Mechanical tunability of biological materials via protein-metal cross-linking

• Applicant: Professor Dr. Matthew Harrington
• Subject Area: Synthesis and Properties of Functional Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 246897665

• Final Report Year: 2019

Final Report Abstract

Metal coordination interactions play important roles in the mechanical performance of certain protein-based biological materials, most prominently the mussel byssus. Specifically, amino acids including histidine and DOPA coordinate with transition metal ions (e.g. Fe, V, Cu and Zn) to provide exceptional toughness and even self-healing behavior. While the mechanisms underlying this mechanical enhancement are only partially understood, researchers have adapted these principles into bio-inspired metallopolymers. In the initial proposal, we aimed to bioengineer metal-binding histidine amino acid residues into the primary sequence of a rubbery protein biopolymer known as resilin with the intention of modulating the mechanical properties via metal coordination. At the outset of the project, it was established that resilin could be recombinantly expressed and photo-crosslinked into soft elastic biopolymer. We recombinantly altered the resilin motif to contain two His residues. Using vibrational spectroscopy, we confirmed the modified protein coordinated metal ions, which resulted in a nearly 100-fold increase in stiffness compared with wild-type resilin. However, a deeper analysis of the structure-function relationship defining this material was not possible due to the low yield of material. Thus, in line with the overarching goals of the project, we instead harnessed polymer-peptide hybrid molecules with synthetic peptides based on histidine-rich metal binding sequences from the mussel byssus. It was found that the hybrid molecules formed hydrogels mediated via histidine, even in the absence of metal ions, but that addition of metal ions could further modulate hydrogel mechanics. Furthermore, to dig deeper into the role of self-assembly in determining the material properties of natural metallpolymeric materials, we investigated mussel byssus assembly using a combination of histology and confocal Raman spectroscopy. This study provided new insights into this process including the prominent role of smectic liquid crystalline proteins and into the role of metals in self-assembly. These insights have relevance in the fields of tissue engineering and in the sustainable fabrication of polymeric materials, and have provided further impetus for the current work in our group.

Publications

• (2015) Recombinant engineering of reversible cross-links into a resilient biopolymer. Polymer 69, 255- 263
  Degtyar, E., Mlynarczyk, B., Fratzl, P. and Harrington, M.J.
  
• (2017) Rapid self-assembly of complex biomolecular architectures during mussel byssus bio-fabrication. Nature Communications. 8, 14539
  Priemel, T., Degtyar, E., Dean, M.N., Harrington, M.J.
  
• (2018) Exploring mussel byssus fabrication with peptide-poiymer hybrids: Role of pH and metal coordination in self-assembly and mechanics of histidine-rich domains. European Polymer Journal. 109, 229-236
  Trapaidze, A., D’Antuono, M., Fratzl, P., Harrington, M.J.