The GNPTG gene codes instructions for making the gamma subunit of an enzyme called GlcNAc-1-phosphotransferase (also called N-acetylglucosamine-1-phosphate transferase). This enzyme is made up of two alpha (α), two beta (β), and two gamma (γ) subunits. GNPTAB produces the alpha and beta subunits. GlcNAc-1-phosphotransferase functions to prepare newly made enzymes for lysosome transportation (lysosomal hydrolases to the lysosome). Lysosomes, a part of an animal cells, helps break down large molecules into smaller ones that can be reused. GlcNAc-1-phosphotransferase catalyzes the N-linked glycosylation of asparagine residues with a molecule called mannose-6-phosphate (M6P). M6P acts as indicator whether a hydrolase should be transported to the lysosome or not. Once a hydrolase has the indication from an M6P, it can be transported to a lysosome.
