The spike (S) glycoprotein of coronaviruses is essential for binding of the virus to the host cell at the beginning of the infection process. The target protein is also a major immunogen and a possible target for entry inhibitors. The SARS-CoV-2 spike (S) protein is a large type I transmembrane protein composed of two subunits, S1 and S2. The S1 subunit contains a receptor-binding domain (RBD) responsible for binding to the host cell receptor angiotensin-converting enzyme 2 (ACE2). Several mutants of the spike protein are known, including a novel SARS-CoV-2 lineage AY.1/AY.2/AY.3. Compared to the previously circulating variants, the mutations L452R and T478K of the SARS-CoV-2 Spike S1 (RBD) may cause a stronger affinity of the spike protein to hACE2 and also conferring an increasing ability to evade the hosts’ immune system. Furthermore, the Delta Plus variant has an additional K417N amino acid mutation. This mutation seems to have no significant impact on the clinical spectrum of disease and not more transmissible than Delta.
