Globular domain structures of α and β subunits in a stable dimer. This contains a metal-ion dependent adhesion site (MIDAS) which is important for ligand binding. An additional αI (interactive) domain containing ~200 residues is present in some vertebrate α chains (nine human α subtypes) between the propeller repeats 2 and 3. Some of the propeller blade domains contain calcium binding EF-hand domains on the lower side these allosterically affect ligand binding. The α subunit leg consists of a thigh and 2 calf domains that support the ligand binding head formed by a β-propeller domain with 7 repeats forming the blades (shown as a cylinder in the figure below). The α and β groups show no homology to each other,however, conserved regions are found among subtypes of both groups. The αI domain is present in some subtypes of the α subunit.Įach integrin heterodimer consists of an alpha (α) and a beta (β) subunit associated by noncovalent interactions forming an extracellular ligand-binding head, two multi-domain `legs’, two single-pass transmembrane helices and two short cytoplasmic tails. Bottom: simplified version of the integrin α subunit. Middle: The globular structure formed by protein domains. Integrin α subunit domains: Top: Linear domain arrangement.
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