PSAP is a highly conserved glycoprotein which is a precursor for 4 cleavage products: saposins A, B, C, and D, which are similar to each other and are sphingolipid hydrolase activator proteins. Each domain of the precursor protein is approximately 80 amino acid residues long with nearly identical placement of cysteine residues and glycosylation sites. Saposins A-D localize primarily to the lysosomal compartment where they facilitate the catabolism of glycosphingolipids with short oligosaccharide groups. The precursor protein exists both as a secretory protein and as an integral membrane protein and has neurotrophic activities. Mutations in PSAP gene have been associated with Gaucher disease, Tay-Sachs disease, and metachromatic leukodystrophy.