Elastin

Elastin is a highly elastic is_associated_with::protein in is_associated_with::connective tissue and allows 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. In humans, elastin is encoded by the ELN is_associated_with::gene.

Function
The ELN gene encodes a protein that is one of the two components of elastic fibers. The encoded protein is rich in is_associated_with::hydrophobic amino acids such as is_associated_with::glycine and is_associated_with::proline, which form mobile hydrophobic regions bounded by crosslinks between is_associated_with::lysine residues. Multiple transcript variants encoding different isoforms have been found for this gene. The other name for elastin 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 is_associated_with::cutis laxa. Other associated defects in elastin include is_associated_with::Marfan syndrome, is_associated_with::emphysema caused by α1-antitrypsin deficiency, is_associated_with::atherosclerosis, is_associated_with::Buschke-Ollendorff syndrome, is_associated_with::Menkes syndrome, is_associated_with::pseudoxanthoma elasticum, and is_associated_with::Williams syndrome.

Composition
is_associated_with::Elastic fiber is composed mainly of an amorphous component, which is extensively cross-linked elastin, and a fibrillar component, which are primarily the microfibrils such as is_associated_with::fibrillin, both of which are made of simple is_associated_with::amino acids such as is_associated_with::glycine, is_associated_with::valine, is_associated_with::alanine, and is_associated_with::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. Elastin is made by linking many soluble is_associated_with::tropoelastin protein molecules, in a reaction catalyzed by is_associated_with::lysyl oxidase, to make a massive insoluble, durable complex cross-linked by is_associated_with::desmosine and is_associated_with::isodesmosine in an in vivo is_associated_with::Chichibabin pyridine synthesis reaction. The amino acid responsible for these cross-links is is_associated_with::lysine. Tropoelastin is a specialized protein with a molecular weight of 64 to 66 kDa, and an irregular or random coil conformation made up of 830 amino acids.

Molecular biology
In mammals, only a single gene for ELN is present. In humans, the ELN gene is a 45 kb segment that lies on is_associated_with::chromosome 7, and has 34 exons interrupted by almost 700 introns, with the first exon being a is_associated_with::signal peptide assigning its extracellular localization. The large number of introns suggests that is_associated_with::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. Due to is_associated_with::alternative splicing, there are at least 11 known human tropoelastin isoforms, and are under developmental regulation. However, there are minimal differences among tissues at the same developmental stage.

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