Expression of a structural domain of the β 2 subunit essential for α M β 2 ligand recognition

The β 2 leukocyte integrins comprise a group of closely related adhesion receptors that mediate critical events during normal and inflammatory immune responses. Central to the understanding of β 2 integrin function is the basis of ligand recognition. Results from our laboratory and others indicate the presence of multiple ligand contact points in both the α and β subunit. As an approach to identify and characterize regulatory domains of the β 2 subunit, we have generated two different subdomains of the β 2 subunit for expression on the surface of mammalian cells through a phosphatidylinositol glycan anchor. The first subdomain contains the putative β 2 MIDAS motif implicated in ligand binding [β 2 (LB)], whereas the second β 2 subdomain contains the cysteine‐rich region [β 2 (CR)]. Cells expressing α m and β 2 constructs singly or cotransfected transiently in COS‐7 cells were tested for the ability to bind to immobilized iC3b. Cells bearing the recombinant α M β 2 (LB) were capable of adhering to iC3b in a manner similar to that observed with the complete α M β 2 heterodimer. In contrast, cells expressing α M β 2 (CR) failed to adhere to immobilized iC3b. Moreover, cells bearing singly transfected α or β chains alone failed to adhere to immobilized iC3b. These results indicate that along with α m , the β 2 (LB) subdomain contains the sufficient components within the β 2 subunit essential for ligand recognition. These findings support the hypothesis that the β 2 subunit cooperates with site(s) within the α M subunit in a receptor/cation/ligand complex resulting in high‐affinity ligand interaction. J. Leukoc. Biol. 64: 767–773; 1998.