Subway Tile Self-assembly of Computationally Designed Peptides

Self-assembling peptides can form supramolecular coil-coiled motifs that provide a building block for hierarchical assembly. Previously, computationally designed, non-natural coiled coils, known as ‘bundlemers’, were designed with the same hydrophobic core and were composed of four identical peptides, each with four heptads. The resultant coiled coil particles were stable isotropic bundles with ~2 nm diameter and ~4 nm length. Herein, we introduce a novel design featuring a two-heptad offset within the four-heptad coiled-coil, which induces a staggered packing, mimicking a ‘subway-tile’ motif. This promotes physical polymerization and favors anisotropic interactions, which results in long 1D rods assembled through supramolecular interactions. This 1D rod physical polymerization was realized through an annealing process that allowed the coiled coils to overcome a kinetically trapped state and assemble into the designed rods. At higher concentrations these form hierarchical assemblies through electrostatic and methionine-mediated hydrophobic interactions. Two different sequences were characterized, each having a unique hierarchical assembled structure. One design led to the formation of tubes, while the second led to nanoporous lattice structures. Small-angle x-ray scattering, cryo-transmission and transmission electron microscopy, and atomic force microscopy collectively reveal aspects of the self-assembly pathway as well as the nanostructure formed during assembly.