A tetravalent RGD ligand for integrin-mediated cell adhesion.

Monovalent RGD (arginine-glycine-aspartic acid) peptides or polymers furnished with RGD in random distributions are employed as cell-scaffolds and gene delivery vehicles. However, integrin binding to RGD is dependent on the spatial distribution (clustering) of the ligand and intrinsic integrin affinity via conformational changes (avidity). Here we have designed and expressed a polypeptide consisting of a tetrameric coiled coil and spacer facilitating polyvalent (clustered) display of integrin ligands; the RGD motif was used as proof of principle. Size-exclusion chromatography and circular dichroism showed that the polypeptide self assembled as a tetramer in solution with a defined secondary structure. Cell adhesion to surfaces coated with the polypeptide was up to 3-fold greater than that for (monovalent) RGDS peptide at equivalent concentrations. Moreover, the polypeptide in solution at concentrations >or= 1 microM inhibited cell adhesion to fibronectin-coated surfaces, while RGDS peptide in solution at concentrations up to 500 muM did not. These cell data demonstrate that the polypeptide bound integrin receptors in a polyvalent manner. The polypeptide will therefore be of use in the engineering of tissue-culture scaffolds with increased cell adhesion activity, or to targeted gene delivery vehicles, and could incorporate protein ligands in place of the RGD motif.