Laminins are a family of glycoproteins of the extracellular matrix of all animals. They are major components of the basal lamina (one of the layers of the basement membrane), the protein network foundation for most cells and organs. The laminins are an important and biologically active part of the basal lamina, influencing cell differentiation, migration, and adhesion.
Laminins are heterotrimeric proteins with a high molecular mass (~400 to ~900 kDa). They contain three different chains (α, β and γ) encoded by five, four, and three paralogous genes in humans, respectively. The laminin molecules are named according to their chain composition. Thus, laminin-511 contains α5, β1, and γ1 chains. Fourteen other chain combinations have been identified in vivo. The trimeric proteins intersect to form a cross-like structure that can bind to other cell membrane and extracellular matrix molecules. The three shorter arms are particularly good at binding to other laminin molecules, which allows them to form sheets. The long arm is capable of binding to cells, which helps anchor organized tissue cells to the basement membrane.
The laminin family of glycoproteins is an integral part of the structural scaffolding in almost every tissue of an organism. They are secreted and incorporated into cell-associated extracellular matrices. Laminin is vital for the maintenance and survival of tissues. Defective laminins can cause muscles to form improperly, leading to a form of muscular dystrophy, lethal skin blistering disease (junctional epidermolysis bullosa) and defects of the kidney filter (nephrotic syndrome).
In humans, fifteen laminin trimers have been identified. The laminins are combinations of different alpha-, beta-, and gamma-chains.
Five alpha-chain isoforms: LAMA1, LAMA2, LAMA3 (which has three splice forms), LAMA4, LAMA5
Four beta-chain isoforms: LAMB1, LAMB2, LAMB3, LAMB4 (note that no known laminin trimer incorporates LAMB4 and its function remains poorly understood)
Three gamma-chain isoforms: LAMC1, LAMC2, LAMC3
Laminins were previously numbered as they were discovered, i.