Elastin fibers are connective tissues that can stretch when hydrated and return to their original length after being stretched. They comprise a significant portion of the dry weight of ligaments, lungs, larger blood vessels such as aorta, and skin.
Elastin is a polymer of tropoelastin monomers, which contain 850 amino acids, predominantly valine, praline, glycine, and alanine. When tropoelastin molecules associate to form a fiber, lysine residues cross-link by forming desmosine and isodesmosine, which are unique to elastin. Mutations in the elastin gene can cause cutis laxa and supravalvular aortic stenosis.
Elastases, which are serine proteases, are capable of degrading elastin. Elastases are located in tissues, macrophages, leukocytes, and platelets. Such elastases may contribute to blood vessel wall damage and aneurysm formation in the vasculitides.
Urinary desmosine levels are used as a measure of elastin degradation.
Fbrillins are large glycoproteins that function as part of the microfibrillar proteins, which are associated with an elastin core. Fibrillin can also be found as isolated bundles of microfibrils in skin, blood vessels, and several other tissues. Abnormalities in fibrillin-1 are thought to cause Marfan’s syndrome, while abnormalities in fibrillin-2 cause contractural arachnodactyly.
Adhesins are cell-binding glycoproteins that can be present in intracellular matrices and basement membranes. They are distributed and named as follows
- Fibronectin-connective tissue
- Laminin-basement membrane
- Chondroadherin-cartilage
- Osteoadherin-bone
These glycoproteins have specific adhesive and other important properties. They bind cells by attaching to integrins on cells. Some have the classical arginin-glycine-aspartic acid cell-binding sequence.
