Coiled coil peptide 'bundlemers': model nanoparticles for electrostatically-driven interparticle assembly

Computationally designed peptide coiled coils, also named "bundlemers", provide unique opportunities to exactly specify the display of exterior surface amino acid side chains thus offering direct, local control of electrostatic interactions between bundlemers in solution. In this study, highly ordered nanostructures were observed in the presence of particular multivalent couterions in solutions of specifically charged bundlemers. The solutions and final assemblies were characterized by small-angle scattering methods and transmission electron microscopy, respectively. Distinctive assembly morphologies were achieved by various counterions such as multivalent molecular ions, polyelectrolytes, and biomolecules. More importantly, the impact of peptide sequence, and the inherent surface charge anisotropy and patterning, was investigated owing to the inherent programmability of computational design. Two categories of bundlemers were studied: Bundlemers with only positively charged residues ('single-charged' bundlemers) and bundlemers with both positively and negatively charged residues ('mix-charged' bundlemers). Single-charged bundlemers revealed a selection of counterions that induced colloidal crystal-like structures while mix-charged bundlemers formed amorphous aggregates in solution.