Laminin glycoproteins

Helix bundles. A third peptide chain can be added to a coiled coil to form a triple-stranded bundle.180-183 An example is the glycoprotein laminin found in basement membranes. It consists of three peptide chains which, for -600 residues at their C-terminal ends, form a three-stranded coil with heptad repeats.182184 Numerous proteins are folded into four helical segments that associate as four-helix bundles (Fig. 2-22).185-188 These include electron carriers, hormones, and structural proteins. The four-helix bundle not only is a simple packing arrangement, but also allows interactions between the + and - ends of the macro-dipoles of the helices. 

In the extracellular matix, fibronectin serves as the matrix organizer. This is still poorly understood, but it is known that fibronectin can interact with proteoglycans, collagens, and cells enmeshed in the matrix, where it binds cells together and anchors them to the matrix. This function also follows fibronectin to act as a mediator of cell growth and differentiation. In some cell systems such as the epithelial cells, this function is replaced by another tissue glycoprotein, laminin. 

McCarthy, J. B., Palm, S. L. and Furcht, L. T (1983). Migration by haptotaxis of a Schwann cell tumor line to the basement membrane glycoprotein laminin. J. Cell Biol. 97,772-777. 

In some cell types, fibronectin is not involved in cell adhesion. For example, the extracellular matrix adjacent to epithelial cells and chondrocytes does not contain fibronectin but rather two other glycoproteins, laminin and chondronectin. Laminin mediates in adhesion of epithelial cells, whereas chondronectin mediates... 

Thus, while glycoprotein Ia/IIa (a2Pj) binds to collagen, glycoprotein Ic/IIa (a ) binds to fibronectin (5). The other integrin belonging to the beta 1 family that is involved in platelet adhesion is ct6P, which binds laminin. 

Cell interactions leading to kidney-tubule determination are tunica-mycin-sensitive. When tunicamycin was applied at concentrations that prevent induction of differentiation, cells did not contain laminin, a glycoprotein that is detected in early stages of differentiation. As tunicamycin did not prevent differentiation when applied later during the morphogenetic period, the authors considered it unlikely that the drug interferes with tubule formation by inhibiting the secretion of laminin.493,494... 

While one end of the dystrophin molecule binds to actin filaments, the C-terminal domain associates with several additional proteins to form a dystrophin-glycoprotein complex (see figure)/1 k Dystrophin is linked directly to the membrane-spanning protein P-dystroglycan, which in the outer membrane surfaces associates with a glycoprotein a-dystroglycan. The latter binds to laminin-2 (Fig. 8-33), a protein that binds the cell to the basal lamina. Four... 

Ervasti, J. M., and Campbell, K. P. (1993b). A role for the dystrophin-glycoprotein complex as a transmembrane linker between laminin and actin. J. Cell Biol. 122, 809-823. 

Figure 1. The muscle dystrophin-glycoprotein complex. The dystrophin-glycoprotein complex normally spans the plasma membrane of the skeletal muscle cell and may stabilize the sarcolemma and cytoskeleton to allow force transduction between the intracellular cytoskeleton (F-actin filaments) and the extracellular matrix. The molecules indicated are core components of the dystrophin-glycoprotein complex. Laminin 2 is the predominant laminin isoform in skeletal muscle basement membranes. Modified from McNeil and Steinhardt (2003)...

Glycoproteins Fibronectin, laminin, merosin, tenascin, nidogen, undulin, hyaluronic acid... 

Laminin Glycoprotein Amino acids and disaccharides Attachment factor, component of basement membrane... 

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