IDENTIFICATION OF A SPECIES-SPECIFIC INHIBITOR OF GLYCOSYLPHOSPHATIDYLINOSITOL SYNTHESIS

Glycosylphosphatidylinositol (GPI)-anchoring represents a mechanism fo r attaching proteins to the cell surface that is used among all eukary otes, A common core structure, EthN-P-Man(3)-GlcN-PI, is synthesized b y sequential transfer of sugars and ethanolamine-P to PI and is highly conserved between organisms. We have screened for natural compounds t hat inhibit GPI-anchoring in yeast and have identified a terpenoid lac tone, YW3548, that specifically blocks the addition of the third manno se to the intermediate structure Man(2)-GlcN-acylPI. Consistent with t he block in GPI synthesis. YW3548 prevents the incorporation of [H-3]m yo-inositol into proteins, transport of GPI-anchored proteins to the G olgi and is toxic. The compound inhibits the same step of GPI synthesi s in mammalian cells, but has no significant activity in protozoa. The se results suggest that despite the conserved core structure, the GPI biosynthetic machinery may be different enough between mammalian and p rotozoa to represent a target for anti-protozoan chemotherapy.