Structure and Organization of Macromolecules in Basement Membranes
This chapter summarizes some of the evidence on the macromolecular organization of basement membranes. It describes structural aspects of type IV collagen and then of the noncollagenous components laminin, entactin, and proteoglycans. The chapter considers the various supramolecular models proposed in the literature and offer arguments for their validity or invalidity. It details the isolation and characterization of mouse and human cDNA clones for the α1 and α2 chains of type IV collagen as well as for the B-1 chain of mouse tumor laminin. The collagen component of basement membrane has been isolated and characterized chemically, immunologically, and ultrastructurally. Laminin is a major noncollagenous glycoprotein component of basement membranes. The supramolecular organizations probably are determined by the relative proportions and types of the individual components and perhaps, to the temporal sequence of their deposition into the extracellular matrix.