Fibrous proteins elastic fibers

From the foregoing sections of this review we may conclude that the elastic fibers of yellow connective tissue are composed in the main of a protein which is characteristic of this type of tissue and which is quite distinct from collagen or other fibrous proteins. Elastic fibers have characteristic staining properties, but they vary in thickness and morphological... 

Microfibrillar protein Protein Amino acids Fibrous core of elastic fibers... 

The physiology and morphology of the fibrous components of connective tissue has been reviewed recently by Hall (1959) with special reference to the elastic fiber and its relationship to collagen, in the present review the intention is to bring together recent information on the chemical nature of elastic fibers, and the chemistry of elastin as a protein. 

Elastin - Elastin is a highly elastic fiber present in ligaments and arterial blood vessels. The polypeptide is rich in glycine, alanine, and valine. Its secondary structure is the most random of the fibrous proteins described here. Like collagen, elastin contains lysine groups involved in cross-links between the chains. In elastin, however, four lysine chains can be combined to form a desmosine cross-link (see here). Thus, fewer cross-links are needed to provide strength for the chains and a more elastic network is created. 

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

Proteins can be classified by the functions just discussed. They can also be classified into two major types, fibrous and globular, on the basis of their structural shape. Fibrous proteins are made up of long rod-shaped or stringlike molecules that can intertwine with one another and form strong fibers. They are water-insoluble and are usually found as major components of connective tissue, elastic tissue, hair, and skin. Examples are collagen, elastin, and keratin (see > Figure 9.4). 

As Monod states in his treatise. On Symmetry and Function in Biological Systems, One may set aside the simple problem of fibrous proteins. Being used as scaffolding, shrouds or halyards, they fulfill these requirements by adopting relatively simple types of translational symmetries. Therefore, it was not anticipated that positive cooperativity, the effect Monod thought to be the second secret of life, second only to the structure of DNA, would be most beautifully demonstrated by designed variations of a repeating sequence of the mammalian elastic fiber based on translational symmetry. 

Based on a series of designed elastic-contractile model proteins. Figure 1.2 exhibits a family of curves whereby stepwise linear increases in oil-like character give rise to supra-linear increases in curve steepness, that is, in positive cooperativity. More oil-like phenylalanine (Phe, F) residues with the side chain -CH2-C6H5 replace less oil-like valine (Val, V) residues with the side chain -CH-(CH3)2. Here the structural symmetry is translational with as many as 42 repeats (Model protein v) of the basic 30-residue sequence, and the structure is designed beginning with a repeating five-residue sequence of a fibrous protein, the mam-mahan elastic fiber. 

The a-helix is found in fibrous proteins such as wood, hair, and fingernails. These fibers are slightly elastic stretching a hair, for example, will stretch the hydrogen bonds but will not break the amide bonds. 

Measurement of mechanical properties of proteins, especially those of fibrous proteins, has been an important interdisciplinary concern in the history of protein science. In fact, the very early X-ray work by Astbury and his colleagues established the force dependent conformational transition of keratin fiber between a- and /3-forms [15]. A large body of work has since been accumulated on the measurement of mechanical parameters of fibrous structures made of keratin, collagen, dentin and other structural proteins [10, 14, 16, 17]. Measurement was done at the macroscopic level on higher order assemblies of fibrous proteins, applying established methods in materials science for the determination of, for example, static and/or dynamic elastic modulus [14],... 

Biomechanical Machines. The mechanical properties of fibrous polypeptides could be put to use for the commercial production of fibers (qv) that are more elastic and resiUent than available synthetics (see Silk). The biochemical properties of proteins could also be harnessed for the conversion of mechanical energy to chemical energy (35). 

Partial hydrolysis of elastin by reagents other than organic acids also gives rise to a mixture of soluble proteins similar to a- and /3-elastin. Thus Wood (quoted by Hall et al, 1952) first demonstrated that partial hydrolysis with dilute sodium hydroxide yields a protein which forms a reversible coacervate on raising the temperature of its solutions. Later Wood (1958) showed that on prolonged heating in aqueous solution a-elastin is converted into an insoluble gellike form. Reconstituted fibers of heat-treated a-elastin resembled fibrous elastin in their elastic behavior and X-ray-dif-fraction pattern but imlike purified elastin they were dissolved by 1 % acetic acid at 100°C and by crystalline trypsin. 

It is probable that Bailey s first interest in the muscle field, in which lies his greatest contribution, was aroused by the work of Astbury and Dickinson who showed that fibers of denatured myosin behaved in ways similar to keratin so far as their elastic properties were concerned and their structures were revealed by X-ray analysis. At this time the Chibnall group was much interested in the amino acid composition of proteins. The obvious similarities in fibrous behavior between keratin and myosin despite their differences in amino acid composition, particularly in cystine content, stimulated Bailey to make a comparative study of the composition of some of the then recognized muscle proteins. This was Bailey s first paper on muscle and extension of the... 

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