Elastic proteins possess rubber-like elasticity, in that they are capable of undergoing high deformation without rupture, storing the energy involved in deformation, and then returning to their original state when the stress is removed. The latter phase is passive (i.e., does not require an energy input), and the most efficient mechanisms return all (or nearly all) of the energy used in deformation. This latter requirement is not a prerequisite for elastomeric materials, as their biological requirements for energy storage/dissipation may be different.
The ability of proteins to exhibit rubber-like elasticity relates to their structure. Rubber-like materials must satisfy certain criteria: the individual components must be flexible and conformationally free, so that they can respond quickly to the applied stress, and they must be cross-linked to form a network, to distribute the stress throughout the system. These cross-links may be covalent or non-covalent, and examples of both types are found. Thus, the elastic properties of proteins are influenced by the nature of the elastomeric domains, their size, and the degree of cross-linking.
SEQUENCES OF ELASTOMERIC PROTEINS
Elastomeric proteins are widely distributed in the animal kingdom; however, only a few have been characterised in detail. This is due in part to their chemical/physical characteristics (non-globular nature, insolubility, cross-linking etc.) which make detailed characterisation difficult. More recently, gene sequences have become available, which have allowed sequence comparisons to be made and structure–function relationships to be studied.