Dynamic structural changes are observed upon collagen and metal ion binding to the integrin α1 I domain.

Paul H Weinreb, Sheng Li, Sharon X Gao, Tong Liu, R Blake Pepinsky, Justin A Caravella, Jun H Lee, Virgil L Woods

The Journal of biological chemistry 2012 Sep 21

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We have applied hydrogen-deuterium exchange mass spectrometry, in conjunction with differential scanning calorimetry and protein stability analysis, to examine solution dynamics of the integrin α1 I domain induced by the binding of divalent cations, full-length type IV collagen, or a function-blocking monoclonal antibody. These studies revealed features of integrin activation and α1I-ligand complexes that were not detected by static crystallographic data. Mg(2+) and Mn(2+) stabilized α1I but differed in their effects on exchange rates in the αC helix. Ca(2+) impacted α1I conformational dynamics without altering its gross thermal stability. Interaction with collagen affected the exchange rates in just one of three metal ion-dependent adhesion site (MIDAS) loops, suggesting that MIDAS loop 2 plays a primary role in mediating ligand binding. Collagen also induced changes consistent with increased unfolding in both the αC and allosteric C-terminal helices of α1I. The antibody AQC2, which binds to α1I in a ligand-mimetic manner, also reduced exchange in MIDAS loop 2 and increased exchange in αC, but it did not impact the C-terminal region. This is the first study to directly demonstrate the conformational changes induced upon binding of an integrin I domain to a full-length collagen ligand, and it demonstrates the utility of the deuterium exchange mass spectrometry method to study the solution dynamics of integrin/ligand and integrin/metal ion interactions. Based on the ligand and metal ion binding data, we propose a model for collagen-binding integrin activation that explains the differing abilities of Mg(2+), Mn(2+), and Ca(2+) to activate I domain-containing integrins.

Citation

Paul H Weinreb, Sheng Li, Sharon X Gao, Tong Liu, R Blake Pepinsky, Justin A Caravella, Jun H Lee, Virgil L Woods. Dynamic structural changes are observed upon collagen and metal ion binding to the integrin α1 I domain. The Journal of biological chemistry. 2012 Sep 21;287(39):32897-912