Complexing of Glycolipids and Their Transfer between Membranes by the Activator Protein for Degradation of Lysosomal Ganglioside GM2

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Abstract
The lysosomal degradation of ganglioside GMZ by hexosaminidase A depends on the presence of the specific activator protein which mediates the interaction between micellar or membrane-bound ganglioside and water-soluble hydrolase. The mechanism and the glycolipid specificity of this activator were studied in more detail. 1 It could be shown with three different techniques (isoelectric focusing, centrifugation and electrophoresis) that the activator protein extracts glycolipid monomers from micelles or liposomes to give water-soluble complexes with a stoichiometry of 1 mol of glycolipid/mol of activator protein. Liposome-bound ganglioside Gm2 is considerably more stable against extraction and degradation than micellar ganglioside. 2 In the absence of enzyme the activator acts in vitro as glycolipid transfer protein, transporting glycolipids from donor to acceptor membranes. 3 The activator protein is rathcr specific for ganglioside GM2. Other glycolipids (GM3, GM1, GDla and GA2) form less stable complexes with the activator and are transferred at a slower rate (except for ganglioside G, than ganglioside GM2.