Recombinant SARS-CoV-2 B.1.617 Spike Protein S1 (carrier-free) from BIOLEGEND

SARS-CoV-2 is a respiratory virus which causes coronavirus disease 2019 (COVID-19). The coronavirus spike (S) glycoprotein is a class I viral fusion protein on the outer envelope of the virion that plays a critical role in viral infection by recognizing host cell receptors and mediating fusion of the viral and cellular membranes. The S glycoprotein is synthesized as a precursor protein consisting of about 1,300 amino acids that is then cleaved into an amino (N)-terminal S1 subunit (about 700 amino acids) and a carboxyl (C)-terminal S2 subunit (about 600 amino acids). Three S1/S2 heterodimers assemble to form a trimer spike protruding from the viral envelope. The S1 subunit contains a receptor-binding domain (RBD) that can specifically bind to angiotensin-converting enzyme 2 (ACE2), the receptor on target cells. Triggered by receptor binding, proteolytic processing and/or acidic pH in the cellular compartments, the class I viral fusion protein undergoes a transition from a metastable pre-fusion state to a stable post-fusion state during infection, in which the receptor-binding subunit is cleaved, and the fusion subunit undergoes large-scale conformational rearrangements to expose the hydrophobic fusion peptide, induce the formation of a six-helix bundle, and bring the viral and cellular membranes close for fusion. The trimeric SARS coronavirus (SARS-CoV-2) S glycoprotein consisting of three S1-S2 heterodimers binds the cellular receptor angiotensin-converting enzyme 2 (ACE2) and mediates fusion of the viral and cellular membranes through a pre- to post-fusion conformation transition. SARS-CoV-2 B1.617 was initially identified in India. Sub-lineages were detected B.1.617.1 (kappa variant) and B.1.617.2 (delta variant), and B.1.617.3.  The three variants have the L452R and D614G substitutions in the spike receptor-binding domain and enhanced receptor binding affinity and transmissibility. B.1.617.2 became predominantly in April 2021, and it was considered to be 50% more transmissible than the B.1.1.7 (alpha, UK variant).