Peptide Bundlemer Networks or Lattices: Controlling Cross-Linking and Self-Assembly Using Protein-like Display of Chemistry.

Coiled-coil 'bundlemer' peptides were selectively modified with allyloxycarbonyl (alloc)-protected lysine, a non-natural amino acid containing an alkene on its side chain. The specific display of this alkene from the coiled-coil surface with protein-like specificity enabled this residue to be used as a covalent linkage for creating peptide networks with controllable properties or as a physical linkage for the self-assembly of bundlemers into unexpected, intricate lattices driven by the hydrophobic nature of the side chain. For network formation, peptides were modified with both alloc-protected lysine and cysteine amino acids for solution assembly into solvent-swollen films and subsequent covalent cross-linking via thiol-ene photo click reactions. The degree of network cross-linking, as determined by rheometry, was finely tuned by varying the specific spatial display of reactive groups on the bundlemer building block particles, transitioning between intrabundle and interbundle cross-linking. The designed display of alloc groups from the center of the bundlemer building block also prompted particle self-assembly into an unexpected intricate lattice with a porous morphology. The lattices were studied in a variety of solution conditions using transmission electron microscopy, cryotransmission electron microscopy, and small-angle X-ray scattering. The approximate particle arrangement in the lattice was determined by using coarse-grained modeling and machine learning optimization techniques along with experimental methods. The proposed truss-like face-centered cubic packing of the alloc-functionalized bundlemers agrees well with the experimental results.