Binding of cerebrosides and sulfatides to saposins A-D.
Saposins are a family of four small glycoproteins, all of which are derived from prosaposin, and are involved in the lysosomal hydrolysis of various sphingolipids. Results from this investigation demonstrate that saposins A-D bind to galactosyl- and glucosylceramide. The binding was highly dependent on the solution pH; maximum binding of glucosylceramide to all saposins occurred at pH 7. Maximum binding of galactosylceramide to saposins B and D occurred at a more basic pH (8.5). The binding of glucosylceramide to saposins was significantly inhibited by Mg2+, Ca2+, or Zn2+. Although maximum binding of sulfatide to saposins A, C, and D occurred at acidic pH, the binding to saposin B was maximum at pH 8.5. Saposin A also bound sphingomyelin or phosphatidylcholine at neutral pH. No significant binding was evident between these lipids and saposins B-D at any pH value. The existence of saposin-lipid complexes was further confirmed in selected samples by gel filtration, isoelectric focusing, and a TLC binding assay. We have also shown that galactosylceramide bound to saposins A-D was efficiently transported to a rat brain microsomal fraction. This result suggests that saposins and possibly their precursor, prosaposin, may be involved in membrane biogenesis such as the assembly of myelin and plasma membranes.
Soeda
S
S
Department of Neurosciences, University of California, San Diego, La Jolla 92093-0634.
Hiraiwa
M
M
O'Brien
J S
JS
Kishimoto
Y
Y
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002554:Cerebrosides / Q000378:metabolism*; D002855:Chromatography, Thin Layer; D005699:Galactosylceramides / Q000378:metabolism; D005963:Glucosylceramides / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007525:Isoelectric Focusing; D008274:Magnesium / Q000494:pharmacology; D051381:Rats; D049231:Saposins; D049128:Sphingolipid Activator Proteins; D013433:Sulfoglycosphingolipids / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology
D002554:Cerebrosides; D005699:Galactosylceramides; D005963:Glucosylceramides; D006023:Glycoproteins; C483347:Psap protein, rat; D049231:Saposins; D049128:Sphingolipid Activator Proteins; D013433:Sulfoglycosphingolipids; D008274:Magnesium; D015032:Zinc; D002118:Calcium