MOLECULAR-SPECIES ANALYSIS AND QUANTIFICATION OF THE GLYCOSYLPHOSPHATIDYLINOSITOL INTERMEDIATE GLYCOLIPID-C FROM TRYPANOSOMA-BRUCEI

The precursor of the glycosylphosphatidylinositol membrane anchor of t he variant surface glycoprotein of Trypanosoma brucei is known as glyc olipid A and it has the structure: EtN-PO4-6Man alpha 1-2Man alpha 1-2 Man alpha 1-6Man alpha 1-4GlcN(alpha -6)myo-inositol1-PO4-(sn-1,2-dimy ristoylglycerol). This precursor exists in equilibrium with its inosit ol-acylated form known as glycolipid C that contains a fatty acid atta ched to the inositol ring. In this study, we describe the purification to homogeneity of glycolipid C, its precise quantification and the an alysis of the molecular species of glycolipid C by electrospray ionisa tion mass spectrometry. The results show that glycolipid C is present at 160 000 copies per cell, that glycolipid C is acylated on the 2-pos ition of the myo-inositol ring and that glycolipid C is heterogeneous with respect to the acyl chain attached to the inositol ring. The impl ications of these results with respect to the nature of the trypanosom e inositol acyltransferase are discussed.