A secondary structure within small peptides guiding spontaneous self-aggregation and nanoparticle formation

Polyhedrin from <i>Autographa californica</i> baculovirus is a protein that self-aggregates forming a crystal structure known as polyhedra. Baculovirus occluded inside the crystal withstand for years at room temperature retaining infectivity. By investigating the smallest fragment from polyhedrin retaining the self-aggregation properties we identified a 29 amino acid sequence that spontaneously forms nanoparticles. This small sequence contains a β-sheet followed by an α-helix. We synthesized a variety of peptides with different amino acid sequences but similar secondary structure and discovered that the peptides self-aggregate forming nanoparticles of different geometries and sizes. Furthermore, peptides containing only the β-sheet or the α-helix aggregate also. This study led to the discovery of secondary structures that spontaneously self-aggregate forming nanoparticles even when fused to the green fluorescent protein.