InterPro domain: IPR011001

The lysosomal degradation of several sphingolipids requires the presence of four small glycoproteins called saposins, generated by proteolytic processing of a common precursor, prosaposin [ 1 ]. Saposins have three conserved disulphide bridges, and display a 5-helical, closed, folded leaf topology. Other proteins have been shown to have structures that closely resemble saposin, such as the antimicrobial peptides NK-lysin and granulysin [ 2 , 3 ]. Some proteins contain saposin-like domains, such as prophytepsin, an acid protease from plants, and J3-crystallin, an eye-lens protein from jellyfish, both of which contain circularly permuted saposin motifs called swaposin [ 4 , 5 ]. In some saposins and saposin-like domains, lipid-binding can promote conformational changes and oligomerization.

1. Saposins and their interaction with lipids. Neurochem. Res. 24, 307-14
2. NK-lysin, structure and function of a novel effector molecule of porcine T and NK cells. Vet. Immunol. Immunopathol. 54, 123-6
3. Granulysin. Curr. Opin. Immunol. 15, 560-5
4. Crystal structure of plant aspartic proteinase prophytepsin: inactivation and vacuolar targeting. EMBO J. 18, 3947-55
5. J3-crystallin of the jellyfish lens: similarity to saposins. Proc. Natl. Acad. Sci. U.S.A. 98, 12362-7