<p>The lysosomal degradation of several sphingolipids requires the presence of four small glycoproteins called saposins, generated by proteolytic processing of a common precursor, prosaposin [<cite idref="PUB00014080"/>]. 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 [<cite idref="PUB00014081"/>, <cite idref="PUB00014082"/>]. 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 [<cite idref="PUB00014083"/>, <cite idref="PUB00014084"/>]. In some saposins and saposin-like domains, lipid-binding can promote conformational changes and oligomerization.</p>