InterPro domain: IPR008138

Saposins are small lysosomal proteins that serve as activators of variouslysosomal lipid-degrading enzymes [ 1 ]. They probably act by isolating thelipid substrate from the membrane surroundings, thus making it more accessible to the soluble degradative enzymes. All mammalian saposinsare synthesized as a single precursor molecule (prosaposin) which containsfour Saposin-B domains, yielding the active saposins after proteolyticcleavage, and two Saposin-A domains that are removed in the activationreaction. The Saposin-B domains also occur in other proteins, many of them active in the lysis of membranes [ 2 , 3 ].

1. Saposin-like proteins (SAPLIP) carry out diverse functions on a common backbone structure. J. Lipid Res. 36, 1653-63
2. Acid sphingomyelinase possesses a domain homologous to its activator proteins: saposins B and D. Protein Sci. 3, 359-61
3. Cytotoxic T cells: more weapons for new targets? Trends Microbiol. 4, 91-4