middle domain of alpha- and beta-coronavirus Nonstructural protein 15 (Nsp15), and related proteins
Nidovirus endoribonucleases (NendoUs) are uridylate-specific endoribonucleases, which release a cleavage product containing a 2',3'-cyclic phosphate at the 3' terminal end. NendoUs include Nsp15 from coronaviruses and Nsp11 from arteriviruses, both of which may participate in the viral replication process and in the evasion of the host immune system. Coronavirus Nsp15 NendoUs have an N-terminal domain, a middle (M) domain and a C-terminal catalytic (NendoU) domain. Coronavirus Nsp15 from Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV), human Coronavirus 229E (HCoV229E), and Murine Hepatitis Virus (MHV) form a functional hexamer. This middle domain harbors residues involved in hexamer formation and in trimer stability. Oligomerization of Porcine DeltaCoronavirus (PDCoV) Nsp15 differs from that of the other coronaviruses; it has been shown to exist as a dimer and a monomer in solution.
Jiyao W et al.(2023). "The conserved domain database in 2023.",