Figure 1.

Schematic representation of DPP4 modular structure. Human CD26/DPP4 is a type 2 transmembrane serine protease comprising 766 amino acids (aa). The extracellular catalytic region (Cat, aa 506–766) with the catalytic triad H₇₄₀, N₇₀₈, and S₆₃₀ is located at the C-terminus followed by a cysteine-rich region (Cys, aa 351–497), a glycosylated region (Glyc, aa 101–350), another short cysteine-rich region (Cys, aa 55–100), and a flexible stalk region (aa 30-48). The transmembrane domain (TM) encompasses aa 17–29 and only 6 amino acids constitute the N-terminal cytosolic (Cyt) part of the molecule. The extracellular part contains binding sites for interaction partners like adenosine deaminase (aa 340–343) or fibronectin (aa 469–479). Full-length CD26/DPP4 is suggested to be cleaved within its flexible stalk region to release catalytically active soluble CD26/DPP4 (figure adapted from [1]).