This entry represents the N-terminal domain of the betacoronavirus-like trimeric spike glycoprotein. The distal S1 subunit of the coronavirus spike protein is responsible for receptor binding. S1 contains two domains; an N-terminal galectin-like doma ...
This entry represents the N-terminal domain of the betacoronavirus-like trimeric spike glycoprotein. The distal S1 subunit of the coronavirus spike protein is responsible for receptor binding. S1 contains two domains; an N-terminal galectin-like domain (NTD) and a receptor-binding domain (S1 RBD) also referred to as the S1 CTD or domain B. Either the S1 NTD or S1 RBD, or occasionally both, are involved in binding to host receptors. S1 NTD is located on the side of the spike trimer and mainly recognises sugar receptors [2]. For many betacoronaviruses (b-CoVs), for example mouse hepatitis virus (MHV), the RBD is located in the NTD. The structure of the MHV S1 NTD showed the same fold as human galectins (galactose-binding lectin), however it does not bind any sugar; instead, it binds to the carcinoembryonic antigen cell-adhesion molecule CEACAM1) through protein-protein interactions [2]. All three CEACAM21a-binding sites in MHV spikes can be fully occupied by CEACAM1a. It has been shown that CEACAM1a binding to the MHV spike weakens the interactions between S1 and S2 and facilitates the proteolysis of the spike protein and dissociation of S1 [2]. The homologous bovine CoV (BCov) S1 NTD also possesses a galectin fold but binds to sialic acid-containing moieties on host cell membranes, as does the NTD of three other group A b-Covs, namely human CoV (HCoV) OC43, avian b-CoV, and infectious bronchitis virus (IBV) [3]. Despite the S1 NTD of human respiratory b-CoV HKU1 being highly homologous to the NTDs of MHV and bovine CoV, it does not bind to either sugar or human carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) and the RBD is found instead in the S1 RBD domain [3].
