Laminin

Laminins are a family of glycoproteins of the extracellular matrix of all animals. They are major constituents of the basement membrane, namely the basal lamina (the protein network foundation for most cells and organs). Laminins are vital to biological activity, influencing cell differentiation, migration, and adhesion. Laminins are heterotrimeric protein complexes with a high molecular mass (~400 to ~900 kDa) and possess 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, e.g. laminin-511 contains α5, β1, and γ1 chains. Fourteen other chain combinations have been identified in vivo. The trimeric proteins intersect, composing a cruciform structure that is able to bind to other molecules of the extracellular matrix and cell membrane. The three short arms have an affinity for binding to other laminin molecules, conducing sheet formation. The long arm is capable of binding to cells and helps anchor organized tissue cells to the basement membrane. Laminins are integral to the structural scaffolding of almost every tissue of an organism—secreted and incorporated into cell-associated extracellular matrices. These glycoproteins are imperative to the maintenance and vitality of tissue; defective laminins can cause muscles to form improperly, leading to a form of muscular dystrophy, lethal skin blistering disease (junctional epidermolysis bullosa), and/or defects of the kidney filter (nephrotic syndrome).