Elastin

Elastin is a fibrillar protein with a molecular weight of about 68 kDa ^[1] . Elastin contains about 27% glycine , 19% alanine , 10% valine , 4.7% leucine . The presence of a large number of hydrophobic radicals prevents the creation of a stable globule ; as a result, elastin polypeptide chains do not form regular secondary and tertiary structures ^[2] .

In mammals, elastin is encoded by the ELM gene ^{[1] [3]} and is synthesized by fibroblasts . The synthesis of elastin begins in fibroblasts with the formation of the elastin precursor - the tropoelastin protein. Tropoelastin is a soluble monomer, the hydrophilic sites of which are enriched in lysine residues . In the intercellular matrix with the participation of a copper-dependent lysyl oxidase, lysine residues are oxidized to allisin, which form cross-links that stabilize the elastin molecule. As a result of other post-translational modifications of lysine residues in the composition of elastin molecules, atypical amino acids desmosin and isodesmosin also appear that can be part of several peptide chains simultaneously. Due to this, elastin filaments are combined into a network by strong covalent bonds ^[2] .

Elastin is characterized by insolubility, high stability and low metabolic rate. Most proteinases are unable to break down elastin. Elastin cleavage during reconstructions of connective tissue involves elastase of polymorphonuclear leukocytes, endopeptidase, which predominantly cleaves the bonds formed by the carboxyl groups of aliphatic amino acids. It is active in a slightly alkaline environment (pH 7.5-8.5) and hydrolyzes not only elastin in the extracellular space, but also other proteins - proteoglycans, hemoglobin, collagen, immunoglobulins. Elastase activity inhibits the protein α1-antitrypsin (α1-AT). The largest amount of α1-AT is synthesized by the liver and is in the blood. In tissues, α1-AT is synthesized by macrophages. ^[2]

When digesting meat, elastin is hydrolyzed by pancreatic enzyme pancreatic elastase.

Elastin, along with collagen and some other fibrillar proteins, is located in the intercellular substance ( matrix ) of connective tissue, forming a three-dimensional network of protein fibers. This network is not only important for the mechanical strength of the tissue, but also provides contacts between cells, forms the migration paths of cells along which they can move (for example, during embryonic development), isolates different cells and tissues from each other (for example, provides glide in joints ) ^[4] .

Elastin performs important functions in organs subject to constant stretching and compression, for example, in arteries , lungs , skin , tendons , various sphincters ^[5] . Elastin and collagen fibers help organs to restore their original size after stretching, for example, when pinched the skin or after emptying the bladder ^[6] . With a decrease in the formation of desmosins (or their absence), cross-linking between the elastin fibers is formed in insufficient quantity or does not form at all. As a result, the tensile strength of elastic fabrics decreases and disturbances such as thinning, lethargy, and extensibility appear, i.e. their rubbery properties are lost. Clinically, such disorders can be manifested by cardiovascular changes ( aneurysms and aortic ruptures, defects in the heart valves ), frequent pneumonia and pulmonary emphysema ^[7] . In case of violation of elastin synthesis in the body as a result of a mutation of the ELM gene, a hereditary artery disease, supravalvular aortic stenosis (SVAS) develops ^[3] .