27.10: Laminins are the Adhesive Proteins of Basal Lamina

Laminins are heterotrimeric proteins with high molecular mass found in the extracellular matrix. Each laminin molecule is composed of three chains, viz. alpha, beta, and gamma, coded by five, four, and three paralogous genes, respectively. Laminins are categories based on the compositions of the three chains.

In humans, the five forms of alpha chains are LAMA 1, LAMA 2, LAMA 3, LAMA 4, and LAMA 5. The four forms of beta chains are LAMB 1, LAMB 2, LAMB 3, and LAMB 4. The three forms of gamma chains are LAMC 1, LAMC 2 and LAMC 3.

In the extracellular matrix, the laminins associate with each other to form a mesh. This mesh is associated with other macromolecules like perlecan, entactin, and type IV collagen to form a framework for the basal lamina. Laminins also connect with the cell by binding to their integrins or dystroglycan.

Biologically laminins help in influencing cell adhesion, differentiation, and migration. Laminins are essential for the survival and maintenance of the tissue. Defective laminins can lead to improper muscle formation, skin blistering, and issues related to kidney filtration. Laminins also play an essential role in neural development and peripheral nerve repair.

Laminins are multi-adhesive glycoproteins found in basal lamina. They are composed of three polypeptide chains, alpha, beta and gamma, covalently linked by multiple disulfide bonds.

These chains are twisted together at the C-terminus end, while they remain separated at the N-terminus.

The laminin G - like  domain at the C-terminus of the alpha subunit interacts with proteins such as integrin and dystroglycan present in the cell membrane. This contributes primarily toward cell attachment and helping to exchange signals between intracellular and extracellular matter.

The N-terminal end interacts with other laminins to form a mesh-like network. It further associates with type IV collagen, perlecan, and entactin to form the basal lamina.