Alpha-helical protein domains unify strength and robustness through hierarchical nanostructures.

Hierarchical nanostructures, ranging through atomistic, molecular and macroscopic scales, represent universal features of biological protein materials. Here we show for the case of alpha-helical (AH) protein domains that this use of molecular hierarchies within the structural arrangement leads to an extended physical dimension in the material design space that resolves the conflict between disparate material properties such as strength and robustness, a limitation faced by many synthetic materials. An optimal combination of redundancies at different hierarchical levels enables superior mechanical performance without additional material use. Our analysis is facilitated by the application of a Hierarchical Bell model (HBM), which explicitly considers the hierarchical architecture of H-bonds within the protein structure, providing a structure-property relationship of strength properties of AH protein nanostructures. The HBM is validated by large-scale molecular dynamics simulations of several model protein structures. Our findings may enable the development of self-assembled de novo bioinspired nanomaterials based on peptide and protein building blocks, and could help in elucidating the mechanistic role of AHs in cell signaling and mechanotransduction.