Biomolecules for non-biological things: Peptide ‘Bundlemer’ design for model colloidal particle creation and interparticle lattice assembly

A solution-assembled system comprising computationally designed coiled coil bundle motifs, also known as 'bundlemers', will be discussed as model colloidal particle systems for the formation of hierarchical materials. The molecules are non-natural amino acid sequences and provide opportunities for controlled solution behavior and arbitrary nanostructure creation with peptides. With control of the display of the amino acid side chains (both natural and non-natural) throughout the peptide bundles, desired physical and covalent (through appropriate 'click' chemistry) interactions are designed to control interparticle interactions in solution, which involve both individual bundlemer particles as well as polymers of connected bundlemers. With proper design of individual bundlmer particles, porous lattices are formed through simply solution mixing. The lattices display crystalline-like structure but with regular pores on the nanoscale. The lattice structures are formed through two different assembly mechanisms. First, the functionalization of bundlemer paritcles with hydrophobic side chains on their exterior drive lattice formation through hydrophobic interactions. Second, lattices can be formed throught the complexation of oppositely charged bundlemer particles. Importantly in the second case, at least one of the particles in the oppositely charged pair must contain only one charge type (e.g., all positive charges or all negative charges). Since the peptides are computationally designed, it is possible to created folded particles with only one charge type. If both oppositely charged particles have mixed charges, as is typical in the vast majority of proteins, the particles form only amorphous aggregates and no lattice structure. Included in the discussion will be new, single charge peptide molecule design, hierarchical assembly pathway design through the mixing of oppositely charged coiled coil particles, control of nanostructure, and lattice characterization wtih cryotransmission electron micorscopy, transmission electron microscopy, small-angle x-ray scattering, and molecular dynamics simulations.