Structural Macromolecules: Laminins, Entactin/Nidogen, and Proteoglycans (Perlecan, Agrin)

This chapter focuses on structural macromolecules—laminins, entactin/nidogen, and proteoglycans. The discovery of a large‐molecular weight glycoprotein, known as “laminin,” along with the presence of collagen type IV, established the heterogeneity of the macromolecular components of basement membranes. The term “laminin” refers to a family of at least 15 proteins. The chapter defines the general structure of the protein and examines the structure of the protein chains. It also indicates the nature and place of the glycan chains bound to the protein. The structures of various trimers, the association of the chains among themselves, and their spatial arrangement are also described in the chapter. It also reviews the nature of the genes encoding every chain. The commonest isoform of laminin—laminin-1—is the most extensively studied and is the most abundant in embryo basement membranes. Entactin/nidogen is a sulfated 150‐kDa glycoprotein. They have been numbered 1 and 2, are composed of a single polypeptide, and are encoded by separate genes. Entactin/nidogen‐1 is the quantitatively predominant form.