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Development of Self-assembled Protein-based Nanostructured Materials With Tailored Mechanical Properties

The main goal of this research is to develop novel soft materials with unusual and programmable mechanical and viscoelastic properties, which will self-assemble from protein-based building blocks, and to understand the principles that relate the properties of these materials to the properties of their protein building blocks. The unusual properties of these materials will be a) extremely large stretch ratios of around 1000% and b) programmable ratios of the storage modulus to the loss modulus. Large stretch ratios will be achieved by exploiting proteins whose folded length is on the order of 1/10th of the length of the polypeptide chain. Storage and loss moduli will be controlled by varying the percentage of protein domains that mechanically unfold and refold in near equilibrium, with minimal energy dissipation, such as ankyrin repeats (ANK)1,2, (Fig. 1) and mechanically strong protein domains that dissipate large amounts of energy when mechanically unfolded, such as immunoglobulin (Ig) domains (Fig. 1). Self-assembly of these protein building blocks into materials will be achieved by exploiting two novel approaches: a) using functionalized homo tetrameric proteins to serve as network nodes and b) using the newly-developed SpyTag-SpyCatcher technology3 to covalently connect protein building blocks to tetrameric hubs4. At low forces (up to ~100 pN/molecule) these materials should will display large stretch ratios and will stretch in a fully reversible fashion with minimal energy dissipation. At higher forces (>100 pN/molecule) these materials will display significant plasticity and will dissipate great amounts of energy, working as shock absorbers(Fig. 1)

Fig. 1. A schematic of self-assembly of protein building blocks into a soft material with tailored viscoelastic properties. A. AFM stretching of protein building blocks crosslinked through a tetrameric proteins. B. Self-assembled 2D matrix composed of ankyrin repeats and immunoglobulin domains. C) Force-extension profile of an ANK-Ig hybrid protein. The area hhighlighted in yellow represents the energy dissipated during unfolding of Ig domains.

Key References

  1. Lee, G. et al. Nanospring behaviour of ankyrin repeats. Nature 440, 246-9 (2006).
  2. Lee, W. et al. Full Reconstruction of a Vectorial Protein Folding Pathway by Atomic Force Microscopy and Molecular Dynamics Simulations. Journal of Biological Chemistry 285, 38167-38172 (2010).
  3. Zakeri, B. et al. Peptide tag forming a rapid covalent bond to a protein, through engineering a bacterial adhesin. Proceedings of the National Academy of Sciences 109, E690-E697 (2012).
  4. Kim, M. et al. Nanomechanics of Streptavidin Hubs for Molecular Materials. Advanced Materials 23, 5684-5688 (2011).