Laminin is a large, complex glycoprotein that is a major component of the extracellular matrix. It is composed of three polypeptide chains, α, β, and γ, which are arranged in a cruciform shape. The α chain is the largest and most heavily glycosylated, and it contains a number of globular domains that are involved in binding to other proteins. The β and γ chains are smaller and less heavily glycosylated, and they contain a number of cysteine-rich domains that are involved in disulfide bond formation.

Laminin is secreted by a variety of cells, including epithelial cells, endothelial cells, and Schwann cells. It plays a number of important roles in the extracellular matrix, including:

* Providing structural support

* Facilitating cell adhesion and migration

* Regulating cell differentiation and proliferation

* Promoting angiogenesis (the formation of new blood vessels)

Laminin is also involved in a number of pathological processes, including cancer, fibrosis, and arthritis.