Non-structural protein 14 (nsp14) exoribonuclease domain (nsp14-ExoN)

The SARS-CoV-2 exoribonuclease (ExoN) domain is a critical component of the viral non-structural protein 14 (nsp14), which functions as a proofreading enzyme during genome replication. Unlike most RNA viruses, coronaviruses possess a large genome that requires high-fidelity replication; ExoN provides this by identifying and removing misincorporated nucleotides or nucleoside analogs added by the RNA-dependent RNA polymerase (nsp12) (Source: UniProt P0DTD1; PubMed: 32464097). This domain belongs to the DEDD superfamily of exonucleases and requires the co-factor nsp10 for its enzymatic activation and stability (Source: PubMed: 33167430). In the context of COVID-19, ExoN is a high-priority therapeutic target because its inhibition can lead to 'error catastrophe' or significantly sensitize the virus to existing antiviral drugs like Remdesivir, which ExoN would otherwise excise from the viral RNA (Source: PubMed: 34314701). Beyond proofreading, nsp14 also contains a methyltransferase domain involved in RNA capping, though the ExoN domain specifically handles the 3'-5' hydrolytic activity (Source: PubMed: 32814559). Targeting this domain offers a strategy to reduce viral fitness and overcome drug resistance mechanisms inherent in the SARS-CoV-2 replication machinery.

Other names

SARS-CoV-2 nsp14ExoN3'-to-5' exoribonucleaseGuanine-N7-methyltransferase/3'-5' exoribonuclease nsp14

Inhibition of the 3'-to-5' exoribonuclease activity prevents the virus from removing mismatched nucleotides or nucleoside analog drugs from the nascent RNA strand, leading to lethal mutagenesis or enhanced drug efficacy.