Proteins elastin

The fibrous protein elastin found extensively in connective tissues is unlike collagen in that it occurs in a less well ordered fashion, furthermore, there are quite marked differences seen between the chemical compositions of collagen and elastin. Whereas collagen comprises a very limited number of different amino acids, elastin contains a wider variety, the most abundant being glycine (approximately 30% dry weight), alanine (23%) valine (15%) and proline (12%). 

Many tissues, such as lung, blood vessels, and skin, require elasticity for proper function this property is fulfilled by the matrix elastic fibers, which are composed of the proteins elastin and fibrillin. 

In addition to the 20 common amino acids, proteins may contain residues created by modification of common residues already incorporated into a polypeptide (Fig. 3-8a). Among these uncommon amino acids are 4-hydroxyproline, a derivative of proline, and 5-hydroxylysine, derived from lysine. The former is found in plant cell wall proteins, and both are found in collagen, a fibrous protein of connective tissues. 6-N-Methyllysine is a constituent of myosin, a contractile protein of muscle. Another important uncommon amino acid is y-carboxyglutamate, found in the bloodclotting protein prothrombin and in certain other proteins that bind Ca2+ as part of their biological function. More complex is desmosine, a derivative of four Lys residues, which is found in the fibrous protein elastin. 

Copper was recognized as nutritionally essential by 1924 and has since been found to function in many cellular proteins.470-474 Copper is so broadly distributed in foods that a deficiency has only rarely been observed in humans.4743 However, animals may sometimes receive inadequate amounts because absorption of Cu2+ is antagonized by Zn2+ and because copper may be tied up by molybdate as an inert complex. There are copper-deficient desert areas of Australia where neither plants nor animals survive. Copper-deficient animals have bone defects, hair color is lacking, and hemoglobin synthesis is impaired. Cytochrome oxidase activity is low. The protein elastin of arterial walls is poorly crosslinked and the arteries are weak. Genetic defects in copper metabolism can have similar effects. 

The protein elastin presents another opportunity to create amyloid-like fibrils from natural proteins for the purpose of developing biomaterials. Elastin is found in tissue where it imparts elastic recoil, and fibrils formed from this protein may demonstrate some of the elastic properties of the constituent elastic proteins (Bochicchio et al., 2007). Elastin typically contains the sequence poly(ZaaGlyGlyYaaGly) (where Zaa, Yaa = Val or Leu) (Tamburro et al., 2005), and short stretches of the protein retain the ability to form structures similar to the original protein. Simple proline to glycine mutations in the hydrophobic domains of elastin can induce the formation of amyloid-like fibrils (Miao et al., 2003), suggesting that fibrillar materials can be easily generated from these sequences. 

We now well appreciate, of course, that polymers are virtually everywhere. Some of them occur naturally, and we continue to better understand their compositions, structures, and properties. Many of these materials have been used since the dawn of human existence, for food, obviously. Cellulose alone has been essential for clothing, fire, shelter, tools, weapons, writing, and art. Leather is probably the result of the first synthetic polymer reaction, essentially the crosslinking of protein (elastin). How we progressed over time to the Polymer Age is a fascinating series of stories, some of which are well worth recounting here. 

Some tissues, such as ligaments and arterial blood vessels, need highly elastic fibers. Such tissues contain large amounts of the fibrous protein elastin. 

The media represents the major portion of the vessel wall and provides most of the mechanical strength necessary to sustain structural integrity. The media is organized into alternating layers of interconnected smooth muscle cells and elastic lamellae. There is evidence of coUagen throughout the media. These small collagen fibers are found within the bands of smooth muscle and may participate in the transfer of forces between the smooth muscle cells and the elastic lamellae. The elastic lamellae are composed principally of the fiberous protein elastin. The number of elastic lamellae depends upon the wall thickness and the anatomical location [12]. In the case of the canine carotid, the elastic lamellae account for a major component of the static structural response of the blood vessel [13]. This response is modulated... 

D.W. Urry, C.-H. Luan, R.D. Harris, and K.U. Prasad, Aqueous Interfacial Driving Forces in the Folding and Assembly of Protein (Elastin)-Based Polymers Differential Scanning Calorimetry Studies. Polym. Preprints, Div. Polym. Chem., Am. Chem. Soc.,21,188-189,1990. 

Elastase is a serine protease that is a protein target for drugs used in the treatment of emphysema. Elastase is so named because it rapidly hydrolyzes the otherwise nearly indigestible protein elastin, which is rich in Ala, Gly, and VaL Elastase specifically cleaves peptide bonds following small nonpolar residues, particularly Ala. 

Monte Carlo simulations have been used to calculate thermo-elastic results through the temperature coefficient of the unperturbed dimensions. In the case of networks of the protein elastin, such results were used to evaluate alternative theories for the molecular deformation mechanism for this bioelastomer. ... 

ELRs are a promising model of biocompatible protein-based polymers. The basic structure of ELRs involves a repeating sequence based on the recurring sequences found in the mammalian elastic protein elastin [4]. As far as their properties are concerned, some of their main characteristics are derived from those of the natural protein. Elastin is an extracellular matrix protein that is present in aU vertebrate connective tissue. Its functions include the provision of elasticity and resilience to tissues, such as large elastic blood vessels (aorta), elastic ligaments, lung and skin, which are subjected to repetitive and reversible deformation [5, 6]. 

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