Glycobiology World Congress

Biography

Biography: Konrad Sandhoff

Abstract

Cholesterol and sphingolipids (SLs) are stabilizing compounds of eukaryotic plasma membranes. Together with phospholipids (PLs) they reach luminal vesicles of the endolysosomal compartment as platforms for membrane degradation. A maturation process removes lipids inhibiting lysosomal catabolism from the luminal vesicles. Sphingomyelin (SM) is hydrolyzed by acid sphingomyelinase, facilitating cholesterol export to the cytosol by NPC2 and NPC1. SM and cholesterol poor luminal vesicles then serve as platforms for glycosphingolipid degradation in the lysosomes employing soluble hydrolases, SAPs (sphingolipid activator proteins) and anionic PLs as stimulators. We reconstituted the catabolic proteins on liposomal surfaces, mimicking luminal vesicles of the lysosomes as platforms for SL degradation. Liposomes without anionic PLs and with no net surface charge generated only negligible and physiologically irrelevant catabolic rates even at lysosomal pH values. Incorporation of anionic PLs into the SL-carrying liposomes, however, stimulated the catabolic rate by up to more than an order of magnitude. We now found, that the incorporation of cholesterol or SM into the SL carrying liposomal membranes generated a strong inhibition of ganglioside GM2 hydrolysis and the transfer of membrane lipids between liposomal vesicles by SAPs, even in the presence of anionic phospholipids. Ongoing in vitro studies indicate that PM-stabilizing lipids, i.e. SM and cholesterol, inhibit several steps of lysosomal SL and glycosphingolipid catabolism and also lipid solubilisation as studied by Surface Plasmon Resonance and intervesicular (glyco-) lipid transfer activities of several SAPs and NPC2, even in the presence of activating anionic phospholipids.