Elastin flexibility

Resilin and elastin, unlike other structural proteins, fulfill both definitions of an elastic material. Colloquially speaking, resilin and elastin are stretchy or flexible. They also fulfill the strict definition of an elastic material, i.e., the ability to deform in proportion to the magnitude of an applied stress without a loss of energy, and the recovery of the material to its original state when that stress is removed. Resilin and elastin are alone in the category of structural proteins (e.g., collagen, silk, etc.) in that they have the correct blend of physical properties that allow the proteins to fulfill both definitions of elasticity. Both proteins have high extensibility and combine that property with remarkable resilience [208]. 

Collagens (see p. 344), of which there are at least 19 different varieties, form fibers, fibrils, networks, and ligaments. Their characteristic properties are tensile strength and flexibility. Elastin is a fiber protein with a high degree of elasticity. 

A chain of repeated P bend motifs can form a flexible spring, a P spiral as proposed for elastin. Genes for spider silk have been cloned and are being used to engineer new proteins with commercial uses, e.g., to help anchor cells in regenerating body tissues. d/h/ ... 

Elastin is a macromolecule synthesized as a 70,000 single peptide chain, termed tropoelastin and secreted into the extracellular matrix where it is rapidly crosslinked to form mature elastin. The carboxy-terminal end of elastin is highly conserved with the sequence Gly-Gly-Ala-Cys-Leu-Gly-Leu-Ala-Cys-Gly-Arg-Lys-Arg-Lys. The two Cys residues that form disulfide crosslinks are found in this region as well as a positively charged pocket of residues that is believed to be the site of interaction with microfibrillar protein residues. Hydrophobic alanine-rich sequences are known to form a helices in elastin these sequences are found near lysine residues that form crosslinks between two or more chains. Alanine residues not adjacent to lysine residues found near proline and other bulky hydrophobic amino acids inhibit a helix formation. Additional evidence exists for (3 structures and 3 turns within elastin thereby giving an overall model of the molecule that contains helical stiff segments connected by flexible segments. 

The dermis is the largest layer of the skin. It is a region of strong and flexible connective tissue. The dermis consists of two primary layers, the papillary layer and the reticular layer. The papillary layer is the smallest layer of the dermis and is composed mainly of collagen and elastin fibers. The reticular layer is the largest layer of the dermis and is composed of mainly dense connective tissue. The layer of subcutaneous fat found directly beneath the dermis provides insulation and additional mechanical support to the skin. 

The polypeptide chain of elastin is rich in glycine, alanine, and valine and is very flexible and easily extended. In fact, its conformation probably approximates that of a random coil, with little secondary structure at all. However, the sequence also contains frequent lysine side chains, which can be involved in cross-links. These cross-links prevent the elastin fibers from being extended indefinitely, causing the fibers to snap back when tension is removed. The cross-links in elastin are rather different from those in collagen, for they are designed to hold several chains together. Four lysine side chains can be combined to yield a desmosine cross-link (see here)... 

The resilience of preconditioned SELP-47K fibres, either autoclaved or chemical cross-linked, approached that of native elastin, which is 90% [60], It is worth noticing that mechanical properties of SELP-47K fibres change dramatically between the dry state and the full hydrated state (Table 12.3). This is likely due to the plasticizing effect of water, which gives the silk-like blocks conformational flexibility by decreasing their crystallinity. 

Beneath the stratum corneum, the dermis (or corneum) is a tough supportive connective-tissue matrix, containing specialised structures and a substantial vascular supply. The dermis varies in thickness, being thin (0.6 mm) on the back of the eyelids and thicker (3 mm or more) on the back, palms and soles. The dermis provides flexibility and elasticity to the skin. Its major components are collagen, reticulin, elastin and fibres, and ground substance. The ground... 

Elastin is the protein found in elastic tissues such as tendons and arteries. The polypeptide chain of elastin is rich in alanine and glycine and is very flexible. It contains cross-links involving lysine side chains, which prevent the protein from extending excessively under tension and allow it to return to its normal length when tension is removed. 

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