Side-Chain Chemistry Governs Hierarchical Order of Charge-Complementary -sheet Peptide Coassemblies

Self-assembly of proteinaceous biomolecules into functional materials with ordered structures that span length scales is common in nature yet remains a challenge with designer peptides under ambient conditions. This report demonstrates how charged side-chain chemistry affects the hierarchical co-assembly of a family of charge-complementary beta-sheet-forming peptide pairs known as CATCH(X+/Y-) at physiologic pH and ionic strength in water. In a concentration-dependent manner, the CATCH(6K+) (Ac-KQKFKFKFKQK-Am) and CATCH(6D-) (Ac-DQDFDFDFDQD-Am) pair formed either beta-sheet-rich microspheres or beta-sheet-rich gels with a micron-scale plate-like morphology, which were not observed with other CATCH(X+/Y-) pairs. This hierarchical order was disrupted by replacing D with E, which increased fibril twisting. Replacing K with R, or mutating the N- and C-terminal amino acids in CATCH(6K+) and CATCH(6D-) to Qs, increased observed co-assembly kinetics, which also disrupted hierarchical order. Due to the ambient assembly conditions, active CATCH(6K+)-green fluorescent protein fusions could be incorporated into the beta-sheet plates and microspheres formed by the CATCH(6K+/6D-) pair, demonstrating the potential to endow functionality. Co-assembly of charge-complementary peptides affords opportunities to create fibrillar biomaterials with molecular-level features that cannot be achieved in single-component systems. However, our ability to predict fibrillar network architecture based on peptide pair sequence characteristics is lacking. This report shows how the type of charged amino acid affects supramolecular organization in charge-complementary beta-sheet peptide co-assemblies.+image