PSAP (Prosaposin, SAP1) is a preproprotein that is proteolytically processed to generate saposins A, B, C, and D. Saposins localize to lysosomes where they catabolize glycosphingolipids with short oligosaccharide groups. The precursor exists as both a secretory and integral membrane protein. The secretory prosaposin promotes protective effects in the nervous system by activating G proteins, including GPR37 and GPR37L1. Mutations in PSAP are associated with Gaucher disease and metachromatic leukodystrophy. The protein is expressed in all tissues. References: Brain Res 2014 1585:1; Am J Med Genet 2009 149A(4):613; Mol Genet Metab 2012 106(3):257