Role of the αI domain in ligand binding by integrin αEβ7

The I domain of integrin αE was modeled on the crystal structure of that in CD11b and mutated to produce an open (high affinity) or closed (low affinity) conformation. K562 transfectants expressing mutant αE and wild‐type β7 were tested for adhesion to E‐cadherin‐Fc. Downward displacement of the C terminus of the αI domain with a disulfide bridge enhanced adhesion and Mn2+ dependency. Adhesion greatly exceeded that observed using wild type integrin under similar conditions. The closed integrin gave poor adhesion which was greatly improved by PMA‐induced clustering. Blocking β7 function with a βI domain‐specific antibody inhibited the wild‐type but not the locked open integrin. Isolated open αI domain expressed on K562 cells showed strong Mn2+‐dependent adhesion to E‐cadherin, whereas the wild‐type version was ineffective. αEβ7 was shown to bind to monomeric E‐cadherin but to only one component of dimeric E‐cadherin. Finally, we report that M290, a function‐blocking antibody, bound to a conformation‐sensitive epitope near the rim of the αI domain MIDAS and recognized wild‐type and closed αI domain but not the open conformation. The results broadly support the paradigm for affinity regulation by conformational change that has been established for β2 integrins. Nevertheless, for αE, the fully open conformation may represent an extreme situation that does not occur physiologically.