BINDING OF GM1-GANGLIOSIDE TO A SYNTHETIC PEPTIDE DERIVED FROM THE LYSOSOMAL SPHINGOLIPID ACTIVATOR PROTEIN SAPOSIN-B

Saposin B is a lysosomal sphingolipid activator protein which activate s GM1 ganglioside hydrolysis by lysosomal beta-galactosidase. To ident ify the structural elements of saposin B implicated in sphingolipid bi nding, we studied a synthetic peptide corresponding to a predicted alp ha-helix, sapB-18, spanning residues 52-69 of saposin B. The circular dichroism spectrum of sapB-18 at pH 4.4 was consistent with a 44% alph a-helix content. As shown by intrinsic Tyr fluorescence studies of sap B-18, this peptide binds the GM1 ganglioside with a K-d of about 7 mu M. Thus, we suggest that a putative amphipathic alpha-helix between re sidues 52 and 69 of saposin B plays a major role in the recognition an d binding of GM1 ganglioside by saposin B.