Design of Peptide Nanoparticles Using Simple Protein Oligomerization Domains

Viruses are naturally formed bionanoparticles ranging in size from about 20 to 150 nm. Remarkably, small viruses are composed of one single protein chain folding into a capsid structure with icosahedral symmetry. The icosahedron is built from 60 asymmetric units and is the largest closed shell in which every subunit is in an identical environment. It is characterized by 2-fold, 3-fold and 5-fold rotational symmetry axes. By superposition of different protein oligomerization domains onto the symmetry axes of an icosahedron, a nanoparticle with icosahedral symmetry can be designed. We have recently described such a design of peptide nanoparticles using coiled-coil protein oligomerization domains. Here we show that oligomerization motifs other than coiled-coils can be used to form nanoparticles by incorporating the globular foldon domain from fibritin with a trimeric beta -sheet conformation into the design. We expressed and purified 8 different peptides and performed refolding studies and biophysical characterization with analytical ultra centrifugation (AUC) and electron microscopy (EM). In the first design version we joined the foldon domain to the pentameric coiled-coil domain of COMP and varied the lengths of the linker sequences between the two domains. In this design we observed only smaller nanoparticles. When in the second design the foldon domain was extended with an additional trimeric coiled-coil domain as a combined trimerization domain that is linked to the COMP pentamer, we observed nanoparticles of sizes and molecular weights as would be expected for icosahedral symmetry. Viruses and virus-like particles (VLPs) are known for their ability to induce a strong humoral and hence antibody mediated immune response due to their repetitive antigen display. Peptide based nanoparticles have similar properties to VLPs, which are in clinical trials as a carrier in vaccination. Therefore, these peptide nanoparticles represent an alternative platform for subunit vaccine using the concept of repetitive antigen display.