SARS-CoV-2 S1 RBD

Spike (S) protein protrudes from the surface of the spherical virions and mediates virus entry into host cells. It consists of an ectodomain comprised of the S1 receptor-binding subunit and the S2 membrane fusion subunit, a transmembrane domain, and a short intracellular tail. The S1 subunit mainly consists of the N-terminal domain (NTD) and the C-terminal domain (CTD). The CTD directly engages the cellular receptor, human angiotensin-converting enzyme 2 (ACE2), and functions as the receptor-binding domain (RBD). RBD is composed of the core structure and the receptor-binding motif (RBM; residues 439-506) that is responsible for directly engaging the ACE2 receptor. The S protein on the SARS-CoV-2 virion forms trimers.