Entactin

Basal laminas are specialized areas of the ECM that surround epithelial and some other cells (eg, muscle cells) here we discuss only the laminas found in the renal glomerulus. In that strucmre, the basal lamina is contributed by two separate sheets of cells (one endothelial and one epithelial), each disposed on opposite sides of the lamina these three layers make up the glomerular membrane. The primary components of the basal lamina are three proteins—laminin, entactin, and type IV collagen—and the GAG heparin or heparan sulfate. These components are synthesized by the underlying cells. 

Laminin [consisting of three polypeptide chains, A, Bl (possibly replaced in GBM by S) and B2] is the most important noncollagenous protein of the glomerular basement membrane. Laminin forms a second network, which is connected to the collagen IV network probably via another protein called entactin or nidogen. Laminin is probably very important for cellular differentiation and adhesion, but its mesh clearly also contributes to the structure of the glomerular basement membrane. The postnatally common embryonic laminin-10 isoform is... 

Cell attachment to the glomerular basement membrane is mediated by laminin, entactin, and fibronectin, at least partly through integrin receptors on the cell surface of both endothelial and visceral epithelial cells. 

Interstitial collagenase MMP-1 Collagen types I, II, III, VII, and X, gelatin, entactin, aggrecan... 

Gelatinase B MMP-9 Collagen types IV, V, XIV, aggrecan, elastin, entactin, vitronectin... 

Nidogen/entactin Single chain (A/, 150K) Laminin binding... 

The main constituents of the extracellular matrix are (1.) collagen, particularly the fibrillary types I (36%), III (36%) and V (16%) as well as the non-fibrillary types FV (9%), VI (0.2%) and to a minor degree also type VII, (2.) glycoproteins (fibronectin, tenascin, laminin, undulin, elastin, entactin), and (2.) proteoglycans of both the core protein and the glycosaminoglycan type (e.g. chondroitin, heparan sulphate, hyaluronic add, dermatan sulphate). 

A ubiquitous laminin-associated glycoprotein is entactin (also known as nidogen), a glycoprotein now thought to provide linkage between laminin and type IV collagen in basement membranes. 

FIGURE 6-13 Major components of the basal lamina. Schematic model of basal lamina showing the organization of the major protein components. Type IV collagen and laminin each form two-dimensional networks, which are cross-linked by entactin and perlecan molecules. [Adapted from B. Alberts et al., 1994, Molecular Biology of the Cell, 3d ed., Garland, p. 991.1... 

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