Fig. 2. Integrin activation. An integrin achieves higher affinity for ligand through conformational change or gains strength of binding through clustering (avidity). These two states can be accomplished experimentally through binding of Mg²⁺, Mn²⁺, activating mAbs or treatment with phorbol ester or crosslinking TCR. Gene modification of ADAP, SKAP-55 or Vav-1 (complexed with SLP-76; blue) demonstrates their role in integrin clustering. Calpain, GTPases Rac and Rap1, and the Rap1-binding protein RAPL also participate in integrin clustering. Signalling through chemokine receptors to pertussis-toxin-sensitive G proteins can cause a transient increase in integrin affinity. See text for references.

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