C-terminus of non-structural protein 3, including transmembrane and Y domains, from Severe acute respiratory syndrome-related coronavirus and betacoronavirus in the B lineage
This model represents the C-terminus of non-structural protein 3 (Nsp3) from betacoronavirus in the sarbecovirus subgenus (B lineage), including highly pathogenic human coronaviruses such as Severe acute respiratory syndrome-related coronavirus (SARS-CoV) and SARS-CoV2 (also called 2019 novel CoV or 2019-nCoV). This conserved C-terminus includes two transmembrane (TM) regions TM1 and TM2, an ectodomain (3Ecto) between the TM1 and TM2 that is glycosylated and located on the lumenal side of the ER, an amphiphatic region (AH1) that is not membrane-spanning, and a large Y domain of approximately 370 residues. Nsp3 is a large multi-functional multi-domain protein that is an essential component of the replication/transcription complex (RTC), which carries out RNA synthesis, RNA processing, and interference with the host cell innate immune system. In SARS-CoV and the related murine hepatitis virus (MHV), the TM1, 3Ecto and TM2 domains are important for the papain-like protease (PL2pro) domain to process Nsp3-Nsp4 cleavage. It has also been shown that the interaction of 3Ecto with the lumenal loop of Nsp4 is essential for ER rearrangements in cells infected with SARS-CoV or MHV. The Y domain, located at the cytosolic side of the ER, consists of the Y1 and CoV-Y subdomains, which are conserved in nidovirus and coronavirus, respectively. Functional information about the Y domain is limited; it has been shown that Nsp3 binding to Nsp4 is less efficient without the Y domain.