EPITOPES OF ADHESION-PERTURBING MONOCLONAL-ANTIBODIES MAP WITHIN A PREDICTED ALPHA-HELICAL DOMAIN OF THE INTEGRIN BETA-1 SUBUNIT

Several recent studies have demonstrated the involvement of various do mains of the pr integrin subunit in ligand binding, Thus, specific ami no acids have been shown to be important in divalent cation binding, a nd others have been implicated by peptide crosslinking to play an inti mate role in integrin-ligand interactions, Added to these data are pre vious observations that a group of adhesion-blocking anti-chicken beta (1) antibodies mapped within the first 160 amino acid residues of the subunit. These observations suggested that this region plays a critica l role in integrin ligand recognition. In order to further define the domain in which the epitopes for these antibodies are clustered, a ser ies of mouse/chicken chimeric beta(1) constructs were examined for the ir reactivity with each of these antibodies. Most of the antibodies re cognize a region between residues 124 to 160 of the chicken beta(1) su bunit, Computer modeling predicted a possible amphipathic alpha-helica l configuration for the region between residues 141 to 160, Consistent with this prediction, circular dichroism and NMR analysis revealed a tendency for a synthetic peptide containing these residues to form an alpha-helix, The significance of this structural characteristic was de monstrated by a mutation at residue 149 that disrupted the alpha-helix formation and resulted in a loss of the ability to form heterodimers with a subunits, localize to focal contacts, or be transported to the cell surface, The direct involvement of residues 141 to 160 in ligand binding was supported by the ability of a peptide with this sequence t o elute integrins from a fibronectin affinity column, Thus, our data s uggest that residues 141 to 160 of the integrin beta(1) subunit, when arranged in an alpha-helix configuration, participate in ligand bindin g.