Comparative analysis of ceramide structural modification found in fungal cerebrosides by electrospray tandem mass spectrometry with low energy collision‐induced dissociation of Li adduct ions

Abstract

both yeast and mycelium forms). The major components of all species examined differed primarily (and widely) in the level of 2-hydroxy fatty N-acyl D 3 unsaturation, but among the minor components a significant degree of additional structural diversity was observed, based on differences in sphingoid or N-acyl chain length, as well as on the presence or absence of the sphingoid D 8 unsaturation or 9-methyl group. Some variants were isobaric, and were not uniformly present in all species, affirming the need for MS/CID-MS analysis for full characterization of all components in a fungal CMH fraction. The diversity in ceramide distribution observed may reflect significant species-specific differences among fungi with respect to cerebroside biosynthesis and function.

Neutral glycolipids of the filamentous fungus Neurospora crassa:altered expression in plant defensin-resistant mutants

“…As found previously with MS/CID-MS spectra acquired on a triple quadrupole instrument (25,26), key ions diagnostic for fatty-N-acyl and sphingoid carbon number and level of unsaturation can be observed at high abundance in the hybrid Q-TOF spectra, but with the expected increases in overall sensitivity, resolution, and mass accuracy. In the CID spectrum of the major [MϩLi] ϩ at m/z 760, an O ion, corresponding to loss of the fatty-N-acyl chain (Scheme 2), is observed abundantly at m/z 480, characteristic for a monohexosyl-(4E,8E)-9-methyl-4,8-sphingadienine (25). Additional loss of the hexose moiety yields a confirming N ion, appearing in this spectrum at m/z 318.…”

“…For example, in the CID spectrum of the minor [MϩLi] ϩ at m/z 746 (Fig. 4B), 14 u decrements are observed almost exclusively for the O and N ions (m/z 466 and 304, respectively) but not for the T and W ions, consistent with lack of the branching methyl group on the sphingoid but not with h17:1 fatty-N-acylation [this is not always the case (25,26)]. On the other hand, in the CID spectrum of [MϩLi] ϩ at m/z 732 (Table 1), O and N ions are again observed at m/z 480 and 318, respectively, but the T and W ions are decremented to m/z 302 and 231, respectively, consistent with h16:1 fatty-N-acylation.…”

“…As described previously (25,26), to generate [M ϩ Li] ϩ adducts of GlcCer molecular species, LiI (10 mM) in methanol was added to the analyte solution until the observed ratio of [M ϩ Li] ϩ adducts to mixed Na ϩ /Li ϩ adducts in MS profile mode was Ͼ 5:1; the necessary LiI concentration was generally in the range 2-3 mM. Resolution was generally 4,000 (5% valley) for positive ion mode ESI ( ϩ ESI)-Q-TOF-MS molecular adduct profile spectra and 3,000 for MS/collision-induced dissociation (CID)-TOF-MS experiments.…”

“…Nominal monoisotopic m/z values are used in the labeling and description of ϩ ESI-MS results. Interpretation of spectra derived from [M ϩ Li] ϩ adducts of GlcCer molecular species was essentially as described previously (25)(26)(27).…”

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.…”