Identification of the galactosyltransferase of Cryptococcus neoformans involved in the biosynthesis of basidiomycete-type glycosylinositolphosphoceramide

Therese Wohlschlager, Reto Buser, Michael L. Skowyra, Brian C. Haynes, Bernard Henrissat, Tamara L. Doering, Markus Künzler, Markus Aebi

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

The pathogenic fungus Cryptococcus neoformans synthesizes a complex family of glycosylinositolphosphoceramide (GIPC) structures. These glycosphingolipids (GSLs) consist of mannosylinositolphosphoceramide (MIPC) extended by β1-6-linked galactose, a unique structure that has to date only been identified in basidiomycetes. Further extension by up to five mannose residues and a branching xylose has been described. In this study, we identified and determined the gene structure of the enzyme Ggt1, which catalyzes the transfer of a galactose residue to MIPC. Deletion of the gene in C. neoformans resulted in complete loss of GIPCs containing galactose, a phenotype that could be restored by the episomal expression of Ggt1 in the deletion mutant. The entire annotated open reading frame, encoding a C-terminal GT31 galactosyltransferase domain and a large N-terminal domain of unknown function, was required for complementation. Notably, this gene does not encode a predicted signal sequence or transmembrane domain. The demonstration that Ggt1 is responsible for the transfer of a galactose residue to a GSL thus raises questions regarding the topology of this biosynthetic pathway and the function of the N-terminal domain. Phylogenetic analysis of the GGT1 gene shows conservation in hetero- and homobasidiomycetes but no homologs in ascomycetes or outside of the fungal kingdom.

Original languageEnglish
Pages (from-to)1210-1219
Number of pages10
JournalGlycobiology
Volume23
Issue number11
DOIs
StatePublished - Nov 2013

Keywords

  • Basidiomycete
  • Fungal glycans
  • Galactosyltransferase
  • Gipc
  • Glycolipids

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