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The affinity of the extracellular domain of integrins for ligand is regulated by conformational changes signaled from the cytoplasm. Alternative types of conformational movement in the ligandbinding headpiece have been proposed. In one study, electron micrograph image averages of the headpiece of integrin aVβ3 show two different conformations. The open conformation of the headpiece is present when a ligand mimetic peptide is bound and differs from the closed conformation in the presence of an obtuse angle between the β3 subunit hybrid and I-like domains. We tested the hypothesis that opening of the hybrid-I-like domain interface increases ligand-binding affinity by mutationally introducing an N-glycosylation site into it. Both β3 and β1 integrin glycan wedge mutants exhibit constitutively high affinity for physiological ligands. The data uniquely support one model of integrin activation and suggest that movement at the interface with the hybrid domain pulls down the C-terminal helix of the I-like domain and activates its metal ion-dependent adhesion site, analogously to activation of the integrin I domain.

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Proceedings of the National Academy of Sciences of the United States of America

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