Resilin
It provides soft rubber-elasticity to mechanically active organs and tissue; for example, it enables insects of many species to jump or pivot their wings efficiently.
The elastic efficiency of the resilin isolated from locust tendon has been reported to be 97% (only 3% of stored energy is lost as heat).
It does not have any regular structure but its randomly coiled chains are crosslinked by di- and tri-tyrosine links at the right spacing to confer the elasticity needed to propel some jumping insects distances up to 38 times their length (as found in fleas).
After its discovery in elastic tendons in dragon flies and wing hinges in locusts, resilin has been found in many structures and organs in arthropods.
It is also abundant in the cuticle surrounding the abdomens of termites, ants, and bees, which expand and swell to a great extent during feeding and reproduction process.
[1] Amino acid composition in resilin was analyzed in 1961 by Bailey and Torkel Weis-Fogh when they observed samples of prealar arm and wing hinge ligaments of locusts.
The result indicates that resilin lacks methionine, hydroxyproline, and cysteine constituents in its amino acid composition.
Exon 3 encoded peptide takes on the unstructured form before loading, but transforms to an ordered beta-turn structure once stress is applied.
[4] It is proposed that as stress is applied, or there is energy input, exon 1 encoded peptide responds immediately due to its high flexibility.
The coexistence of PPII and beta-turn play an important role of increasing entropy as resilin returns to its disordered form.
[4] Andersen, in 1996, discovered that the tyrosine residues are involved in chemically covalent cross-links in many forms such as dityrosine, trityrosine, and tetratyrosine.
[1] Andersen came to this conclusion based on a study involving these two compounds in which he was able to rule out other forms of cross linking such as disulfide bridges, ester groups, and amide bonds.
[1] Though the mechanism of cross-linking of Tyrosine is understood that occurs through radical initiation, the cross linking of resilin still remains a mystery.
[4] The high concentration of proline and glycine, polyproline helices, and hydrophilic portions all serves to increase water content in resilin protein network.
[1] Rubber like proteins, such as resilin and elastin, are characterized based on their high resilience, low stiffness, and large strain.
Due to the remarkable rubber elasticity of resilin, scientists began exploring recombinant versions for a variety of material and medical applications.
With the rise in DNA technologies, this field of research has seen a rapid increase in the synthesis of biosynthetic protein polymers that can be tuned to having certain mechanical properties.
[12] During its study, pure resilin was synthesized into 20% protein-mass hydrogel and was cross-linked with ruthenium-catalyzed tyrosine in the presence of ultraviolet light.
[1] The results of these tests revealed that the resilience of both recombinant and native resilin were relatively similar but can differ in its applications.
Though this field of research is still ongoing, it has generated a wide amount of interest in the scientific community and is currently being investigated for a variety of biomedical applications in areas of tissue regeneration and repair.
Early work has focused on optimizing the mechanical properties, chemistry and cytocompability of these materials, but some in vivo testing of resilin hydrogels has also been performed.
