Structural insights into integrin alpha(5)beta(1) opening by fibronectin ligand

Integrin alpha(5)beta(1) is a major fibronectin receptor critical for cell migration. Upon complex formation, fibronectin and alpha(5)beta(1) 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 alpha(5)beta(1) with fibronectin to 3.1-angstrom resolution, and in its resting state to 4.6-angstrom resolution. The alpha(5)beta(1)-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 alpha 1 to secure integrin opening. Resting alpha(5)beta(1) adopts an incompletely bent conformation, challenging the model of integrin sharp bending inhibiting ligand binding. Our biochemical and structural analyses showed that affinity of alpha(5) for fibronectin is increased with manganese ions (Mn2+) while adopting the half-bent conformation, indicating that ligand-binding affinity does not depend on conformation, and alpha(5)beta(1) opening is induced by ligand-binding