Caspase cleavage of influenza A virus M2 disrupts M2-LC3 interaction and regulates virion production.

Influenza A virus (IAV) Matrix 2 protein (M2) is an ion channel, required for efficient viral entry and egress. M2 interacts with the small ubiquitin-like LC3 protein through a cytoplasmic C-terminal LC3-interacting region (LIR). Here, we report that M2 is cleaved by caspases, abolishing the M2-LC3 interaction. A crystal structure of the M2 LIR in complex with LC3 indicates the caspase cleavage tetrapeptide motif (SAVD) is an unstructured linear motif that does not overlap with the LIR. IAV mutant expressing a permanently truncated M2, mimicking caspase cleavage, exhibit defects in M2 plasma membrane transport, viral filament formation, and virion production. Our results reveal a dynamic regulation of the M2-LC3 interaction by caspases. This highlights the role of host proteases in regulating IAV exit, relating virion production with host cell state.