RGD domain

Chimeric recombinant systems have also been developed, in an effort to combine the mechanical properties of silks with the biological features of other macromolecules. In one study, the consensus sequence of the major component of the dragline silk from Nephila clavipes was bioengineered into protein variants that incorporated RGD domains and expressed in E. coli. These recombinant proteins were able to maintain their beta-sheet forming abilities and were processable into films and fibers. Both RGD recombinant and recombinant silk without RGD supported human mesenchymal stem cell (hMSC) attachment and osteogenic differentiation. A separate study reported the fusion of domains from the major amplullate... 

YAVTGRDGSPASSKPIA((VPGIG)2VPGKG(VPGIG)2)4VP)3-LE Scrambled RGD Elastin-Iike domain... 

Fig. 15 Amino acid sequences of artificial extracellular matrix (aECM) proteins. Each protein contains a TV tag, a histidine tag, a cleavage site, and elastin-like domains with lysine residues for crosslinking. The RGD cell-binding domain is found in aECM 1, whereas aECM 3 contains the CS5 cell-binding domain. aECM 2 and aECM 4 are the negative controls with scrambled binding domains for aECM 1 and aECM 3, respectively. Reprinted from [121] with permission from American Chemical Society, copyright 2004...

In another study, the original repetitive Cio, (AGAGAGPEG)io, center was reconstructed into nine repeats of AGAGAGPEG with three distributed repeats of the RGD sequence. The new triblock protein, composed of acidic and basic terminal domains in addition to the reconstructed central block, has been shown to support adhesion, spreading, and polarization of human fibroblast cells [82]. Triblock polypeptides that facilitate antibody binding have also been reported [83]. 

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 conformation and orientation of adsorbed proteins has been examined with monoclonal antibodies that recognize a specific site in a protein of interest. Keselowsky et al. examined the conformation of Fn adsorbed to SAMs that carried methyl, hydroxyl, carboxyl, and amine groups [79]. They used monoclonal antibodies that recognized the central cell-binding domain of Fn near the RGD motif. Different SAM functionalities differentially modulated the binding affinities of the monoclonal antibodies (OH > COOH = NH2 > CH3). The strength of cell adhesion to these... 

Pierschbacher and Ruoslahti [130] in 1984 reported that the ability of fibronec-tin to bind cells can be accounted for by the tetrapeptide L-arginyl-glycyl-L-aspartyl-L-serine (RGDS), a sequence which is part of the cell attachment domain of fibronectin. They examined the cell-attachment activity of several... 

As a sidebar, it should be noted that there is a domain on the fibronectin molecule which binds to the simple peptide RGD (arginine-glycine-aspartic acid) and this has been explored as a means of interfering with the tumor adhesion process using longer, more stable, polypeptide sequences and other analogues or derivatives (Humphries et al. 1987). 

FIGURE 9.6 Structure features of integrin receptors. Peptides or proteins containing the tripeptide sequence of RGD are recognized by several integrins present in the tumor cells. However, the protein tails pass through the plasma membrane with the hydrophobic domains and are locked into place. (From dos Santos, 2005)... 

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