Supramolecular Exchange among Assemblies of Opposite Charge Leads to Hierarchical Structures

Hierarchical assemblies of proteins into fibrillar structures occur in both physiologic and pathologic extracellular spaces and often involve interactions between oppositely charged peptide domains. However, the interplay between tertiary structure dynamics and quaternary hierarchical structure formation remains unclear. In this work, we investigate supramolecular mimics of these systems by mixing one-dimensional assemblies of small alkylated peptides bearing opposite charge and varying in peptide sequence. We found that assemblies with weak cohesive interactions readily create fibrous superstructures of bundled filaments as molecules redistribute upon mixing. Low cohesion allows molecules to escape from the original assemblies and exchange dynamics help them reassemble into electrostatically stable bundles. However, we also found that kinetic barriers can be encountered in these systems and limit formation of the hierarchical structures at pH values where charge densities are high. Increasing intermolecular cohesion using longer peptide sequences that form stable β-sheets was found to suppress superstructure formation. Our findings suggest that low internal cohesion in protein systems could facilitate the conformational rearrangements required to create hierarchical structures.