Complete integrin headpiece opening in eight steps. Academic Article uri icon

abstract

  • Carefully soaking crystals with Arg-Gly-Asp (RGD) peptides, we captured eight distinct RGD-bound conformations of the ?IIb?3 integrin headpiece. Starting from the closed ?I domain conformation, we saw six intermediate ?I conformations and finally the fully open ?I with the hybrid domain swung out in the crystal lattice. The ?1-?1 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+), ?1 helix, ?1' helix, ?6-?7 loop, ?7 helix, and hybrid domain. We define in atomic detail how conformational change was transmitted over long distances in integrins, 40 Å from the ligand binding site to the opposite end of the ?I domain and 80 Å to the far end of the hybrid domain. During these movements, RGD slid in its binding groove toward ?IIb, 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.

publication date

  • June 24, 2013