SRPK1 facilitates IBDV replication by phosphorylating VP1 at S48.

Infectious Bursal Disease Virus (IBDV), a double-stranded RNA virus of the Avibirnavirus genus, causes significant vaccine failures in immunocompromised young poultry. The VP1 protein of IBDV undergoes post-translational modifications that are critical for viral RNA transcription, genome replication, and overall viral proliferation. Phosphorylation enhances the ability of the IBDV polymerase VP1 and facilitates viral replication, while the specific mechanisms underlying VP1 phosphorylation and its role in the IBDV life cycle remain largely unexplored. This study shows that SRPK1 phosphorylates VP1 at the serine 48 (S48) residue in the N-terminal SPSR motif, enhancing polymerase activity and promoting replication. During IBDV infection, VP1 recruits SRPK1 and co-localizes with it. Inhibiting or deleting SRPK1 greatly reduced VP1 polymerase activity, a leading to a decrease in viral replication. Mutant strains S48A and S48E displayed impaired replication, highlighting the crucial role of SRPK1-mediated phosphorylation in VP1 function. These findings emphasize the key role of SRPK1-mediated VP1 phosphorylation in IBDV replication, providing new insights into viral-host interactions and potential therapeutic targets.