Dipeptidyl peptidase (DPP) family members 8 and 9 are similar to DPP4, consisting of one N-terminal β-propeller and a C-terminal alpha/beta hydrolase domain, which form a functional homodimer. This entry represents the N-terminal β-propeller of DPP8 and 9 which consists of eight blades and enlaces a central round pore. It provides the key arginine residue fundamental for substrate fixation which is located in the R-segment, at the interconnecting loop between blades 1 and 2. Ligand binding to DPP8/9 induces a rearrangement at the active site through a disorder-order transition in a loop segment which includes the key arginine residue and partially folds in an α-helix (R-helix) []. DPP8 and DPP9 play a role in the immune system and in preadipocyte differentiation. DPP9 is also essential for neonatal survival and plays a role in antigen maturation, cell migration, and cell adhesion.
