The structure of a complex glycosylphosphatidyl inositol-anchored glucoxylan from the kinetoplastid protozoan Leptomonas samueli

The structure of a glycosylphosphatidyl inositol-anchored glucoxylan (GPI-g lucoxylan) synthesized by the monogenetic trypanosomatid Leptomonas samueli has been determined. The glucoxylan is anchored to the membrane by phytoce ramide and an oligosaccharide core, the structure of which is identical to glycoinositolphospholipids (GIPLs) expressed by this protozoan. The glucoxy lan chain is linear, containing --> 4Glc alpha 1 -->, --> 4Xyl beta 1 --> a nd --> 3Xyl beta 1 --> residues. A well defined sequence heterogeneity was analysed in terms of a series of overlapping trisaccharide substructures. A proportion of the chains are capped with a GlcA alpha 1 --> 3Glc alpha 1 - -> sequence. While an average GlcA-capped chain contained 10 Glc and 16 Xyl residues, uncapped chains have a higher molecular mass with an average of 30 Glc and 50 Xyl per chain. We propose a mode of biosynthesis based on the observed structural heterogeneity.