Abstract
Integrin receptors bind collagen via metal-mediated interactions that are modulated by magnesium (Mg(2+)) levels in the extracellular matrix. Nuclear magnetic resonance-based relaxation experiments, isothermal titration calorimetry, and adhesion assays reveal that Mg(2+) functions as both a structural anchor and dynamic switch of the α(1)β(1) integrin I domain (α(1)I). Specifically, Mg(2+) binding activates micro- to millisecond timescale motions of residues distal to the binding site, particularly those surrounding the salt bridge at helix 7 and near the metal ion-dependent adhesion site. Mutagenesis of these residues impacts α(1)I functional activity, thereby suggesting that Mg-bound α(1)I dynamics are important for collagen binding and consequent allosteric rearrangement of the low-affinity closed to high-affinity open conformation. We propose a multistep recognition mechanism for α(1)I-Mg-collagen interactions involving both conformational selection and induced-fit processes. Our findings unravel the multifaceted role of Mg(2+) in integrin-collagen recognition and assist in elucidating the molecular mechanisms by which metals regulate protein-protein interactions.