In the tsetse fly, the surface of Trypanosoma congolense parasites is covered by a dense layer of glycosylphosphatidylinositol (GPI)-anchored molecules. These include EPGENGT procyclin and protease resistant surface molecule (PRS), as well as congolense epimastigote-specific protein, CESP, and glutamic acid- and alanine-rich protein (GARP). The GPI structures of EPGENGT and GARP have been partially elucidated, but very little is known about PRS. We now purified PRS and analyzed its GPI lipid structure and carbohydrate composition using mass spectrometry. We found that unlike EPGENGT and GARP, the GPI anchor of PRS is unusually composed of inositol-acylated diacyl-phosphatidylinositols, including species containing either myristic or oleic acid at the sn-2 position of the glycerol backbone. This is the first identification of a tri-acylated GPI anchor containing myristate in procyclic form trypanosomes. In addition, we found that PRS is highly rich in galactose and sialic acid residues, suggesting that it may represent a major acceptor of the parasite trans-sialidase.
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