| Description | Nidovirus endoribonucleases (NendoUs) are uridylate-specific endoribonucleases, which release a cleavage product containing a 2',3'-cyclic phosphate at the 3' terminal end. They are conserved among this order and a genetic marker of nidoviruses [ , , , ]. A feature of these viruses' evolutionary relationship is the organisation and processing of the genome, which is translated in two large precursor polyproteins (pp1a and pp1ab) from the replicase gene, that are proteolytically processed by virus proteases into 13 to 16 nonstructural proteins (NSPs) [].Proteins containing the NendoU domain include NSP15 from coronaviruses and NSP11 from arteriviruses, both of which participate in the viral replication process and in the evasion of the host immune system. Although they are similar and conserved, they only share 27% identical residues and show structural differences []. NSP11 has an N-terminal domain and a C-terminal NendoU catalytic domain. NSP11 functions as a dimer and Mg2 is dispensable for its activity. In Porcine reproductive and respiratory syndrome virus (PRRSV), NSP11 induces STAT2 degradation to inhibit interferon signaling. Mutagenesis studies revealed that the amino acid residue K59 located at the N-terminal domain of NSP11 is indispensable for inducing STAT2 reduction []. This domain is not conserved in those nidovirus branches that replicate in invertebrate hosts (Mesoniviridae, Roniviridae), suggesting specific roles in vertebrate hosts.The NendoU domain packs into two β-sheets which constitute the catalytic-site cleft located at one side of the domain. A group of small α-helices packed at the other side of the domain face the concave surface of the β-sheets. The active site, located in the shallow groove between the two β-sheets, carries the catalytic triad made of two histidines and a lysine [ , ].This entry represents the C-terminal NendoU domain of NSP15. NSP15 is encoded by ORF1a/1ab and proteolytically released from the pp1a/1ab polyprotein. This domain exhibits endoribonuclease activity designated EndoU, highly conserved in all known CoVs and is part of the replicase-transcriptase complex that plays important roles in virus replication and transcription [ , , ]. NSP15 is a Uridylate-specific endoribonuclease that cleaves the 5'-polyuridines from negative-sense viral RNA, termed PUN RNA either upstream or downstream of uridylates, at GUU or GU to produce molecules with 2',3'-cyclic phosphate ends [, , ]. PUN RNA is a CoV MDA5-dependent pathogen-associated molecular pattern (PAMP) []. | Name | NSP15, NendoU domain, coronavirus |
| Short Name | NSP15_NendoU_CoV | Type | Domain |
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