Changed interface between TM domains by cytosolic adaptors during inside-out signaling. The heterodimeric (α/β) integrins belong to a family of 24 members composed of different α/β subunit combinations. Each subunit consists of a large extracellular ligand-binding domain (ectodomain), a single transmembrane domain, and a small cytoplasmic tail of ∼20 to 70 residues. (A) Comparison of 2 different models of inactive integrin. (Top panel) Overall topology of integrin αIIbβ3 ectodomain based on crystallographic information. The ligand-binding head piece points down toward the membrane. αIIb is colored in blue and β3 in red. (Bottom panel) Overall topology of intact integrin αIIbβ3 based on the EM study.1 Yellow arrows indicate the ligand-binding site. (B) A modified switchblade conformational transition model for integrin activation. See Figure 4 in the article by Choi et al that begins on page 4165.
