Fibrous proteins ELASTIN Major fibrous protein of epithelial tissues is a keratin Major fibrous proteins of connective tissue are: Collagen and Elastin •Much or most of the polypeptide chain is parallel to a single axis •Fibrous proteins are often mechanically strong & highly cross-linked •Fibrous proteins are usually insoluble •Usually play a structural role ELASTIN It is a connective tissue protein that is responsible for properties of extensibiity and elastic recoil in tissues. Although not as widespread as collagen, elastin is present in large amounts, particularly in tissues that require these physical properties e.g. lung, blood vessels and elastic ligaments and small amounts in ear and skin. In contrast to collagen, which forms fibers that are tough and have high tensile strength, elastin is a connective tissue protein with rubber-like properties. Elastic fibers are composed of elastin and glycoprotein microfibrils and are found in the lungs, the walls of large arteries, and elastic ligaments. They can be stretched to several times their normal length, but recoil to their original shape when the stretching force is relaxed. STRUCTURE OF ELASTIN Elastin is an insoluble protein polymer synthesized from a precursor, TROPOELASTIN, which is a linear polypeptide composed of about 700 amino acids that are primarily small and nonpolar (for example, glycine, alanine, and valine). Tropoelastin is secreted by the cell into the extracellular space. There it interacts with specific glycoprotein microfibrils, such as FIBRILLIN, which function as a scaffold onto which tropoelastin is deposited. Elastin is also rich in proline and lysine, but contains only a little hydroxyproline and hydroxylysine. Some of the lysyl side chains of the tropoelastin polypeptides are oxidatively deaminated by lysyl oxidase, forming allysine residues. Three of the allysyl side chains plus one unaltered lysyl side chain from the same or neighboring polypeptides form a desmosine cross-link .THIS PRODUCES ELASTIN— an extensively interconnected, rubbery network that can stretch and bend in any direction when stressed, giving connective tissue elasticity Elastin fibers in relaxed and stretched conformations. DYNAMIC STRUCTURE OF ELASTIN: The structure of elastin is called a b spiral, and is loosely held together by the hydrophobic force. It is easily deformed to an extended configuration, but will relax back to a compact conformation. Repeating unit: PGVGV ELASTIC FIBERS. These scanning electron micrographs show (A) a lowpower view of a segment of a dog's aorta and (B) a high-power view of the dense network of longitudinally oriented elastic fibers in the outer layer of the same blood vessel. All the other components have been digested away with enzymes and formic acid. FIBRILLIN . A large glycoprotein (about 350 KDa) that is a structural component of microfibrils 10-12 nm fibers found in many tissues. It is secreted into ECM by fibroblast and becomes incorporated into the insoluble microfibrils which appear to provide a scaffold for deposition of elastin. . MARFAN SYNDROME. It is a relatively prevalent inherited disease affecting connective tissues. It is inherited as an autosomal dominant trait. It affects the eyes, the skeletal system and hyper-extensibility of the joints and cardiovascular system. This syndrome is due to mutations in the gene for fibrilin. With this disease, abnormal fibrillin protein is incorporated into microfibrils along with normal fibrillin, inhibiting the formation of functional microfibrils. [Note: Patients with OI, EDS, or Marfan syndrome may have blue sclera due to tissue thinning that allows underlying pigment to show through.] Deletion of elastin gene have been found in 90% of the subjects with Williams syndrome, a developmental disorder affecting connective tissue and the central nervous system. A number of skin diseases are associated with accumulation of elastin. Alternatively, a decrease of elastin is found in – conditions such as pulmonary emphysema and aging of the skin Genetic defects in elastin underlie Williams Syndrome Facial features associated with Williams Syndrome Dental features include small widely spaced teeth and malocclusion.