Hybrid hydrogels cross-linked by genetically engineered coiled-coil block proteins.

Hybrid hydrogels of hydrophilic synthetic polymers cross-linked by protein modules undergo externally triggered volume transitions as a result of protein conformational changes. To investigate the influence of coiled-coil protein structure and stability on hydrogel volume transition, a series of block proteins containing interspersed naturally derived recombinant coiled-coils was synthesized. Proteins were characterized using circular dichroism, size exclusion chromatography, gel electrophoresis, and analytical ultracentrifugation. The block proteins formed self-associating oligomers and displayed thermal unfolding profiles indicative of a hierarchic higher-order structure. Hybrid hydrogels were assembled from an N-(2-hydroxypropyl)-methacrylamide (HPMA) copolymer and His-tagged block proteins through metal complexation. A temperature-induced decrease in hydrogel swelling was observed, and the onset temperature of the volume transition corresponded to the onset temperature of protein unfolding. We conclude that stimuli-responsive properties of hybrid hydrogels can be tailored by engineering the structure and properties of protein cross-links.