CRYSTAL-STRUCTURE OF THE A-DOMAIN FROM THE A-SUBUNIT OF INTEGRIN CR3 (CD11B CD18)/

We have determined the high resolution crystal structure of the A doma in from the a chain of integrin CR3. The domain adopts a classic alpha /beta ''Rossmann'' fold and contains an unusual Mg2+ coordination site at its surface. One of the coordinating ligands is the glutamate side chain from another A domain molecule. We suggest that this site repre sents a general metal ion-dependent adhesion site (MIDAS) for binding protein ligands. We further propose that the beta subunits of integrin s contain a MIDAS motif within a modified A domain. Our crystal struct ure will allow reliable models to be built for other members of the A domain superfamily and should facilitate development of novel adhesion modulatory drugs.