Magnesium Activates Microsecond Dynamics to Regulate Integrin-Collagen Recognition.

Integrin receptors bind collagen via metal-mediated interactions that are modulated by magnesium (Mg2+) levels in the extracellular matrix. Nuclear magnetic resonance-based relaxation experiments, isothermal titration calorimetry, and adhesion assays reveal that Mg2+ functions as both a structural anchor and dynamic switch of the α1β1 integrin I domain (α1I). Specifically, Mg2+ 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 α1I functional activity, thereby suggesting that Mg-bound α1I 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 α1I-Mg-collagen interactions involving both conformational selection and induced-fit processes. Our findings unravel the multifaceted role of Mg2+ in integrin-collagen recognition and assist in elucidating the molecular mechanisms by which metals regulate protein-protein interactions.