BPS2026 – Conformational analysis of the N-terminal ectodomain of membrane-bound influenza A M2 protein in complex with an antibody

The N-terminal ectodomain of influenza A M2 protein exhibits high sequence conservation across strains and is a target for universal influenza vaccine development. M2 is a 97-amino-acid membrane-bound protein that consists of an N-terminal ectodomain (M2e, residues 1-21), a transmembrane domain (residues 22-47), and a C-terminal cytoplasmic domain (residues 47-97). Despite its significance, many structural studies of the M2 protein have not included M2e in their analyses. The therapeutic potential of monoclonal antibodies against M2e has been explored; yet, there is limited atomic level detail on M2e-antibody complexes. Our work uses full-length M2 protein embedded in lipid bilayer membrane nanodiscs both with and without antibody present. Characterization methods include size-exclusion chromatography, dynamic light scattering, biolayer interferometry, and electron microscopy. Using site-directed spin labeling electron paramagnetic resonance spectroscopy we examined the conformation, dynamics, and membrane topology of sites along M2e. Results are consistent with a region that can adopt multiple conformations, including a population that has a turn in the middle of the ectodomain whose proximity to the membrane surface is sensitive to membrane composition.