Elastin is a rubberlike protein with fibres that can stretch to many times their normal length. It is a highly hydrophobic protein which must be secreted by cells as the soluble biosynthetic precursor tropoelastin in in order to prevent the formation of hydrophobic aggregates that would be potentially fatal for the cell. Upon secretion the tropoelastin molecules can be assembled into extensive elastic fibres and sheets by cross-linking. Cross-linking occurs between the amino acids lysine and alanine through condensation reactions between their respective side chains.

Elastin is predominantly composed of small, non-polar amino acids, with the smallest of the amino acids, Glycine making up one third of its residues and over a third made up of alanine and valine residues. It is also rich in proline.

Elastin's primary structure consists of alternating hydrophobic segments (supposedly responsible for the protein's elasticity) and alanine and lysine-rich alpha helical segments responsible for cross-linking with adjacent elastin molecules. Each segment is encoded by separate exons. It is thought that elastin has a random coil formation in its "relaxed" state which can be stretched out while cross-links between chains hold the molecules together and collagen fibrils are interwoven with the fibres to limit stretching and prevent tearing. The exact conformation of the fibres and the way in which elastin's structure provides it with its rubber-like properties are still subject to debate. In addition elastin fibres are covered with a sheath of microfibrils composed of glycoproteins such as fibrillin which are required for assembly and to maintain the integrity of the fibre. A genetic disease known as Marfan's Syndrome involves a mutation of the fibrillin gene and in severe cases can render the the aorta prone to rupture.

Elastin networks in the extracellular matrix are essential for the functioning of such organs as lungs, skin and blood vessels which require strong but elastic tissue.

The information presented here was taken from Molecular Biology of the Cell (4th edition), by Alberts et al., Garland Sciences, USA, (2002) and Biochemistry (2nd edition), by Voet D and Voet J G, John Wiley & Sons, Inc., 1995.