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

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.

Genetic alteration of UDP‐rhamnose metabolism in Botrytis cinerea leads to the accumulation of UDP‐KDG that adversely affects development and pathogenicity

“…). Other nucleotide sugars common in most fungi are UDP‐galactopyranose (UDP‐Gal p ) and UDP‐galactofuranose (UDP‐Gal f ), which are used for the synthesis of diverse types of glycoprotein (Lopez‐Fernandez et al ., ) and galactomannans (Tefsen et al ., ); however, UDP‐xylose (Bar‐Peled et al ., ; Klutts et al ., ; Lee et al ., ) and UDP‐glucuronic acid (Bar‐Peled et al ., ; Cherniak et al ., ; Fontaine et al ., ; Wohlschlager et al ., ) are produced only in certain species. In addition to macromolecules, UDP‐sugars are incorporated into secondary metabolites, for instance sterol‐glycosides (Kim et al ., ), and are used for the detoxification of plant defence molecules, such as phytoalexins (Sexton et al ., ).…”

Identification of a putative α-galactoside β-(1 → 3)-galactosyltransferase involved in the biosynthesis of galactomannan side chain of glucuronoxylomannogalactan in Cryptococcus neoformans

“…The putative α-Gal β-(1 → 3)-Gal transferase Pvg3 in Schizosaccharomyces pombe , which belongs to the GT31 family, highlights the diversity of glycosyltransferases ( Andreishcheva et al, 2004 ; Fukunaga et al, 2023 ). In C. neoformans , the genome encodes three GT31 family glycosyltransferases, one of which, Ggt1, functions as an α-Man β-(1 → 6)-Gal transferase in GIPC biosynthesis ( Wohlschlager et al, 2013 ). However, the functions of other presumptive glycosyltransferases of the GT31 family in the C. neoformans genome are unclear.…”