Elastic proteins: biological roles and mechanical properties

Abstract

The term 'elastic protein' applies to many structural proteins with diverse functions and mechanical properties so there is room for confusion about its meaning. Elastic implies the property of elasticity, or the ability to deform reversibly without loss of energy; so elastic proteins should have high resilience. Another meaning for elastic is 'stretchy', or the ability to be deformed to large strains with little force. Thus, elastic proteins should have low stiffness. The combination of high resilience, large strains and low stiffness is characteristic of rubber-like proteins (e.g. resilin and elastin) that function in the storage of elastic-strain energy. Other elastic proteins play very different roles and have very different properties. Collagen fibres provide exceptional energy storage capacity but are not very stretchy. Mussel byssus threads and spider dragline silks are also elastic proteins because, in spite of their considerable strength and stiffness, they are remarkably stretchy. The combination of strength and extensibility, together with low resilience, gives these materials an impressive resistance to fracture (i.e. toughness), a property that allows mussels to survive crashing waves and spiders to build exquisite aerial filters. Given this range of properties and functions, it is probable that elastic proteins will provide a wealth of chemical structures and elastic mechanisms that can be exploited in novel structural materials through biotechnology.

Tissue elasticity and the ageing elastic fibre

“…1a). There is strong evidence supporting the hypothesis that elastin is both a highly compliant and a resilient protein (Gosline et al 2002). Gross mechanical testing studies on recombinant elastin membranes and rehydrated bovine nuchal ligaments, which had been subjected to repeated autoclaving to remove associated proteins, demonstrated that even small forces produce large extensions (Aaron and Gosline 1981), whilst stress-strain curves for extensions up to 50% demonstrated the ability of recombinant elastin peptides to recoil elastically (Keeley et al 2002).…”

“…Where a rod of length l 0 and cross-sectional area A is stretched to a length l by a force F, the elastic modulus (E) is calculated from the stress divided by the strain. The value of E relates to the biological function of a macromolecules; the elastic modulus of fibrillar collagen (1,200 MPa), for example, is relatively high reflecting the role of collagen fibrils in resisting tensile forces (Gosline et al 2002), in contrast E for elastin is low (1.1 MPa) (Aaron and Gosline 1981) and a small force will produce a large extension. The elastic modulus of fibrillin microfibrils, however, remains controversial with estimates ranging from 1.0 MPa (Aaron and Gosline 1981) to 96 MPa (Sherratt et al 2003) Gallagher et al 2005;Hubmacher et al 2006;Kielty et al 2002).…”

“…This tissue distribution, combined with the low modulus of elasticity and high resilience of elastin (Gosline et al 2002), allows elastic fibres to complement the tensile strength of fibrillar collagens (Kielty et al 2002). Elastic fibrerich dynamic tissues are therefore able to deform and store energy under normal physiological loads and to use this energy to drive recoil back to a resting state (Gosline et al 2002). The maintenance of these mechanical properties is central to the function of dynamic tissues within the cardio-respiratory system and it has been suggested that the age-related failure of elastic fibres may underpin the apparent 100-to 120-year limit on human life expectancy (Robert et al 2008) Although much progress has been made in recent years in defining elastic fibre composition, many questions remain as to the precise macro-molecular structure of fibrillin microfibrils and the functional roles played by distinct elastic fibre components in both mediating tissue elasticity and maintaining tissue homeostasis.…”

“…They are major components of the extracellular matrix (ECM) in dynamic tissues such as blood vessels (Davis 1993), skin (Braverman and Fonferko 1982) and the lungs (Pierce and Hocott 1960). This tissue distribution, combined with the low modulus of elasticity and high resilience of elastin (Gosline et al 2002), allows elastic fibres to complement the tensile strength of fibrillar collagens (Kielty et al 2002). Elastic fibrerich dynamic tissues are therefore able to deform and store energy under normal physiological loads and to use this energy to drive recoil back to a resting state (Gosline et al 2002).…”

On the Coupling Between the Incus and the Stapes in the Cat

“…The incudostapedial joint-capsule ligament has been found to consist mainly of elastin (Davies 1948;Harty 1953), rather than collagen as found in most joint capsules. The Young's modulus of elastin fibers from bovine ligament has been reported as 1.1 MPa (e.g., Gosline et al 2002). A value of 1 MPa has been adopted here for the joint capsule.…”