The elastic properties of many tissues such as the lung, dermis, and large blood 
vessels are due to the presence of elastic fibers in the extracellular space. 
These fibers have been shown by biochemical and ultrastructural analysis to be 
composed of two distinct components, a more abundant amorphous component and a 
10-12 nm microfibrillar component, which is located primarily around the 
periphery of the amorphous component. The protein elastin makes up the highly 
insoluble amorphous component and is responsible for the elastic properties. 
Elastin is found throughout the vertebrate kingdom and possesses an unusual 
chemical composition rich in glycine, proline, and hydrophobic amino acids, 
consonant with its characteristic physical properties. The 72-kDa biosynthetic 
precursor, tropoelastin, is secreted into the extracellular space where it 
becomes highly cross-linked into a rubber-like network through the activity of 
the copper-requiring enzyme lysyl oxidase. Analysis of the elastin gene has 
demonstrated that hydrophobic and cross-linking domains are encoded in separate 
exons and that there is significant alternative splicing, resulting in multiple 
isoforms of tropoelastin. The elastin gene promoter contains many potential 
binding sites for various modulating factors indicative of a complex pattern of 
transcriptional regulation. The microfibrils contain several proteins, including 
fibrillin, and probably act as an organizing scaffold in the formation of the 
elastin network. There appears to be a fibrillin gene family in which each 
protein contains multiple repeats of a motif previously found in epidermal 
growth factor and a second motif observed in transforming growth factor beta 
1-binding protein. Mutations in the fibrillin gene located on human chromosome 
15 have been strongly implicated as the cause of the Marfan syndrome.