Glycosyl-phosphatidylinositols of Trypanosoma congolense: two common precursors but a new protein-anchor.
The parasitic protozoan Trypanosoma congolense exhibits a dense surface coat which is pivotal for immunoevasion of the parasite. This dense surface coat is made of a single protein species, the variant surface glycoprotein, which is present in a high copy number. The protein is anchored to the plasma membrane by a glycosyl-phosphatidylinositol membrane anchor. A detailed study of the structure of T. congolense strain 423 (clone BENat 1.3) variant surface glycoprotein glycosyl-phosphatidylinositol membrane anchor was performed. Radioactively labelled core-glycan prepared by dephosphorylation, deamination and reduction was analysed by high-pH anion-exchange chromatography, size-exclusion and lectin affinity chromatography. Additionally the glycosyl-phosphatidylinositol membrane anchor core-glycan was purified from a bulk preparation of variant surface glycoprotein and subjected to mass spectrometry and methylation analysis. Using these methods we could identify a novel galactose-beta 1,6-N-acetyl-glucosamine-beta 1,4-branch modifying the mannose adjacent to the glucosamine of the mannose-alpha 1,2-mannose-alpha 1,6-mannose-alpha 1,4-glucosamine core-glycan of the variant surface glycoprotein glycosyl-phosphatidylinositol membrane anchor. Furthermore the biosynthetic pathway leading to this novel structure was investigated. Two putative glycosyl-phosphatidylinositol anchor precursors were identified having structures identical to the previously characterized Trypanosoma brucei brucei glycolipids P2 and P3 (also designated glycolipid A and C) consistent with a trimannosyl core and a dimyristoyl-glycerol. Both glycosyl-phosphatidylinositol anchor precursors of T. congolense do not possess the side-branch modification found on the mature protein membrane anchor, implying that the sugar side-chain is added to the anchor during its passage through the Golgi-apparatus.
Gerold
P
P
Zentrum für Hygiene und Medizinische Mikrobiologie, Philipps-Universität Marburg, Germany.
Striepen
B
B
Reitter
B
B
Geyer
H
H
Geyer
R
R
Reinwald
E
E
Risse
H J
HJ
Schwarz
R T
RT
D000818:Animals; D002240:Carbohydrate Sequence; D017261:Glycosylphosphatidylinositols / Q000096:biosynthesis / Q000737:chemistry*; D006595:Hexosamines / Q000032:analysis; D008358:Mannose / Q000737:chemistry; D008969:Molecular Sequence Data; D011134:Polysaccharides / Q000032:analysis / Q000302:isolation & purification; D014348:Trypanosoma congolense / Q000737:chemistry*; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000096:biosynthesis / Q000737:chemistry*
D017261:Glycosylphosphatidylinositols; D006595:Hexosamines; D011134:Polysaccharides; D014643:Variant Surface Glycoproteins, Trypanosoma; D008358:Mannose