Glycosylphosphatidylinositol-anchored fungal polysaccharide in Aspergillus fumigatus

Galactomannan is a characteristic polysaccharide of the human filamentous fungal pathogen Aspergillus fumigatus that can be used to diagnose invasive aspergillosis. In this study, we report the isolation of a galactomannan fraction associated to membrane preparations from A. fumigatus mycelium by a lipid anchor. Specific chemical and enzymatic degradations and mass spectrometry analysis showed that the lipid anchor is a glycosylphosphatidylinositol ( GPI). The lipid part is an inositol phosphoceramide containing mainly C-18-phytosphingosine and monohydroxylated lignoceric acid ( 20H-C-24:0 fatty acid). GPI glycan is a tetramannose structure linked to a glucosamine residue: Man alpha 1-2Man alpha 1-2Man alpha 1-6Man alpha 1-4GlcN. The galactomannan polymer is linked to the GPI structure throught the mannan chain. The GPI structure is a type 1, closely related to the one previously described for the GPI-anchored proteins of A. fumigatus. This is the first time that a fungal polysaccharide is shown to be GPI-anchored.