Identification of a region in the integrin beta 3 subunit that confers ligand binding specificity

Many integrin adhesion receptors bind ligands containing the Arg-Gly-Asp (RGD) peptide motif, Most integrins exhibit considerable specificity for particular ligands and can distinguish among the many conformations of RGD. In this study we identify the domain of the integrin beta subunit involved in determining ligand binding specificity, Chimeras of beta 3 and beta 5, the most homologous integrin beta subunits, were expressed with alpha v on the surface of human 293 cells, The ligand binding phenotype of each chimera was assessed using the ligands Fab-9 and fibrinogen, both of which have a binding preference for alpha v beta 3. The results of the study show that when exons C and D of the beta 3 subunit (residues 95-233) are substituted into beta 5, the chimera gained the ability to bind Fab-9 with an affinity close to that of wild-type alpha v beta 3. This chimera was able to mediate cell adhesion to fibrinogen. Furthermore, the swap of only a 39-residue segment of this larger domain, beta 3 residues 164-202, into the backbone of beta 5 enabled the chimeric integrin to bind soluble Fab-9. This small domain is highly divergent among the integrin beta subunits, suggesting that it may play a role in determining ligand selection by all integrins.