(357an) Design Parameters for Water-Responsive Protein Block Copolymers

Natural water-responsive (WR) biological materials are abundant, having independently evolved in places such as wheat awns, pinecones, and bacterial spores. Water-responsive biomaterials are of interest for applications as high-energy actuators, which can be useful in soft robotics or for capturing energy from natural fluctuations in humidity. Recent work on water responsive protein materials has shown that β-sheet structure correlates with WR energy density, but the design parameters for water response in proteins remain poorly understood. Here we design, synthesize, and study protein block-copolymers consisting of two α-helical domains derived from cartilage oligomeric matrix protein coiled-coil (C) flanking an elastin-like peptide domain (E). We use these protein materials to create water-responsive actuators whose energy densities outperform mammalian muscle by two orders of magnitude and match reported spider silk actuators, the highest found in nature. To elucidate the effect of structure on water response, CEC was compared to a variant, CEC_L44A, in which the Leu at position 44 in each C domain was mutated to Ala, abolishing any α-helical structure and providing an unstructured control material. In this work, we study the relationship between protein secondary structure, higher-order protein assemblies, and WR energy density in order to develop design parameters for water-responsive biomaterials.