Elastomeric proteins

There are several excellent reviews and a comprehensive book dealing with the stmcture and properties of elastomeric proteins, and readers are urged to consult these references for a more detailed background to the field [9,13,14]. 

Shewry, P.R., Tatham, A.S., and Bailey, A.J. (Eds.), Elastomeric Proteins Structures, Biomechanical Properties and Biological Roles, Cambridge University Press, Cambridge, 2002. 

Tatham, A.S. and Shewry, P.R., Elastomeric proteins Biological roles, struemres and mechanisms. Trends Biochem. Set, 25(11), 567-571, 2000. 

Elastomeric polypeptides are a class of very interesting biopolymers and are characterized by mbber-like elasticity, large extensibility before rupture, reversible deformation without loss of energy, and high resilience upon stretching. Their useful properties have motivated their use in a wide variety of materials and biological applications. Here, we focus on two elastomeric proteins and the recombinant polypeptides derived thereof. 

The first elastomeric protein is elastin, this structural protein is one of the main components of the extracellular matrix, which provides stmctural integrity to the tissues and organs of the body. This highly crosslinked and therefore insoluble protein is the essential element of elastic fibers, which induce elasticity to tissue of lung, skin, and arteries. In these fibers, elastin forms the internal core, which is interspersed with microfibrils [1,2]. Not only this biopolymer but also its precursor material, tropoelastin, have inspired materials scientists for many years. The most interesting characteristic of the precursor is its ability to self-assemble under physiological conditions, thereby demonstrating a lower critical solution temperature (LCST) behavior. This specific property has led to the development of a new class of synthetic polypeptides that mimic elastin in its composition and are therefore also known as elastin-like polypeptides (ELPs). 

Andersen SO (2003) In Shewry PR, Tatham AS, Bailey AJ (eds) Elastomeric proteins structures, biomechanical properties, and biological roles. Cambridge University Press, Cambridge, pp 259-278... 

The tenet of classical rubber theory has been that the chains are in random networks and the networks comprise a Gaussian distribution of end-to-end chain lengths. However, the mechanisms and molecular bases for the elasticity of proteins are more complex than that of natural rubber. In biological systems elastomeric proteins consist of domains with blocks of repeated sequences that imply the formation of regular stmctures and domains where covalent or noncovalent cross-linking occurs. Although characterised elastomeric proteins differ considerably in their precise amino acid sequences they all contain elastomeric domains comprised of repeated sequences. It has also been suggested that several of these proteins contain p-tums as a structural motif (Tatham and Shewry 2000). 

Elastomeric Proteins Structures, Biomechanical Properties and Biological Roles. 

Table 2 Material properties of natural elastomeric proteins ...

As described above for elastin and resilin, the ability of elastomeric proteins to exhibit elasticity relies on the molecular movement, stmctural folding, and conformational freedom of individual components so that they can instantaneously respond to the applied force within a cross-linked network to distribute the stress throughout the system. Stretching initially will interrupt interactions between the loops such as hydrophobic interactions, hydrogen bonding, and electrostatic interactions, while at higher extensions a decrease in conformational entropy will be prevalent. To date, different models are proposed to explain the mechanisms of elasticity for resilin, based on the knowledge from elasticity models that have been proposed for elastin. 

As shown in Table 3, in aqueous solution these short resilin-like peptides adopt a mixture of PPII stmcture, unordered conformations, and p-tums, while in Ttifluoroethanol (TFE) primarily type-11 p tums populate the conformational space. These findings are consistent with what Andersen has predicted and are also very similar to other elastomeric proteins studied. Interestingly, coacervation, a common phenomenon in elastin and abductin (in which a protein-rich phase is formed when the temperature is raised), has not been observed in resilin-like polypeptides (RLPs). This is almost certainly due to the inaeased hydrophilicity of resilin, which is soluble in water under all relevant experimental conditions. As mentioned above, additional spectroscopic studies on extended RLPs, as well as manipulations of RLP sequences via the introduction of different amino acid analogs and evaluation of corresponding conformational changes, would be useful to elucidate the mechanism of elasticity of resilin. 

D.W. Urry,T. Hugel, M. Seitz, H. Gaub, L. Sheiba, J. Dea, J. Xu, L. Hayes, F. Prochazka, and T. Parker, Ideal Protein Elasticity The Elastin Model. In Elastomeric Proteins Structures, Biomechanical Properties and Biological Roles P.R. Shewry, A.S. Tatham, and A.J. Bailey, Eds. Cambridge University Press, The Royal Society Chapter Four, pages 54-93,2003. 

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