the S glycoprotein comprises the N-terminal S1 subunit, including the receptor binding domain (RBD) and the C-terminal S2 subunit. The ectodomain spans from aa12 to aa1213 followed by a transmembrane helix beginning at aa1214–aa1234. The C-terminus of the native protein is formed by a cytoplasmic domain spanning aa1235–aa1273.
The SARS-CoV-2 mutant strain B.1.617.2, also known as Delta variant, was first identified during the Covid-19 pandemic in India in late 2020. Due to increased transmissibility it spread rapidly around the globe. The B.1.617.2 lineage is defined by two amino acid deletions Δ156–157 and 8 amino acid substitutions T19R, G142D, R158G, L452R, T478K, D614G, P681R, and D950N occurring in the spike protein. Among them, the L452R mutation is suspected to confer increased affinity of the spike protein to the ACE2 receptor and may decrease recognition of the B.1.617.2 lineage by the immune system.
The Recombinant SARS-CoV-2 Spike-Prot B.1.617.2 (HEK) protein covers the ectodomain of the viral surface protein including amino acids V16 to K1211. It was engineered to contain the stabilizing proline substitutions at position K986P and V987P. The native sequence of the Furin cleavage site (RRAR at residues 682–685) was substituted by GSAG to further increase recombinant protein stability.
In addition, the SARS-CoV-2 Spike-Prot B.1.617.2 (HEK) protein contains the amino acid deletions Δ156–157 and the amino acid substitutions T19R, G142D, R158G, L452R, T478K, D614G, P681R, and D950N. The protein is extended at its C-terminus with a His-tag and an AviTag™. Recombinant SARS-CoV-2 Spike-Prot B.1.617.2 (HEK)-Biotin is specifically biotinylated at a single site, preserving full functionality of the protein.