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 alpha(1)beta(1) integrin I domain (alpha I-1). 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 alpha I-1 functional activity, thereby suggesting that Mg-bound alpha I-1 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 alpha I-1-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.