Laminin Polymerization and Binding to Glycosaminoglycans: A Hypothesis for Modulation of Basement Membrane Structure
Typical basement membranes (BMs) are sheet-like extracellular matrices composed of a lamina lucida and lamina densa. They support and anchor cells, regulate growth and differentiation, divide tissue compartments and selectively filter the passage of macromolecules from one side to the other. Common to most BMs are a set of protomers, or “building blocks”, which assemble into a biological matrix: these include type IV collagen, laminin, nidogen and heparan sulfate proteoglycans and smaller amounts of other components. These components self-assemble with specific binding interactions into one or more molecular architectures [Yurchenco et al.,1986; Yurchenco & Ruben,1988]. Functions of BMs such as support and sieving are expected to be dependent on both the presence of protein domain determinants as well as their supramolecular arrangement in three-dimensional space. Similarly cell-matrix interactions are probably dependent on architecture as well. A matrix protein with a cell binding domain, for example, cannot interact with the cell if its domain is inaccessible by virtue of its geometrical position in the matrix: evidence has been presented that this is the case with the central cell-binding domain of laminin in the corneal epithelial BM [Schittny et al., 1988].
KeywordsPermeability Magnesium Heparin Polysaccharide Sedimentation
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