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 to 69 of saposin B. The circul ar dichroism spectrum of sapB-18 at pH 4.4 was consistent with a 44% a lpha-helix content. As shown by intrinsic Tyr fluorescence studies of sapB-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 residues 52 and 69 of saposin B plays a major role in the recognition and binding of GM1-ganglioside by saposin B.