<p>Synonym(s):cerebroside sulphate activator, CSAct </p> <p> Saposin B is a small non-enzymatic glycoprotein required for the breakdownof cerebroside sulphates (sulphatides) in lysosomes. Saposin B contains three intramolecular disulphide bridges, exists as a dimer and is remarkably heat, protease, and pH stable. The crystal structure of human saposin B reveals an unusual shell-like dimer consisting of a monolayer of alpha-helices enclosing a large hydrophobic cavity. Although the secondary structure of saposin B is similar to that of the known monomeric members of the saposin-like superfamily, the helices are repacked into a different tertiary arrangement to form the homodimer. A comparison of the two forms of the saposin B dimer suggests that extraction of target lipids from membranes involves a conformational change that facilitates access to the inner cavity [<cite idref="PUB00010538"/>].</p>