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Identification of the bona fide active center of influenza A virus polymerase acidic protein as the antiviral target

Tong, Y.; Xu, S.; Wang, X.; Zhang, L.; Tu, Y.; Wu, Y.; Du, S.; Wang, W.

2025-08-07 microbiology
10.1101/2025.08.06.669014 bioRxiv
Show abstract

The influenza virus PA protein, a core subunit of RNA polymerase, is critical for viral replication and a key antiviral target. Contrary to the prevailing view that its endonuclease active site resides in the N-terminal domain (PAn, residues 1-319), we identified a C-terminal truncation (PAc, 320-716) of H1N1 PA that retained high endonuclease activity, while PAn showed minimal activity. Crystal structural analysis revealed that PAc binds substrate RNA via the YDS motif (residues 393-395), with mutations abolishing RNA association. Surprisingly, baloxavir acid (BXA), a known PA inhibitor, specifically targeted PAc rather than PAn, supported by molecular docking showing higher binding affinity to PAc. Mutations at PAc-BXA interaction sites identified F707A as a potential drug resistance mutation. Virtual screening targeting PAc identified methotrexate as potent inhibitors (EC50 < 100 nM), which effectively suppressed viral replication in vitro and alleviated symptoms in influenza-infected mice. Our findings redefine PAs catalytic architecture and establish PAc as a novel platform for antiviral discovery, offering strategies to combat drug resistance through structure-guided inhibitor design.

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