The laminins.

Laminins are extracellular matrix proteins which consist of alpha, beta and gamma chains with molecular masses of 140-400 kDa. Chain association occurs through a large triple alpha-helical coiled-coil domain towards the C-terminus of each chain. Eight genetically distinct laminin chains (alpha 1, alpha 2, alpha 3, beta 1, beta 2, beta 3, gamma 1, gamma 2) and seven different assembly forms (laminins-1 to -7) are known so far. The most extensively characterized laminin-1 (alpha 1 beta 1 gamma 1) shows calcium-dependent self assembly and heterotypic binding to perlecan, nidogen, fibulin-1 and other matrix components. This binding indicates a crucial role in the supramolecular organization of basement membranes. Laminins also possess binding sites for at least six different integrin receptors and are thus involved in many cell-matrix interactions. Such interactions have been shown to be important during embryonic development and for tissue homeostasis and remodelling.