The SARS-CoV-2 spike glycoprotein is a type I membrane protein, which forms a trimer, anchored to the viral membrane by its transmembrane segment, while decorating the virion surface with it large ectodomain. It binds to the receptor angiotensin-converting enzyme 2 (ACE2) on a host cell and undergo large structural rearrangements to promote membrane fusion. The protein is heavily glycosylated with each protomer containing 22 N-linked glycosylation sites. The full-length S protein of the Wuhan-Hu-1 strain from the initial outbreak has 1273 amino acid residues, including a N-terminus signal peptide, a receptor-binding fragment S1 and a fusion fragment S2.