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[摘要]：Integrin bidirectional signaling is mediated by conformational change. It has been shown that the separation of the alpha- and beta-subunit transmembrane/cytoplasmic tails and the lower legs is required for transmitting integrin bidirectional signals across the plasma membrane. In this study, we address whether the separation of the alpha beta knee is critical for integrin activation and outside-in signaling. By introducing three disulfide bonds to restrict dissociation of the alpha-subunit thigh domain and beta-subunit I-EGF2 domain, we found that two of them could completely abolish integrin inside-out activation, whereas the other could not. This disulfide-bonded mutant, in the context of the activation mutation of the cytoplasmic domain, had intermediate affinity for ligands and was able to mediate cell adhesion. Our data suggest that there exists rearrangement at the interface between the thigh domain and the I-EGF2 domain during integrin inside-out activation. None of the disulfide-bonded mutants could mediate cell spreading upon adhering to immobilized ligands, suggesting that dissociation of the integrin two knees is required for integrin outside-in signaling. Disrupting the interface by introducing a glycan chain into either subunit is sufficient for high affinity ligand binding and cell spreading. |
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