Figure 2.

Maturation of the cellular protease furin. Furin expression is driven by three different promoters, sharing characteristics of either cytokine‐activated (P1) or housekeeping gene (P1A and P1B) promoters. During translation, furin is integrated into ER membranes and glycosylated. After the N‐terminal signal peptide (red) is removed, an autocatalytic cleavage event occurs, generating a short propeptide (light blue). This propeptide remains associated with furin and acts as an intramolecular chaperone and inhibitor. After transit to the Golgi complex, the propeptide is removed and glycans are trimmed before furin gains its proteolytic activity. Furin accumulates in the trans‐Golgi network (TGN), but can also traffic to the plasma membrane and cycle between these two compartments via endosomes. Proteolytic cleavage at the C terminus of furin separates the transmembrane domain (orange) from the catalytically active domain. As a result, furin can be shed into the extracellular space as an active enzyme.