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The structure of Leishmania major amastigote lipophosphoglycan
S F Moody1, E Handman, M J McConville
1Walter and Eliza Hall Institute of Medical Research, Immunoparasitology Unit, Royal Melbourne Hospital, Victoria, Australia.
Abstract:
Intracellular amastigotes of Leishmania major produce 6 x 10(4) copies/cell of a lipophosphoglycan (LPG) that is structurally distinct from the LPG produced by the extracellular promastigote form of L. major, Leishmania donovani, and Leishmania mexicana (reviewed by McConville, M. J. (1991) Cell Biol. Int. Rep. 15, 779-798). L. major amastigote LPG is composed of a lysoalkyl phosphatidylinositol lipid anchor that links via a diphosphorylated hexasaccharide core to a phosphoglycan (6-100 kDa). The structures of the anchor, the core, and the phosphoglycan were determined by monosaccharide and linkage analysis, fast atom bombardment-mass spectrometry, one-dimensional 1H NMR spectroscopy, and exoglycosidase microsequencing. The lipid anchor contains predominantly 1-O-alkylglycerols with 24:0 and 22:0 alkyl chains. The lipids are linked via a glycerol-myo-inositol-PO4 to a core glycan with the structure -PO4-6)Gal(alpha 1-)Gal(alpha 1-) Galf(beta 1-)[Glc(alpha 1-PO4-)]Man(alpha 1-)Man(alpha 1-)GlcN(alpha 1-). The chromatographic characteristics of the core glycan suggest that the saccharide components are linked similarly in amastigote and promastigote LPG. The phosphoglycan attached to the core consists of -PO4-6)Gal(beta 1-4)Man(alpha 1- repeats units which are either unsubstituted (70%) or substituted (30%) at the 3-position of the Gal residues with oligosaccharide side chains containing primarily Gal and some Glc. Thirteen different types of side chains were identified with the structures [Gal(beta 1-3)]x, where x = 1-11, or Glc(1-3)Glc(1-3), or Glc(1-3)Gal(beta 1-3), where glucose is probably in the beta-configuration. All monosaccharides in the phosphoglycan domain are in the pyranose configuration. The average number of repeat units per molecule is 36. The nonreducing terminus of the phosphoglycan chains probably terminates predominantly in the neutral disaccharide Gal(beta 1-4)Man(alpha 1-. Comparison of the structure of L. major amastigote LPG to L. major promastigote procyclic and metacyclic LPG forms (McConville, M. J., Turco, S. J., Furguson, M. A. J., and Sacks, D. L. (1992) Embo J. 11, 3593-3600) indicates that this molecule is developmentally modified throughout the different stages of the parasites' life cycle.
Insights
Intracellular Leishmania major amastigotes produce a distinct lipophosphoglycan (LPG). This LPG has a unique structure, differing from other Leishmania forms, indicating developmental modification during the parasite
Area of Science:
- Parasitology
- Biochemistry
- Molecular Biology
Background:
- Leishmania parasites exhibit distinct life cycle stages, including intracellular amastigotes and extracellular promastigotes.
- Lipophosphoglycan (LPG) is a major surface glycoconjugate in Leishmania, crucial for parasite-host interactions.
- Structural variations in LPG across different Leishmania species and life cycle stages suggest stage-specific functions.
Purpose of the Study:
- To elucidate the detailed structure of lipophosphoglycan (LPG) produced by intracellular amastigotes of Leishmania major.
- To compare the amastigote LPG structure with that of promastigote forms to understand developmental modifications.
- To identify the specific molecular components and linkages within the amastigote LPG.
Main Methods:
- Monosaccharide and linkage analysis
- Fast atom bombardment-mass spectrometry (FAB-MS)
- One-dimensional proton nuclear magnetic resonance (1D 1H NMR) spectroscopy
- Exoglycosidase microsequencing
Main Results:
- Leishmania major amastigote LPG possesses a distinct structure compared to promastigote LPG.
- The LPG comprises a lysoalkyl phosphatidylinositol lipid anchor, a diphosphorylated hexasaccharide core, and a phosphoglycan domain (6-100 kDa).
- The phosphoglycan consists of repeating Gal(β1-4)Man(α1-) units, with 30% substituted with diverse oligosaccharide side chains.
Conclusions:
- Leishmania major amastigote LPG structure is developmentally regulated and differs significantly from promastigote LPG.
- The identified structural features provide insights into the functional roles of LPG during the intracellular stage of Leishmania infection.
- Understanding LPG structure is critical for developing targeted anti-Leishmania therapies.