Elastin

Elastin is a fibrillar, elastic structural protein closely related to collagen that is found in most vertebrates.

Elastin is the main component of the elastic fibers in connective tissue. Elastin consists of long, coiled polypeptide chains cross-linked by desmosin .  This network structure accounts for the elasticity of the structural protein. Its building blocks are primarily glycine, alanine, valine, proline, leucine, and isoleucine. They are present in the repeating subsequences Gly-Gly-Val-Pro and Gly-Val-Pro-Gly.  In vertebrates, elastin is found primarily in organs where elastic properties are of great functional importance, such as the lungs, skin, and blood vessels.  In particular, elastin in elastic fibers ensures the elasticity of large blood vessels (e.g., the aorta). 

Elastin is secreted by fibroblasts in a soluble, uncross-linked form (tropoelastin) and is subsequently cross-linked by the enzyme lysyl oxidase (LOX). The amino acid lysine is responsible for this cross-linking.

Copper deficiency and mutations in the LOX gene (the LOX gene, located on chromosome 5 at the q23.3-q31.2 locus, encodes lysyl oxidase) can lead to reduced lysyl oxidase enzyme activity and cutis laxa.

Mutations in the elastin gene (chromosome 7q11.23) cause abnormalities in elastin. The associated clinical presentations include autosomal dominant cutis laxa (ADCL) and supravalvular aortic stenosis (SVAS). 

The physical property of “elasticity” distinguishes the structural protein elastin from the related structural protein collagen. The close interconnection of collagen and elastin in tissues (e.g., in large blood vessels) confers both elastic and tear-resistant properties.

Histologically, elastin can be visualized using the Elastica van Gieson stain (EvG stain).

Elastin is a very long-lived protein with a half-life of > 70 years. Elastin formation begins even before birth and continues only during the first few years of life.

In the skin, the elastic fibers are responsible for the skin’s tensile state. UV rays have been shown to damage elastin.  It is transformed into a homogeneous, flaky material (elastosis). The (irreversible) UV-induced elastotic degeneration of elastin in the skin is referred to as actinic elastosis. It leads to a loss of elasticity and the formation of wrinkles in the skin.

Elastin is highly resistant to most proteases. The proteases capable of cleaving elastin are called elastases. They can degrade elastin and other scleroproteins—such as collagen types I, II, III, IV, VIII, IX, X, and XI—as well as structural glycoproteins. Physiological antagonists include alpha-1 antitrypsin and alpha-2 macroglobulin. If the level of alpha-1 antitrypsin is insufficient, elastase has a destructive effect (e.g., in pulmonary emphysema). Other diseases in which neutrophil elastase appears to play a significant role include cystic fibrosis, acute respiratory distress syndrome (ARDS), rheumatoid arthritis, and infectious diseases.