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Integrins are heterodimeric transmembrane proteins that play important roles in various biological processes. Most integrins serve as adhesion molecules and transmit bidirectional signaling across the cell membrane through global conformational changes from the bent closed to the extended open conformation. However, integrin β8 is distinctive in structure and function. Its cytoplasmic domain lacks the conserved protein‐binding sequence, which is important in transmitting inside‐out signals, suggesting that integrin β8 may have a different activation mechanism or lack such signaling. In addition, the ligand‐binding or activating metal ion Mn2+ does not induce a global conformational change in integrin β8. It may have only one conformation, that is, an extended, closed conformation, but with high affinity for ligands under physiological conditions, and is, therefore, considered an atypical integrin member. The extended structure and high ligand‐binding affinity of integrin αvβ8 make it ideal for encountering and binding ligands expressed on an opposing cell or in the extracellular matrix. In this review, we summarize the progress in integrin β8 research with a focus on its distinctive function and structure among integrin members. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]