Chapter 2. Native Resilin: Properties, Occurrence and Biological Functions of a Remarkable Bio-elastomer

Resilin is an elastomeric protein that occurs in arthropod exoskeletons and stands out for its almost perfect resilience of 92–97%, the reason why it is often called a rubber-like protein. It consists of long, randomly oriented proline- and glycine-rich polypeptide chains of high mobility and little secondary structure, which are covalently linked by dityrosine and trityrosine cross-links. This structure endows resilin with a low stiffness, high long-range deformability, and outstanding resilience. Resilin often forms composites with chitin via its chitin-binding domain and with other proteins. Based on the amount and purity of resilin, the direction of the embedded chitin fibres, the specific structure of resilin's polypeptide chains, and the ratio of di- and trityrosine cross-links, resilin shows divergent mechanical responses to different directions and types of applied force. So far, resilin has been found in various exoskeleton systems, including leg and wing joints, vein joints and membrane areas, tarsal setae, tendons, sensory organs, and specialised structures like food-pumps, sound production organs, extensible abdominal cuticles, and transparent optical elements. Amongst others, resilin serves the generation of deformability and flexibility, the elastic energy storage, the adaptability to uneven surfaces in contact, and the reduction of material fatigue in these exoskeleton systems.