Conformation and Membrane Topology of the N-Terminal Ectodomain of Influenza a M2 Protein

The N-terminal ectodomain of the influenza A M2 protein is a target for universal influenza vaccine development and novel antiviral strategies. Despite the significance of this domain, it is poorly understood and most structural studies of the M2 protein have disregarded the N-terminal ectodomain in their analyses. Here we report conformational properties and insight into membrane topology of sites along the N-terminal ectodomain. Full-length M2 protein is embedded in lipid bilayer nanodiscs and studied using site-directed spin labeling electron paramagnetic resonance spectroscopy. Results are consistent with a turn in the middle of the ectodomain that changes in proximity to the membrane surface upon the addition of cholesterol or drug. Similar to other domains of M2 protein, lineshape analysis suggests that the N-terminal ectodomain can adopt multiple conformations.