The β₈ integrin EGF domains support a constitutive extended conformation, and the cytoplasmic domain impairs...

Integrins are transmembrane proteins that transmit bi-directional signals across the cell membrane through global structural rearrangement among three different conformational states: bent, extended- closed, and extended-open conformations. However, the β₈ integrin is distinctive and may adopt only one conformation, that is, extended-closed conformation, with high affinity for ligands under physiological conditions, and may not transmit bi-directional signals like other integrin members. It is unclear how different β₈ domains affect its unique conformation and signaling. We swapped different domains of integrin β₃ with those of β₈ and investigated how they affected integrin ligand binding, global conformation, and outside-in signaling. We found that the β₈ epidermal growth factor (EGF) domains increased integrin ligand binding ability and contributed to its extended conformation. By comparison, the β₈ transmembrane and cytoplasmic domains had little effect on ligand binding or global conformation. The β₈ EGF and transmembrane domains did not affect integrin-mediated cell adhesion, cell spreading, focal adhesion formation, or colocalization of integrin with other proteins, but the cytoplasmic domain had a defective effect on outside-in signaling. Our results showed that different domains of β₈ play various roles on its unique conformation, ligand binding, and signaling, which are considered atypical among integrin members.