The receptor binding domain (RBD) locates 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 mutant strain B.1.351, also known as 501Y.V2 or Beta variant, was first identified during the Covid-19 pandemic in the Eastern Cape province of South Africa in December 2020 and rapidly spread globally partly owing to the increased transmissibility compared to the wild-type. The B.1.351 lineage (Beta variant) differs from the wild-type sequence by 21 amino acid mutations of which three key amino acid substitutions K417N, E484K and N501Y occur in the RBD. The N501Y mutation also emerged independently in SARS-CoV-2 variants in the B.1.1.7 lineage (Alpha variant) and P.1 lineage (Gamma variant). The B.1.351 lineage (Beta variant) is reported to have a higher infectivity due to its increased affinity to the ACE2 receptor and shows reduced susceptibility to neutralising antibodies.
The SARS-CoV-2 RBD B.1.351 (HEK) protein covers amino acids R319 to S591 of the spike protein, contains the N501Y, K417N and E484K mutations, as well as a C-terminal His-tag and a N-terminal AviTag™. Recombinant SARS-CoV-2 RBD B.1.351 (HEK)-Biotin is specifically biotinylated at a single site, preserving full functionality of the RBD.