Design. An obvious model for a selfassembling protein particle is a viral capsid. The capsids of spherical viruses often have icosahedral symmetry, due to their need to build a large encapsulating structure from many copies of the same, or only few, capsid proteins. An icosahedron is the most efficient way to accomplish this. By utilizing pentameric and trimeric coiled coils, we have built a self-assembling nanoparticle which uses the threefold and fivefold symmetry of an icosahedrons [21] . The pentameric coiledcoil motif of the monomer is taken from Cartilage Oligomeric Matrix Protein (COMP) and the trimer is a de novo designed coiled coil. Self-assembly occurs when the coiled-coil domains of different monomers associate, forming the icosahedral nanoparticle ( Figure 1 ). A nanoparticle with this sort of architecture can then be used as a vaccine platform by extending the ends of the monomer with an epitope sequence. The Mono-M2e species of nanoparticle follows this plan ( Table 1) . As a result, it repetitively displays a monomeric form of M2e on the surface of the nanoparticles. The M2e peptide on the icosahedral nanoparticles lacks its C-terminal five residues to avoid problems with disulfide crosslinking that presumably require the native tetrameric conformation for proper formation. Although the simplest icosahedral particle with T1 icosahedral symmetry is made from 60 polypeptide chains, it may also be possible that Mono-M2e particles possess higher triangulation numbers, resulting in particles with an even greater molecular mass.