The structure was elucidated in this paper NCBI PubMed ID:9593686 Journal NLM ID:2985121R Publisher: Baltimore, MD: American Society for Biochemistry and Molecular Biology Correspondence: thomas.ilgtuebingen.mpg.de Institutions: Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Victoria 3052, Australia, Walter and Eliza Hall Institute of Medical Research, P.O. Royal Melbourne Hospital, Victoria 3050, Australia, the Centre for Drug Design and Development, University of Queensland, Brisbane, Queensland 4072, Australia, Centre for Molecular Biology, Heidelberg, Germany
Intracellular amastigotes of the protozoan parasite Leishmania mexicana secrete a macromolecular proteo-phosphoglycan (aPPG) into the phagolysosome of their host cell, the mammalian macrophage. The structures of aPPG glycans were analyzed by a combination of high pH anion exchange high pressure liquid chromatography, gas chromatography-mass spectrometry, enzymatic digestions, electrospray-mass spectrometry as well as 1H and 31P NMR spectroscopy. Some glycans are identical to oligosaccharides known from Leishmania mexicana promastigote lipophosphoglycan and secreted acid phosphatase. However, the majority of the aPPG glycans represent amastigote stage-specific and novel structures. These include neutral glycans ( [Glc(bl-3)(n=1-2)]Gal(bl-4)Man, Gal(bl-3)Gal(bl-4)Man, Gal(bl-3)Glc(bl-3)Gal(bl-4)Man ), several monophosphorylated glycans containing the conserved phosphodisaccharide backbone (R-3-[PO4-6-Gal] (bl-4)Man) but carrying stage-specific modifications ( R = Gal(bl-,[Glc(bl-3)(n=1-2)Glc(bl- ), and monophosphorylated aPPG tri- and tetrasaccharides that are uniquely phosphorylated on the terminal hexose ( PO4-6-Glc(bl-3)Gal(bl-4)Man, PO4-6-Glc(bl-3)Glc(bl-3)Gal(bl-4)Man, PO4-6-Gal(bl-3)Glc(bl-3)Gal(b1-4)Man ). In addition aPPG contains highly unusual di- and triphosphorylated glycans whose major species are PO4-6-Glc(bl-3)Glc(bl-3)[PO4-6-Gal](bl-4)Man, PO4-6-Gal(bl-3)Glc(b1-3)[PO4-6-Gal](bl-4)Man, PO4-6-Gal(bl-3)Glc(bl-3)Glc(bl-3)[PO4-6-Gal](bl-4)Man, PO4-6-Glc(bl-3)[PO4-6-Glc](bl-3)[PO4-6-Gal](b1-4)Man, PO4-6-Gal(bl-3)[PO4-6-Glc](bl-3)Glc(bl-3)[PO4-6-Gal](bl-4)Man, and PO4-6-Glc(bl-3)[PO4-6-Glc](bl-3)Glc(bl-3)[PO4-6-Gal](bl-4)Man. These glycans are linked together by the conserved phosphodiester R-Man-(a1-PO4-6)-Gal-R or the novel phosphodiester R-Man-(a1-PO4-6)-Glc-R and are connected to Ser(P) of the protein backbone most likely via the linkage R-Man-(a1-PO4-Ser). The variety of stage-specific glycan structures in Leishmania mexicana aPPG suggests the presence of developmentally regulated amastigote glycosyl-transferases which may be potential anti-parasite drug targets.
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