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.1.1.7, also known as Alpha variant or variant of concern (VOC-202012/01), was first detected in November 2020 during the Covid-19 pandemic in the United Kingdom and rapidly spread globally, partly owing to the increased transmissibility compared to the wild type. The B.1.1.7 lineage (Alpha variant) differs from the wild type sequence by 23 amino acid mutations: 14 non-synonymous mutations, 3 deletions and 6 synonymous mutations. One of these mutations leads to an amino acid substitution (N501Y) in the RBD of the B.1.1.7 lineage (Alpha variant), which mainly contributes to the increased infectivity of B.1.1.7 as mutations in the RBD affect antibody recognition and ACE2 binding efficiency. The N501Y mutation also emerged independently in SARS-CoV-2 variants in the B.1.351 lineage (Beta variant) and P.1 linage (Gamma variant).
The SARS-CoV-2 RBD B.1.1.7 (HEK) protein covers amino acids R319 to S591 of the spike protein, contains the N501Y mutation, as well as a C-terminal His-tag and a N-terminal AviTag.