On the other hand, the native conformation of M2 is a tetramer. Hence, to elicit conformationally specific antibodies, the M2e antigen displayed by a vaccine particle should ideally be tetrameric. With that in mind, we designed the Tetra-M2e peptide ( Table 1) . Instead of a pentameric coiled coil, this polypeptide uses the tetrameric coiledcoil motif from the protein tetrabrachion [29] . Self-assembly using this peptide would result in a nanoparticle with threefold and fourfold symmetry axes or octahedral symmetry. As opposed to the larger icosahedral Mono-M2e, this octahedral particle would only have 24 polypeptide chains. In addition, the epitope is now constrained to its native tetrameric conformation. The full-length M2e contains two cysteine residues. The formation of disulfide bridges between the cysteines of adjacent chains under oxidizing conditions is thought to stabilize their tetrameric conformation. The speed and ease of protein expression and purification, as well as of the self-assembly process, contribute to the overall viability of this technology as a vaccine platform. To facilitate purification, we have included polyhistidine tags at the N-terminal ends of the peptides.