Fig. 2.

The existing conformations of the β₂ integrins and the proposed consequences of conformational changes. (A) The resting state of β₂ integrin has bent ectodomain with closed headpiece. (B) The resting β₂ integrin can extend its ectodomain. This conformation may have intermediate affinity to the ligand and mediate leukocyte slow rolling. (C) Further conformational changes can induce headpiece-opening and acquire fully activated β₂ integrin. This conformation has high affinity to the ligands and is thought to support arrest and leukocyte adhesion. (D) The structure of bent ectodomain with open headpiece was also crystallized in β₂ integrin.