The cytoplasmic domain of influenza M2 protein interacts with caveolin-1

The cytoplasmic domain of influenza M2 protein (M2c) consists of 54 amino acid (aa) residues from aa44 to aa97. In this paper, M2c and its deletion mutant M2cΔ47–55 were expressed using prokaryotic expression system. First, glutaraldehyde crosslinking assay showed that M2c had multimerization potential mediated by aa47–55. Then, M2c, instead of M2cΔ47–55, directed eGFP from the whole cell localization to a predominately perinuclear region in CHO cells, which indicated that aa47–55 of M2c mediated the localization. Moreover, M2c colocalized with caveolin-1 (Cav) when CHO cells were cotransfected with Cav. A caveolin-1 binding motif ΦxxxxΦxxΦ (Φ represents aromatic amino acid residues) in aa47–55 of M2c was found by sequence alignment and analysis. Further overlay ELISA result showed that M2c, but not M2cΔ47–55, bound to prokaryotically expressed cholesterol-free Cav2–101, which illustrated the interaction could be cholesterol-independent. That was the first report of cellular protein bound to M2c.