Influenza B virus M2 protein can functionally replace its influenza A virus counterpart in promoting virus replication

- Flu A M2 protein (AM2) can be functionally replaced by that of Flu B (BM2).
- Both AM2 and BM2 with extended cytoplasmic tail are functional.
- Compatibility between the ion channel and the cytoplasmic tail is critical for M2 function.
- M2 with higher ion channel activity may augment influenza virus replication.

The M2 protein (AM2 and BM2) of influenza A and B viruses function as a proton channel essential for viral replication. They also carry a cytoplasmic tail whose functions are not fully delineated. It is currently unknown whether these proteins could be replaced functionally in a viral context. Here, we generated single-cycle influenza A viruses (scIAV-ΔHA) carrying various M2-2A-mCherry constructs in the segment 4 (HA) and evaluated their growth in complementing cells. Intriguingly, the scIAV-ΔHA carrying AM2 and that bearing BM2 grew comparably well in MDCK-HA cells. Furthermore, while the virus carrying chimeric B-AM2 in which the BM2 transmembrane fused with the AM2 cytoplasmic tail produced robust infection, the one bearing the AM2 transmembrane fused with the BM2 cytoplasmic tail (A-BM2) exhibited severely impaired growth. Altogether, we demonstrate that AM2 and BM2 are functionally interchangeable and underscore the role of compatibility between transmembrane and cytoplasmic tail of the M2 protein.