Characterization of glucosylceramides in Pseudallescheria boydii and their involvement in fungal differentiation

Abstract

Pseudallescheria boydii is a fungal pathogen that causes disease in immunocompromised patients. Ceramide monohexosides (CMHs) were purified from lipidic extracts of this fungus, showing that, as described for several other species, P. boydii synthesizes glucosylceramides as major neutral glycosphingolipids. CMHs from P. boydii were analyzed by high-performance thin-layer chromatography, gas chromatography coupled to mass spectrometry, fast atom bombardment-mass spectrometry, and nuclear magnetic resonance. These combination of techniques allowed the identification of CMHs from P. boydii as molecules containing a glucose residue attached to 9-methyl-4,8-sphingadienine in amidic linkage to 2-hydroxyoctadecanoic or 2-hydroxyhexadecanoic acids. Antibodies from a rabbit infected with P. boydii recognized CMHs from this fungus. Antibodies to CMH were purified from serum and used in indirect immunofluorescence, which revealed that CMHs are detectable on the surface of mycelial and pseudohyphal but not conidial forms of P. boydii, suggesting a differential expression of glucosylceramides according with morphological phase. We also investigated the influence of antibodies to CMH on growth and germ tube formation in P. boydii. Cultures that were supplemented with these antibodies failed to form mycelium, but the latter was not affected once formed. Similar experiments were performed to evaluate whether antibodies to CMH would influence germ tube formation in Candida albicans, a fungal pathogen that synthesizes glucosylceramide and uses differentiation as a virulence factor. Addition of antiglucosylceramide antibodies to cultures of C. albicans clearly inhibited the generation of germ tubes. These results indicated that fungal CMHs might be involved in the differentiation and, consequently, play a role on the infectivity of fungal cells.

Defensins from Insects and Plants Interact with Fungal Glucosylceramides

“…Differences in ceramide structure among fungal, plant, and human GlcCer probably account for the observed binding selectivity. GlcCer from various fungal and yeast species, such as P. pastoris (16), C. albicans (19), Lentinus edodes (34), Pseudallescheria boydii (35) and Cryptococcus neoformans (36,37), are identical (Glc-9-methyl-d18:2/h18: (17). Fungal GlcCer show a number of structural features that distinguish them from those found in mammals and plants, such as the 9-methyl group branching of the sphingoid base, variable levels of unsaturation and length of the fatty acid chain.…”

Sphingolipids as Targets for Treatment of Fungal Infections

“…Several natural inhibitors of fungal GlcCer synthesis have been described to exhibit a potent antifungal activity [16][17][18]. In addition, monoclonal antibodies against GlcCer are able to inhibit the growth of different fungi, including C. neoformans, Colletotrichum gloeosporioides, Fonsecaea pedrosoi, Pseudallescheria boydii and Scedosporium apiospermum [19][20][21][22][23].…”

Identification of Fungal Sphingolipid C9-methyltransferases by Phylogenetic Profiling

“…Human patients with a Cryptococcus neoformans infection as well as rabbits infected with Pseudallescheria boydii develop antibodies binding to C9-methylated fungal glucosylceramides. The purified antibodies inhibit fungal growth in culture (17,18). Fungal glucosylceramides can elicit defense responses in rice plants and cell suspension cultures of rice, and treatment with these fungal glucosylceramides protects rice plants against fungal infection (19 -21).…”