IDENTIFICATION OF A NOVEL INTEGRIN BINDING-SITE IN FIBRONECTIN - DIFFERENTIAL UTILIZATION BY BETA-3 INTEGRINS

Fibronectin (Fn) binding to the integrins alpha IIb beta 3 and alpha v beta 3 involves the Arg-Gly-Asp sequence. The identification of other regions of Fn that interact with alpha IIb beta 3 suggests a potentia l mechanism for differential ligand recognition by integrins. We repor t here the identification of an 11-residue peptide sequence from the 9 th type III repeat of Fn (3Fn9), which inhibits ligand binding to alph a IIb beta 3 by interacting directly with this receptor. Mutational an alysis demonstrated that this same region was involved in the formatio n of epitopes for two anti-Fn mAbs that inhibit Fn binding to alpha II b beta 3, thus emphasizing the role of this site in the macromolecule. Molecular modeling of the 3Fn9-10 modules suggested that Fn residues Asp(1373)-Th-1383 are at least 25 Angstrom distant from the Arg-Gly-As p site and therefore does not directly interact with it. The 3Fn9 site was differentially recognized by the beta 3 integrin family. The Asp( 1373)-Thr(1383) peptide failed to inhibit ligand binding to alpha v be ta 3, a recombinant Fn Ala(1235)-Ser(1436) fragment was not recognized by alpha v beta 3, and addition of the 3Fn9 module to the amino termi nus of the 3Fn10 did not affect the potency of inhibiton of Fn binding to alpha v beta 3. Thus, a novel integrin recognition site in the 3Fn 9 module of Fn that is differentially recognized by the beta 3 integri ns has been localized within the residues Asp(1373)-Thr(1383).