Elastin

ELN
Identifiers
Aliases	ELN, SVAS, WBS, WS, elastin, ADCL1
External IDs	OMIM: 130160 GeneCards: ELN
Gene location (Human) Chr. Chromosome 7 (human) Band 7q11.23 Start 74,027,789 bp End 74,069,907 bp
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in ascending aorta right coronary artery right lung popliteal artery gastric mucosa left coronary artery upper lobe of left lung gallbladder canal of the cervix left uterine tube n/a More reference expression data BioGPS n/a
Gene ontology Molecular function extracellular matrix structural constituent protein binding extracellular matrix constituent conferring elasticity extracellular matrix binding Cellular component extracellular region elastic fiber extracellular matrix collagen-containing extracellular matrix Biological process animal organ morphogenesis cell population proliferation extracellular matrix disassembly extracellular matrix organization blood circulation respiratory gaseous exchange by respiratory system outflow tract morphogenesis aortic valve morphogenesis skeletal muscle tissue development regulation of actin filament polymerization stress fiber assembly regulation of smooth muscle cell proliferation Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 2006 n/a Ensembl ENSG00000049540 n/a UniProt P15502 n/a RefSeq (mRNA) NM_000501 NM_001081752 NM_001081753 NM_001081754 NM_001081755 NM_001278912 NM_001278913 NM_001278914 NM_001278915 NM_001278916 NM_001278917 NM_001278918 NM_001278939 n/a RefSeq (protein) NP_000492 NP_001075221 NP_001075222 NP_001075223 NP_001075224 NP_001265841 NP_001265842 NP_001265843 NP_001265844 NP_001265845 NP_001265846 NP_001265847 NP_001265868 n/a Location (UCSC) Chr 7: 74.03 – 74.07 Mb n/a PubMed search n/a
Wikidata
View/Edit Human

Thick elastic fibers consisting of bundles of elsatin in the human lung

Elastin is a protein that in humans is encoded by the ELN gene. Elastin is a key component of the extracellular matrix in gnathostomes (jawed vertebrates). It is highly elastic and present in connective tissue allowing many tissues in the body to resume their shape after stretching or contracting. Elastin helps skin to return to its original position when it is poked or pinched. Elastin is also an important load-bearing tissue in the bodies of vertebrates and used in places where mechanical energy is required to be stored.

Function

The ELN gene encodes a protein that is one of the two components of elastic fibers. The encoded protein is rich in hydrophobic amino acids such as glycine and proline, which form mobile hydrophobic regions bounded by crosslinks between lysine residues. Multiple transcript variants encoding different isoforms have been found for this gene. Elastin's soluble precursor is tropoelastin. The characterization of disorder is consistent with an entropy-driven mechanism of elastic recoil. It is concluded that conformational disorder is a constitutive feature of elastin structure and function.

Clinical significance

Deletions and mutations in this gene are associated with supravalvular aortic stenosis (SVAS) and the autosomal dominant cutis laxa. Other associated defects in elastin include Marfan syndrome, emphysema caused by α₁-antitrypsin deficiency, atherosclerosis, Buschke-Ollendorff syndrome, Menkes syndrome, pseudoxanthoma elasticum, and Williams syndrome.

Elastosis

Elastosis is the buildup of elastin in tissues, and is a form of degenerative disease. There are a multitude of causes, but the most commons cause is actinic elastosis of the skin, also known as solar elastosis, which is caused by prolonged and excessive sun exposure, a process known as photoaging. Uncommon causes of skin elastosis include elastosis perforans serpiginosa, perforating calcific elastosis and linear focal elastosis.

Skin elastosis causes

Condition	Distinctive features	Histopathology
Actinic elastosis (most common, also called solar elastosis)	Elastin replacing collagen fibers of the papillary dermis and reticular dermis
Elastosis perforans serpiginosa	Degenerated elastic fibers and transepidermal perforating canals (arrow in image points at one of them)
Perforating calcific elastosis	Clumping of short elastic fibers in the dermis.
Linear focal elastosis	Accumulation of fragmented elastotic material within the papillary dermis and transcutaneous elimination of elastotic fibers.

Composition

Stretched elastin isolated from bovine aorta

In the body, elastin is usually associated with other proteins in connective tissues. Elastic fiber in the body is a mixture of amorphous elastin and fibrous fibrillin. Both components are primarily made of smaller amino acids such as glycine, valine, alanine, and proline. The total elastin ranges from 58 to 75% of the weight of the dry defatted artery in normal canine arteries. Comparison between fresh and digested tissues shows that, at 35% strain, a minimum of 48% of the arterial load is carried by elastin, and a minimum of 43% of the change in stiffness of arterial tissue is due to the change in elastin stiffness.

Tissue distribution

Elastin serves an important function in arteries as a medium for pressure wave propagation to help blood flow and is particularly abundant in large elastic blood vessels such as the aorta. Elastin is also very important in the lungs, elastic ligaments, elastic cartilage, the skin, and the bladder. It is present in jawed vertebrates.

Characteristics

Elastin is a very long-lived protein, with a half-life of over 78 years in humans.

Clinical research

The feasibility of using recombinant human tropoelastin to enable elastin fiber production to improve skin flexibility in wounds and scarring has been studied. After subcutaneous injections of recombinant human tropoelastin into fresh wounds it was found there was no improvement in scarring or the flexibility of the eventual scarring.

Biosynthesis

Tropoelastin precursors

Elastin is made by linking together many small soluble precursor tropoelastin protein molecules (50-70 kDa), to make the final massive insoluble, durable complex. The unlinked tropoelastin molecules are not normally available in the cell, since they become crosslinked into elastin fibres immediately after their synthesis by the cell, after their export into the extracellular matrix.

Each tropoelastin consists of a string of 36 small domains, each weighing about 2 kDa in a random coil conformation. The protein consists of alternating hydrophobic and hydrophilic domains, which are encoded by separate exons, so that the domain structure of tropoelastin reflects the exon organization of the gene. The hydrophilic domains contain Lys-Ala (KA) and Lys-Pro (KP) motifs that are involved in crosslinking during the formation of mature elastin. In the KA domains, lysine residues occur as pairs or triplets separated by two or three alanine residues (e.g. AAAKAAKAA) whereas in KP domains the lysine residues are separated mainly by proline residues (e.g. KPLKP).

Aggregation

Tropoelastin aggregates at physiological temperature due to interactions between hydrophobic domains in a process called coacervation. This process is reversible and thermodynamically controlled and does not require protein cleavage. The coacervate is made insoluble by irreversible crosslinking.

Crosslinking

To make mature elastin fibres, the tropoelastin molecules are cross-linked via their lysine residues with desmosine and isodesmosine cross-linking molecules. The enzyme that performs the crosslinking is lysyl oxidase, using an in vivo Chichibabin pyridine synthesis reaction.

Molecular biology

Domain structure of human tropoelastin

In mammals, the genome only contains one gene for tropoelastin, called ELN. The human ELN gene is a 45 kb segment on chromosome 7, and has 34 exons interrupted by almost 700 introns, with the first exon being a signal peptide assigning its extracellular localization. The large number of introns suggests that genetic recombination may contribute to the instability of the gene, leading to diseases such as SVAS. The expression of tropoelastin mRNA is highly regulated under at least eight different transcription start sites.

Tissue specific variants of elastin are produced by alternative splicing of the tropoelastin gene. There are at least 11 known human tropoelastin isoforms. these isoforms are under developmental regulation, however there are minimal differences among tissues at the same developmental stage.

See also

• Cutis laxa
• Elastic fibers
• Elastin receptor
• Resilin: an invertebrate protein
• Williams syndrome

Further reading

External links

• Elastin at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
• Histology image: 21402loa – Histology Learning System at Boston University
• GeneReviews/NIH/NCBI/UW entry on Williams or Williams-Beuren Syndrome
• The Elastin Protein
• Microfibril

This article incorporates text from the United States National Library of Medicine, which is in the public domain.