PMID: 23798730

Authors:

Zhu J, Zhu J, Springer TA

Title:

Complete integrin headpiece opening in eight steps.

Journal:

J Cell Biol. 2013 Jun 24;201(7):1053-68. doi: 10.1083/jcb.201212037.

Abstract:

Carefully soaking crystals with Arg-Gly-Asp (RGD) peptides, we captured eight distinct RGD-bound conformations of the alphaIIbbeta3 integrin headpiece. Starting from the closed betaI domain conformation, we saw six intermediate betaI conformations and finally the fully open betaI with the hybrid domain swung out in the crystal lattice. The beta1-alpha1 backbone that hydrogen bonds to the Asp side chain of RGD was the first element to move followed by adjacent to metal ion-dependent adhesion site Ca(2+), alpha1 helix, alpha1' helix, beta6-alpha7 loop, alpha7 helix, and hybrid domain. We define in atomic detail how conformational change was transmitted over long distances in integrins, 40 A from the ligand binding site to the opposite end of the betaI domain and 80 A to the far end of the hybrid domain. During these movements, RGD slid in its binding groove toward alphaIIb, and its Arg side chain became ordered. RGD concentration requirements in soaking suggested a >200-fold higher affinity after opening. The thermodynamic cycle shows how higher affinity pays the energetic cost of opening.