Integrin alpha-5
calcium ion binding
Structural insights into integrin α<sub>5</sub>β<sub>1</sub> opening by fibronectin ligand.
Integrin α<sub>5</sub>β<sub>1</sub> is a major fibronectin receptor critical for cell migration. Upon complex formation, fibronectin and α<sub>5</sub>β<sub>1</sub> undergo conformational changes. While this is key for cell-tissue connections, its mechanism is unknown. Here, we report cryo-electron microscopy structures of native human α<sub>5</sub>β<sub>1</sub> with fibronectin to 3.1-angstrom resolution, and in its resting state to 4.6-angstrom resolution. The α<sub>5</sub>β<sub>1</sub>-fibronectin complex revealed simultaneous interactions at the arginine-glycine-aspartate loop, the synergy site, and a newly identified binding site proximal to adjacent to metal ion-dependent adhesion site, inducing the translocation of helix α1 to secure integrin opening. Resting α<sub>5</sub>β<sub>1</sub> adopts an incompletely bent conformation, challenging the model of integrin sharp bending inhibiting ligand binding. Our biochemical and structural analyses showed that affinity of α<sub>5</sub>β<sub>1</sub> for fibronectin is increased with manganese ions (Mn<sup>2+</sup>) while adopting the half-bent conformation, indicating that ligand-binding affinity does not depend on conformation, and α<sub>5</sub>β<sub>1</sub> opening is induced by ligand-binding.