Fig. 1.

Schematic illustration of lysosomal cathepsin maturation. Cathepsins are initially synthesized as inactive preproenzymes with a N-terminal signal peptide, guiding them through the rough endoplasmic reticulum (RER). The signal peptide is cleaved in the ER lumen, after which they are directed via the mannose-6-phosphate (Man-6-P) receptor pathway to the lysosome through the trans-Golgi network. Procathesins dissociate from the Man-6-P receptor within late endosomes. Finally, Cathepsins undergo auto-catalysis or cleavage by other proteases to attain their mature form