STRUCTURAL STUDY OF THE OLIGOSACCHARIDE MOIETIES OF SPHINGOLIPID ACTIVATOR PROTEINS, SAPOSIN-A, SAPOSIN-C AND SAPOSIN-D OBTAINED FROM THE SPLEEN OF A GAUCHER PATIENT

We have determined and compared the structures of the oligosaccharide moieties of saposin A, C and D purified from the spleen of a patient with Gaucher disease. These saposins, together with saposin B, are small glycoproteins, derived from separate domains of a single precursor, prosaposin, and are required for the lysosomal hydrolysis of various sphingolipids. The characteristic features of the oligosaccharide moieties of saposin A are (a) the predominance of a fucosylated trimannosyl core structure and (b) the occurrence of several different oligomannose-type and N-acetyllactosamine-type oligosaccharides. Saposin C contains (a) a predominance of oligomannose-type oligosaccharides and monoantennary oligosaccharides and (b) the presence of four different oligosaccharides having bisecting N-acetylglucosamine residues (found only in this saposin). Saposin D is distinguished by the occurrence of oligomannose-type oligosaccharides, which comprise nearly 90% of its total oligosaccharides. The possible reasons for the unique glycosylation of each saposin is discussed.