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Structure and antigenicity of the lipophosphoglycan from Leishmania major amastigotes
S F Moody1, E Handman, A Bacic
1Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Victoria, Australia.
Abstract:
The lipophosphoglycan (LPG) of the intracellular amastigote form of the protozoan parasite Leishmania major is chemically distinct from the LPG on the surface of the extracellular promastigote form. Amastigote LPG is composed of the monosaccharides galactose, glucose, mannose, glucosamine and inositol in the molar ratio 51:30:24:1:1; arabinose is absent. The lipid anchor comprises four alkylglycerols, with alkyl chain lengths 24:0, 22:0, 20:0 and 26:0 in the molar ratio 68:18:8:6. Phosphate is present at 4% w/w of total carbohydrate. HPLC gel permeation reveals LPG to be a polydisperse family of molecules Mr 100-6 kDa. The results from immunological studies with LPG-directed antibodies are consistent with amastigote LPG having the expected tripartite structure of GPI-anchor, a core glycan and the phosphorylated disaccharide repeat backbone. Human sera from L. major patients bound amastigote LPG in enzyme-linked immunosorbent assays.
Insights
The lipophosphoglycan (LPG) from Leishmania major amastigotes differs chemically from promastigote LPG. This study characterizes amastigote LPG structure and its interaction with patient sera.
Area of Science:
- Parasitology
- Glycobiology
- Immunochemistry
Background:
- Lipophosphoglycan (LPG) is a major surface glycoconjugate of Leishmania parasites.
- LPG structure and function vary between developmental stages (promastigote and amastigote).
- Understanding amastigote LPG is crucial for developing diagnostics and therapeutics for leishmaniasis.
Purpose of the Study:
- To chemically characterize the lipophosphoglycan (LPG) of the intracellular amastigote form of Leishmania major.
- To compare amastigote LPG with the promastigote form.
- To investigate the potential of amastigote LPG as a diagnostic marker.
Main Methods:
- Monosaccharide composition analysis using molar ratios.
- Lipid anchor analysis of alkylglycerols and chain lengths.
- High-Performance Liquid Chromatography (HPLC) gel permeation for molecular weight determination.
- Immunological studies using LPG-directed antibodies and human sera.
Main Results:
- Amastigote LPG lacks arabinose and contains galactose, glucose, mannose, glucosamine, and inositol.
- The lipid anchor consists of four alkylglycerols with specific chain lengths and ratios.
- HPLC revealed LPG as a polydisperse family of molecules (100-6 kDa).
- Immunological data support a tripartite structure (GPI-anchor, core glycan, repeat backbone).
- Human sera from Leishmania major patients showed binding to amastigote LPG.
Conclusions:
- Amastigote LPG from Leishmania major possesses a distinct chemical composition and structure compared to promastigote LPG.
- The characterized structure is consistent with a glycosylphosphatidylinositol (GPI) anchor, core glycan, and phosphorylated disaccharide repeats.
- Amastigote LPG shows potential for use in diagnosing Leishmania major infections.