title: Dynamic structural changes are observed upon collagen and metal ion binding to the integrin α1 I domain.
abstract: 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.
authors: Biogen Idec, Inc., Cambridge, Massachusetts 02142, USA. paul.weinreb@biogenidec.com
authors: Paul H
authors: PH
authors: Weinreb
authors: Sheng
authors: S
authors: Li
authors: Sharon X
authors: SX
authors: Gao
authors: Tong
authors: T
authors: Liu
authors: R Blake
authors: RB
authors: Pepinsky
authors: Justin A
authors: JA
authors: Caravella
authors: Jun H
authors: JH
authors: Lee
authors: Virgil L
authors: VL
authors: Woods
mesh_terms: D000818:Animals; D024141:Collagen Type IV / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D039423:Integrin alpha1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism*; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats
chemical_list: D024141:Collagen Type IV; D039423:Integrin alpha1; D008345:Manganese; D008274:Magnesium