Dissociation of the α-subunit Calf-2 domain and the β-subunit I-EGF4 domain in integrin activation and signaling.

Integrin conformational changes mediate integrin activation and signaling triggered by intracellular molecules or extracellular ligands. Even though it is known that αβ transmembrane domain separation is required for integrin signaling, it is still not clear how this signal is transmitted from the transmembrane domain through two long extracellular legs to the ligand-binding headpiece. This study addresses whether the separation of the membrane-proximal extracellular αβ legs is critical for integrin activation and outside-in signaling. Using a disulfide bond to restrict dissociation of the α-subunit Calf-2 domain and β-subunit I-EGF4 domain, we were able to abolish integrin inside-out activation and outside-in signaling. In contrast, disrupting the interface by introducing a glycosylation site into either subunit activated integrins for ligand binding through a global conformational change. Our results suggest that the interface of the Calf-2 domain and the I-EGF4 domain is critical for integrin bidirectional signaling.