Covalent Stabilization of Collagen Mimetic Triple Helices and Assemblies by Dopa Crosslinking

Creating thermally stable collagen mimetic peptides (CMPs) is a persistent challenge. Nature leverages covalent crosslinkings to stabilize collagen's signature triple helical tertiary structure and higher-order assemblies. Herein, crosslinkings between levodopa (Dopa) and lysine can covalently stabilize the triple helix in CMPs is demonstrated. Since alkaline conditions catalyze the oxidation of the catechol on Dopa to a benzoquinone, while being in proximity to the nucleophilic lysine, it is hypothesized that this reaction can be a facile method to covalently capture the supramolecular structure of CMPs by simply increasing the pH of the aqueous solvent with the addition of sodium hydroxide. This covalent capture strategy successfully stabilizes CMP homotrimers and a de novo designed ABC-type heterotrimer demonstrating that the Lysine-Dopa covalent bond is best templated by a supramolecular, axial cation- $\pi$ pairwise interaction. In nature, collagen can hierarchically assemble into fibers. This behavior can be mimicked with the self-assembly of CMPs, but the resulting nanofibers typically exhibit thermal stability below body temperature. In a final application, Dopa-Lysine covalent capture also enhances the thermal stability of CMP nanofibers well above 37  $°$ C is demonstrated. This biomimetic covalent capture strategy can stabilize a wide variety of CMP systems and potentially enable the biomedical application of these materials.