Fibronectin structure

Figure 2.28. Structural changes in fibronectin. Structure of fibronectin at high (top) and low (bottom) ionic strength. Note collapse of molecule at low ionic strength.

Collagen IV 550 kDa, two al(IV) and one a2(IV) chains disulfide bonded Extracellular matrix Binds laminin and fibronectin Structural component of basement membranes... 

Isaacs BS, Brew SA, Ingham KC (1989) Reversible unfolding of the gelatin-binding domain of fibronectin structural stability in relation to function. Biochemistry 28 842-855... 

Protein lateral motion is much slower than that of lipids because proteins are larger than lipids. Also, some membrane proteins can diffuse freely through the membrane, whereas others are bound or anchored to other protein structures in the membrane. The diffusion constant for the membrane protein fibronectin is approximately 0.7 X 10 cmVsec, whereas that for rhodopsin is about 3 X 10 cmVsec. 

Fibronectin receptor is a two-chain glycoprotein of the integrin family that serves as a transmembrane linker by binding to talin on the cytoplasmic side and to fibronectin on the external side of the membrane. The pull exerted by stress fibers on attached structures may be produced by bipolar assemblies of nonmuscle myosin molecules producing a sliding of actin filaments of opposite polarity. 

Figure 48-3. Schematic representation of fibronectin. Seven functional domains of fibronectin are represented two different types of domain for heparin, cell-binding, and fibrin are shown. The domains are composed of various combinations of three structural motifs (I, II, and III), not depicted in the figure. Also not shown is the fact that fibronectin is a dimer joined by disulfide bridges near the carboxyl terminals of the monomers. The approximate location of the RGD sequence of fibronectin, which interacts with a variety of fibronectin integrin receptors on cell surfaces, is indicated by the arrow. (Redrawn after Yamada KM Adhesive recognition sequences.

The major components of the ECM are the structural proteins collagen, elastin, and fibrihin a number of specialized proteins (eg, fibronectin and laminin) and various proteoglycans. 

Brummendorf, T. and Rathjen, F. G. Axonal glycoproteins with immunoglobulin and fibronectin type II-related domains in vertebrates Structural features, binding activities and signal transduction. /. Neurochem. 61 1207-1219, 1993. 

The extracellular domain of RPTKs can be composed of different structural motifs. For instance, the EGFR extracellular domain contains two cysteine-rich regions. The PDGFR extracellular domain consists of five immuno-globulin-like repeats. Other domains found in the extracellular region of RPTKs include fibronectin III repeats,... 

Other adhesion receptors that are structurally and functionally related include the receptors for fibronectin, vitronectin, platelet glycoproteins 13b and Ilia and the VLA (very-late antigen) series. All molecules involved in adhesion recognise the RGD motif and require the divalent cations Ca2+ and Mg2+ for binding. All are dimers of glycosylated proteins with relative molecular masses 95-190 kDa. There is also some sequence homology between the /J-chain (CD18) and one chain of the fibronectin receptor. 

Adhesion proteins in this group contain an immunoglobulin domain that is composed of 90-100 amino acids arranged in a sandwich of two sheets of antiparallei strands. Some members of this family also contain fibronectin type III—like domains in addition to the immunoglobulin domain. Immunoglobulin-related adhesion proteins either can exist as transmembrane structures or can be attached to cell membranes via glycosyl phosphatidylinositol links (B4, R5). 

Pearlstein, E. L., 1. Gold, and A. Garcia-Pado (1980). Fibronectin a review of its structure and biological activity. Mol. Cell. Biochem. 29 103-128. 

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