coronavirus non-structural protein 10This model represents the non-structural protein 10 (Nsp10) of alpha-, beta-, gamma- and deltacoronaviruses, including highly pathogenic betacoronaviruses such as Severe acute respiratory syndrome-related coronavirus (SARS-CoV), SARS-CoV2 (also called 2019 novel CoV or 2019-nCoV), and Middle East respiratory syndrome-related (MERS) CoV. CoVs utilize a multi-subunit replication/transcription machinery. A set of non-structural proteins (Nsps) generated as cleavage products of the ORF1a and ORF1ab viral polyproteins assemble to facilitate viral replication and transcription. Upon processing of the Nsp7-10 region by protease M (Mpro), the released four small proteins Nsp7, Nsp8, Nsp9, and Nsp10 form functional complexes with CoV core enzymes and thereby stimulate replication. Coronaviruses cap their mRNAs; RNA cap methylation may involve at least three proteins: Nsp10, Nsp14, and Nsp16. Nsp10 serves as a cofactor for both Nsp14 and Nsp16. Nsp14 consists of 2 domains with different enzymatic activities: an N-terminal ExoN domain and a C-terminal cap (guanine-N7) methyltransferase (N7-MTase) domain. The association of Nsp10 with Nsp14 enhances Nsp14's exoribonuclease (ExoN) activity, and not its N7-Mtase activity. ExoN is important for proofreading and therefore, the prevention of lethal mutations. The Nsp10/Nsp14 complex hydrolyzes double-stranded RNA in a 3' to 5' direction as well as a single mismatched nucleotide at the 3'-end, mimicking an erroneous replication product, and may function in a replicative mismatch repair mechanism. Nsp16 Cap-0 specific (nucleoside-2'-O-)-methyltransferase (2'OMTase) acts sequentially to Nsp14 MTase in RNA capping methylation, and methylates the RNA cap at the ribose 2'-O position; it catalyzes the conversion of the cap-0 structure on m7GpppA-RNA to a cap-1 structure. The association of Nsp10 with Nsp16 enhances Nsp16's 2'OMTase activity, possibly through enhanced RNA binding affinity. Additionally, transmissible gastroenteritis virus (TGEV) Nsp10, Nsp16, and their complex can interact with DII4, which normally binds to Notch receptors; this interaction may disturb Notch signaling. Nsp10 also binds 2 zinc ions with high affinity.