Short Poster Lecture
In nature, coiled coil (CC) protein-folding motifs often occur in proteins with mechanical function, such as myosin or α-keratin. CCs consist of two to seven α-helices wound into a self-assembled superhelix. In the field of bioinspired materials, naturally occurring and synthetic CCs with high binding specificity have become versatile material building blocks, serving as reversible crosslink for hydrogels with applications in cell culture and tissue engineering. Despite their prevalence in natural and bioinspired materials, CC mechanical properties remain poorly understood. Yet, this information is critical for controlling and tuning the bulk properties of CC-based materials.
Towards the goal of generating mechanically tunable CCs and resulting CC-based materials, metal coordination sites were engineered into a well-characterized heterodimeric coiled coil (1). Protein-metal coordination bonds are strong, non-covalent interactions with self-healing properties mediated by amino acid ligands, such as histidine and cysteine. Here, two histidine residues were introduced into terminal helical turns with the goal of reversibly tuning their stability. Using atomic force microscopy-based single molecule force spectroscopy and circular dichroism spectroscopy, we demonstrate that histidine-metal coordination increases the stability of the CC mechanically and thermodynamically. We conclude that increasing the stability of single helical turns via metal binding directly affects the overall stability of the CC. Serving as crosslinks between branched poly(ethylene glycol) molecules, this histidine-modified CC is now being used for the development of self-healing biomimetic hydrogels. Oscillatory shear rheology reveals that the mechanical properties of these hydrogels can be reversibly tuned using transition metal ions and chelators. Our goal is to use these dynamic and tunable CC-crosslinked hydrogels as extra-cellular matrix mimics for investigating cellular mechanosensing.
1.Thomas, F., Boyle, A. L., Burton, A. J. & Woolfson, D. N., J. Am. Chem. Soc., 135 (2013) 5161.