Influenza virus polymerase acidic protein (PA) endonuclease domain (PA-Nter)

The Influenza polymerase acidic protein (PA) endonuclease domain is a vital enzymatic component of the influenza virus RNA-dependent RNA polymerase (RdRp) complex, which consists of PA, PB1, and PB2 subunits (UniProt P03433). Located at the N-terminus of the PA protein, this domain is responsible for the 'cap-snatching' mechanism, a process where the virus cleaves the 5'-methylguanosine cap from host cellular pre-mRNAs to use as primers for its own mRNA synthesis (Dias et al., Nature, 2009). This activity is essential for viral replication, as it allows the virus to hijack the host's translation machinery for the production of viral proteins. The active site of the PA endonuclease contains two divalent metal ions, typically manganese or magnesium, which are critical for its catalytic function and serve as the primary binding site for inhibitors (PubMed: 19194459). Therapeutic agents like baloxavir marboxil target this site by chelating these metal ions, thereby inhibiting the endonuclease activity and effectively halting viral transcription (Hayden et al., NEJM, 2018). Because this domain is highly conserved across various influenza A and B strains, it is an attractive target for broad-spectrum antiviral therapy. However, the clinical utility of targeting this domain is challenged by the emergence of specific amino acid substitutions, such as the I38T mutation, which significantly reduce drug susceptibility (Uehara et al., Antiviral Research, 2020). Monitoring for these resistance markers is crucial for managing patient treatment and tracking the spread of resistant viral strains.

Other names

PA endonucleaseInfluenza A virus PA subunit N-terminal domainCap-dependent endonucleaseInfluenza virus PA-Nter

Inhibition of the cap-dependent endonuclease activity within the PA subunit of the viral RNA polymerase complex, preventing the cleavage of host pre-mRNAs and subsequent viral mRNA synthesis (Hayden et al., NEJM, 2018).