TAILIEUCHUNG - Báo cáo khoa học: Saposin B mobilizes lipids from cholesterol-poor and bis(monoacylglycero)phosphate-rich membranes at acidic pH

Sphingolipid activator proteins (SAPs), GM2 activator protein (GM2AP) and saposins (Saps) A–D are small, enzymatically inactive glycoproteins of the lysosome. Despite of their sequence homology, these lipid-binding and -transfer proteins show different specificities and varying modes of action. Water-soluble SAPs facilitate the degradation of membrane-bound glyco-sphingolipids with short oligosaccharide chains by exohydrolases at the membrane–water interface. | ỊFEBS Journal Saposin B mobilizes lipids from cholesterol-poor and bis monoacylglycero phosphate-rich membranes at acidic pH Unglycosylated patient variant saposin B lacks lipid-extraction capacity Natascha Remmel Silvia Locatelli-Hoops Bernadette Breiden Guenter Schwarzmann and Konrad Sandhoff LIMES Membrane Biology Lipid Biochemistry Unit c o Kekule-Institut fur Organische Chemie und Biochemie University of Bonn Germany Keywords glycosphingolipid lipid-binding protein lysosome Sap saposin Correspondence K. Sandhoff LIMES Membrane Biology Lipid Biochemistry Unit c o Kekule-Institut fur Organische Chemie und Biochemie Gerhard-Domagk-Strasse 1 53121 Bonn Germany Fax 49 228 737 778 Tel 49 228 735 346 E-mail sandhoff@ Received 8 February 2007 revised 26 April 2007 accepted 8 May 2007 doi Sphingolipid activator proteins SAPs GM2 activator protein GM2AP and saposins Saps A-D are small enzymatically inactive glycoproteins of the lysosome. Despite of their sequence homology these lipid-binding and -transfer proteins show different specificities and varying modes of action. Water-soluble SAPs facilitate the degradation of membrane-bound glycosphingolipids with short oligosaccharide chains by exohydrolases at the membrane-water interface. There is strong evidence that degradation of endocytosed components of the cell membrane takes place at intraendo-somal and intralysosomal membranes. The inner membranes of the lysosome differ from the limiting membrane of the organelle in some typical ways the inner vesicular membranes lack a protecting glycocalix and they are almost free of cholesterol but rich in bis monoacylglycero phosphate BMP the anionic marker lipid of lysosomes. In this study we prepared glycosylated Sap-B free of other Saps by taking advantage of the Pichia pastoris expression system. We used immobilized liposomes as a model for intralysosomal vesicular membranes to probe their interaction with rec-ombinantly expressed

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