LC-MS/MS analysis of soluble lysosomal enzymes

Mucolipidosis III gamma (MLIII) is clinically characterized by onset of first symptoms at an average of 5 years such as stiffness of hands and shoulders, claw hand deformities, scoliosis and progressive destruction of hip joints. The disease is caused by mutations in GNPTG encoding the gamma-subunit of the GlcNAc-1-phosphotransferase complex. This enzyme is responsible for the generation of mannose 6-phosphate (M6P) targeting signals on 70 soluble lysosomal enzymes that are required for their efficient receptor-mediated transport to lysosomes. Complementary SILAC-based lysosomal proteomics revealed decreased amounts of several lysosomal enzymes in Gnptg-KO fibroblasts involved in the degradation of lipids, glycans and proteins.