Molecular species of cerebrosides in fruiting bodies of Lentinus edodes and their biological activity

Direct LC–ESI–MS/MS analysis of plant glucosylceramide and ceramide species with 8E and 8Z isomers of the long chain base

Glucosylceramides and ceramides with 8E and 8Z isomers of the long chain base are found in plants. These isomers have been difficult to quantify separately using liquid chromatography–tandem mass spectrometry (LC–MS/MS) because the isomers have the same retention time, their precursor and product ions have the same m/z values, and plant ceramide standards are not commercially available. Here we tested trial separations using various ODS columns and prepared plant ceramide standards generated by human glucocerebrosidase (imiglucerase) using commercially available plant glucosylceramide standards as the substrates. Consequently, we were able to quantify the isomers based on differences in retention times in a TSKgel ODS-120A column (Tosoh, Tokyo Japan) using LC–electrospray ionization–MS/MS (LC–ESI–MS/MS).

Cerebrosides and Steroids from the Edible Mushroom Meripilus giganteus with Antioxidant Potential

The detailed chemical analysis of the methanol extract of Meripilus giganteus (Pers.) P. Karst. led to the isolation of two new cerebrosides, mericeramides A (1) and B (2) together with cerebroside B (3), ergosterol (4), 3β-hydroxyergosta-7,22-diene (5), cerevisterol (6), 3β-hydroxyergosta-6,8(14),22-triene (7), 3β-O-glucopyranosyl-5,8-epidioxyergosta-6,22-diene (8) and (11E,13E)-9,10-dihydroxy-11,13-octadecadienoic acid (9). The structures of the compounds were determined on the basis of NMR and MS spectroscopic analysis. Mericeramide A (1) is the first representative of halogenated natural cerebrosides. The isolated fungal metabolites 1-9 were evaluated for their antioxidant activity using the oxygen radical absorbance capacity (ORAC) assay. Compounds 2, 5 and 9 proved to possess considerable antioxidant effects, with 2.50 ± 0.29, 4.94 ± 0.37 and 4.27 ± 0.05 mmol TE/g values, respectively. The result obtained gives a notable addition to the chemical and bioactivity profile of M. giganteus, highlighting the possible contribution of this species to a versatile and balanced diet.

Blue light exposure and nutrient conditions influence the expression of genes involved in simultaneous hyphal knot formation in Coprinopsis cinerea

Light and nutrients are crucial environmental factors influencing fungal sexual reproduction. Blue light induces simultaneous hyphal knot formation in Coprinopsis cinerea mycelia grown on low-glucose media but not in mycelia grown on high-glucose media. Many hyphal knots are visible in the arc near the edge of the colony one day after 15 min of blue light stimulation. These findings collectively suggest that blue light accelerates hyphal knot induction in nutrient-limited conditions. Transcriptome analysis revealed that gene expression after light exposure is divided into at least two major stages. In the first stage, genes coding for fasciclin (fas1), cyclopropane-fatty-acyl-phospholipid synthases (cfs1 and cfs2), and putative lipid exporter (nod1) are highly expressed after 1 h of light exposure in the mycelial region where the hyphal knot will be developed. These genes are upregulated by blue light and not influenced by glucose condition and mating. These results suggest that although some of the genes are critical for induction of the hyphal knots, they are not sufficient for hyphal knot development. In the second gene expression stage, genes encoding galectins (cgl1-3), farnesyl cysteine-carboxyl methyltransferases, mating pheromone-containing protein, nucleus protein (ich1), and laccase (lcc1) are specifically upregulated at 10-16 h after blue light exposure when the mycelia are cultivated on low-glucose media. These genes might be involved in the architecture of hyphal knots or signal transduction for further fruiting body development. These results contribute to the understanding of the effect of environmental factors on sexual reproduction in basidiomycetous fungi.

Cerebrosides, extracellular glycolipids secreted by the selective lignin-degrading fungus Ceriporiopsis subvermispora

Ceriporiopsis subvermispora is a selective white-rot fungus that degrades lignin at a site far from the hyphae and extracellular enzymes, without intensive damage to the cellulose. In selective ligninolysis, low molecular mass metabolites play a principal role and amphipathic substances are involved to control the degradation and transport of hydrophobic aromatic molecules, including lignin and lipids; however, secretion of the amphipathic substances by this fungus has not been well understood, except for alk(en)yl itaconates called ceriporic acids, which have a weak amphiphilicity. Herein, we report for the first time that the fungus secretes cerebrosides that are classified as glycosphingolipids. By using liquid chromatography electron spray ionization mass spectrometry (LC-ESI-MS) and nuclear magnetic resonance (NMR) spectroscopy coupled with stable isotope feeding experiments with ¹³C-glucose and ¹⁵N-ammonium sulfate, the cerebrosides were determined to be N-hydroxyoctadecanoyl-1-O-β-d-glucopyranosyl-4E,8E-sphingadienine, N-hydroxyoctadecanoyl-1-O-β-d-glucopyranosyl-4E,8Z-sphingadienine, and N-hydroxyoctadecanoyl-1-O-β-d-glucopyranosyl-9-methyl-4E,8E-sphingadienine. The cerebrosides are strong amphipathic substances and potential metabolites for regulating difference and symbiosis within the microbial community.

Structural analysis of fungal cerebrosides

Of the ceramide monohexosides (CMHs), gluco- and galactosyl-ceramides are the main neutral glycosphingolipids expressed in fungal cells. Their structural determination is greatly dependent on the use of mass spectrometric techniques, including fast atom bombardment-mass spectrometry, electrospray ionization, and energy collision-induced dissociation mass spectrometry. Nuclear magnetic resonance has also been used successfully. Such a combination of techniques, combined with classical analytical separation, such as high-performance thin layer chromatography and column chromatography, has led to the structural elucidation of a great number of fungal CMHs. The structure of fungal CMH is conserved among fungal species and consists of a glucose or galactose residue attached to a ceramide moiety containing 9-methyl-4,8-sphingadienine with an amidic linkage to hydroxylated fatty acids, most commonly having 16 or 18 carbon atoms and unsaturation between C-3 and C-4. Along with their unique structural characteristics, fungal CMHs have a peculiar subcellular distribution and striking biological properties. Fungal cerebrosides were also characterized as antigenic molecules directly or indirectly involved in cell growth or differentiation in Schizophyllum commune, Cryptococcus neoformans, Pseudallescheria boydii, Candida albicans, Aspergillus nidulans, Aspergillus fumigatus, and Colletotrichum gloeosporioides. Besides classical techniques for cerebroside (CMH) analysis, we now describe new approaches, combining conventional thin layer chromatography and mass spectrometry, as well as emerging technologies for subcellular localization and distribution of glycosphingolipids by secondary ion mass spectrometry and imaging matrix-assisted laser desorption ionization time-of-flight.

Effect of anti-glycosphingolipid monoclonal antibodies in pathogenic fungal growth and differentiation. Characterization of monoclonal antibody MEST-3 directed to Manpalpha1-->3Manpalpha1-->2IPC

Background

Studies carried out during the 1990's demonstrated the presence of fungal glycoinositol phosphorylceramides (GIPCs) with unique structures, some of them showed reactivity with sera of patients with histoplasmosis, paracoccidioidomycosis or aspergillosis. It was also observed that fungal GIPCs were able to inhibit T lymphocyte proliferation "in vitro", and studies regarding the importance of these molecules to fungal survival showed that many species of fungi are vulnerable to inhibitors of sphingolipid biosynthesis.

Results

In this paper, we describe a detailed characterization of an IgG2a monoclonal antibody (mAb), termed MEST-3, directed to the Paracoccidioides brasiliensis glycolipid antigen Pb-2 (Manpα1→3Manpα1→2IPC). mAb MEST-3 also recognizes GIPCs bearing the same structure in other fungi. Studies performed on fungal cultures clearly showed the strong inhibitory activity of MEST-3 on differentiation and colony formation of Paracoccidioides brasiliensis, Histoplasma capsulatum and Sporothrix schenckii. Similar inhibitory results were observed when these fungi where incubated with a different mAb, which recognizes GIPCs bearing terminal residues of β-D-galactofuranose linked to mannose (mAb MEST-1). On the other hand, mAb MEST-2 specifically directed to fungal glucosylceramide (GlcCer) was able to promote only a weak inhibition on fungal differentiation and colony formation.

Conclusions

These results strongly suggest that mAbs directed to specific glycosphingolipids are able to interfere on fungal growth and differentiation. Thus, studies on surface distribution of GIPCs in yeast and mycelium forms of fungi may yield valuable information regarding the relevance of glycosphingolipids in processes of fungal growth, morphological transition and infectivity.

Molecular cloning and characterization of OsCDase, a ceramidase enzyme from rice

SUMMARY

Sphingolipids are a structurally diverse group of molecules based on long-chain sphingoid bases that are found in animal, fungal and plant cells. In contrast to the situation in animals and yeast, much less is known about the spectrum of sphingolipid species in plants and the roles they play in mediating cellular processes. Here, we report the cloning and characterization of a plant ceramidase from rice (Oryza sativa spp. Japonica cv. Nipponbare). Sequence analysis suggests that the rice ceramidase (OsCDase) is similar to mammalian neutral ceramidases. We demonstrate that OsCDase is a bona fide ceramidase by heterologous expression in the yeast double knockout mutant Deltaypc1Deltaydc1 that lacks the yeast ceramidases YPC1p and YDC1p. Biochemical characterization of OsCDase showed that it exhibited classical Michaelis-Menten kinetics, with optimum activity between pH 5.7 and 6.0. OsCDase activity was enhanced in the presence of Ca(2+), Mg(2+), Mn(2+) and Zn(2+), but inhibited in the presence of Fe(2+). OsCDase appears to use ceramide instead of phytoceramide as a substrate. Subcellular localization showed that OsCDase is localized to the endoplasmic reticulum and Golgi, suggesting that these organelles are sites of ceramide metabolism in plants.

An essential gene for fruiting body initiation in the basidiomycete Coprinopsis cinerea is homologous to bacterial cyclopropane fatty acid synthase genes

The self-compatible Coprinopsis cinerea homokaryon AmutBmut produces fruiting bodies without prior mating to another strain. Early stages of fruiting body development include the dark-dependent formation of primary hyphal knots and their light-induced transition to the more compact secondary hyphal knots. The AmutBmut UV mutant 6-031 forms primary hyphal knots, but development arrests at the transition state by a recessive defect in the cfs1 gene, isolated from a cosmid library by mutant complementation. A normal primordia phenotype was achieved when cfs1+ was embedded at both sides in at least 4.0 kb of native flanking DNA. Truncations of the flanking DNA lead to reduction in transformation frequencies and faults in primordia tissue formation, suggesting that the gene is also acting at later stages of development. The cfs1 gene encodes a protein highly similar to cyclopropane fatty acid synthases, a class of enzymes shown in prokaryotes and recently in a plant to convert membrane-bound unsaturated fatty acids into cyclopropane fatty acids. In C. cinerea 6-031, the mutant cfs1 allele carries a T-to-G transversion, leading to an amino acid substitution (Y441D) in a domain suggested to be involved in the catalytic function of the protein and/or membrane interaction.

Glycosphingolipid structural analysis and glycosphingolipidomics

Sphingosines, or sphingoids, are a family of naturally occurring long-chain hydrocarbon derivatives sharing a common 1,3-dihydroxy-2-amino-backbone motif. The majority of sphingolipids, as their derivatives are collectively known, can be found in cell membranes in the form of amphiphilic conjugates, each composed of a polar head group attached to an N-acylated sphingoid, or ceramide. Glycosphingolipids (GSLs), which are the glycosides of either ceramide or myo-inositol-(1-O)-phosphoryl-(O-1)-ceramide, are a structurally and functionally diverse sphingolipid subclass; GSLs are ubiquitously distributed among all eukaryotic species and are found in some bacteria. Since GSLs are secondary metabolites, direct and comprehensive analysis (metabolomics) must be considered an essential complement to genomic and proteomic approaches for establishing the structural repertoire within an organism and deducing its possible functional roles. The glycosphingolipidome clearly comprises an important and extensive subset of both the glycome and the lipidome, but the complexities of GSL structure, biosynthesis, and function form the outlines of a considerable analytical problem, especially since their structural diversity confers by extension an enormous variability with respect to physicochemical properties. This chapter covers selected developments and applications of techniques in mass spectrometric (MS) that have contributed to GSL structural analysis and glycosphingolipidomics since 1990. Sections are included on basic characteristics of ionization and fragmentation of permethylated GSLs and of lithium-adducted nonderivatized GSLs under positive-ion electrospray ionization mass spectrometry (ESI-MS) and collision-induced mass spectrometry (CID-MS) conditions; on the analysis of sulfatides, mainly using negative-ion techniques; and on selected applications of ESI-MS and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to emerging GSL structural, functional, and analytical issues. The latter section includes a particular focus on evolving techniques for analysis of gangliosides, GSLs containing sialic acid, as well as on characterizations of GSLs from selected nonmammalian eukaryotes, such as dipterans, nematodes, cestodes, and fungi. Additional sections focus on the issue of whether it is better to leave GSLs intact or remove the ceramide; on development and uses of thin-layer chromatography (TLC) blotting and TLC-MS techniques; and on emerging issues of high-throughput analysis, including the use of flow injection, liquid chromatography mass spectrometry (LC-MS), and capillary electrophoresis mass spectrometry (CE-MS).

Membrane lipid profile of an edible basidiomycete Lentinula edodes during growth and cell differentiation

The basidiomycetous mushroom Lentinula edodes (Shiitake) exhibits a unique process of cell differentiation termed "fruiting-body formation". To clarify the relationship between membrane lipids and fruiting-body formation in this fungus, we investigated variations in levels of phospholipids, cerebrosides, fatty acyl residues in the major phospholipids, and fatty acyl and sphingoid base residues in cerebrosides during vegetative growth and fruiting-body formation. PC, PE, and PS were the primary phospholipids in the cells of L. edodes. After a shift in growth temperature of L. edodes mycelia has been shifted from 25 to 18 degrees C, the proportion of unsaturated FA (UFA), such as linoleic acid (18:2) and oleic acid (18:1), increased. In contrast, during fruiting-body formation induced by the temperature downshift to 18 degrees C, 18:2 of PC in the primordia and fruiting bodies decreased, and the UFA of PE and 18:1 of PC increased compared with the proportions in mycelia growing at 18 degrees C. These results showed that the proportions of fatty acyl residues in PC and PE differed during fruiting-body formation in L. edodes. Moreover, the amount of cerebrosides in primordia increased compared with those in mycelia and fruiting bodies and, in these differentiating tissues, the proportion of 2-hydroxypentadecanoic acid increased whereas that of 2-hydroxyoctadecanoic acid decreased compared with that in the mycelia. However, the proportion of sphingoid base residues in cerebrosides did not change during fruiting-body formation in L. edodes.

Antibacterial and xanthine oxidase inhibitory cerebrosides from Fusarium sp. IFB-121, and endophytic fungus in Quercus variabilis

Two antibacterial and xanthine oxidase inhibitory cerebrosides, one of which is chemically new, were characterized from the chloroform-methanol (1:1) extract of Fusarium sp. IFB-121, an endophytic fungus in Quercus variabilis. By means of chemical and spectral methods [IR, electrospray ionization MS (ESI-MS), tandem ESI-MS, 1H and 13C NMR, distortionless enhancement by polarization transfer, COSY, heteronuclear multiple-quantum coherence, heteronuclear multiple-bond correlation, and 2-D nuclear Overhauser effect correlation spectroscopy], the structure of the new metabolite named fusaruside was established as (2S,2'R,3R,3'E,4E,8E,10E)-1-O-beta-D-glucopyranosyl-2-N-(2'-hydroxy-3'-octadecenoyl)-3-hydroxy-9-methyl-4,8,10-sphingatrienine, and the structure of the other was identified as (2S,2'R,3R,3'E,4E,8E)-1-O-beta-D-glucopyranosyl-2-N-(2'-hydroxy-3'-octadecenoyl)-3-hydroxy-9-methyl-4,8-sphingadienine. Both new and known cerebrosides, although inactive to Trichophyton rubrum and Candida albicans, showed strong antibacterial activities against Bacillus subtilis, Escherichia coli, and Pseudomonas fluorescens, with their minimum inhibitory concentrations being 3.9, 3.9, and 1.9 microg/mL, and 7.8, 3.9, and 7.8 microg/mL, respectively. Furthermore, both metabolites were inhibitory to xanthine oxidase, with the IC50 value of fusaruside being 43.8 +/- 3.6 microM and the known cerebroside being 55.5 +/- 1.8 microM.

Structure and biological functions of fungal cerebrosides

Ceramide monohexosides (CMHs, cerebrosides) are glycosphingolipids composed of a hydrophobic ceramide linked to one sugar unit. In fungal cells, CMHs are very conserved molecules consisting of a ceramide moiety containing 9-methyl-4,8-sphingadienine in amidic linkage to 2-hydroxyoctadecanoic or 2-hydroxyhexadecanoic acids, and a carbohydrate portion consisting of one residue of glucose or galactose. 9-Methyl 4,8-sphingadienine-containing ceramides are usually glycosylated to form fungal cerebrosides, but the recent description of a ceramide dihexoside (CDH) presenting phytosphingosine in Magnaporthe grisea suggests the existence of alternative pathways of ceramide glycosylation in fungal cells. Along with their unique structural characteristics, fungal CMHs have a peculiar subcellular distribution and striking biological properties. In Pseudallescheria boydii, Candida albicans, Cryptococcus neoformans, Aspergillus nidulans, A. fumigatus, and Schizophyllum commune, CMHs are apparently involved in morphological transitions and fungal growth. The elucidation of structural and functional aspects of fungal cerebrosides may therefore contribute to the design of new antifungal agents inhibiting growth and differentiation of pathogenic species.

Plant sphingolipids: structural diversity, biosynthesis, first genes and functions

In mammals and Saccharomyces cerevisiae, sphingolipids have been a subject of intensive research triggered by the interest in their structural diversity and in mammalian pathophysiology as well as in the availability of yeast mutants and suppressor strains. More recently, sphingolipids have attracted additional interest, because they are emerging as an important class of messenger molecules linked to many different cellular functions. In plants, sphingolipids show structural features differing from those found in animals and fungi, and much less is known about their biosynthesis and function. This review focuses on the sphingolipid modifications found in plants and on recent advances in the functional characterization of genes gaining new insight into plant sphingolipid biosynthesis. Recent studies indicate that plant sphingolipids may be also involved in signal transduction, membrane stability, host-pathogen interactions and stress responses.

Glucosylceramide synthases, a gene family responsible for the biosynthesis of glucosphingolipids in animals, plants, and fungi

Glucosylceramides are membrane lipids in most eukaryotic organisms and in a few bacteria. The physiological functions of these glycolipids have only been documented in mammalian cells, whereas very little information is available of their roles in plants, fungi, and bacteria. In an attempt to establish appropriate experimental systems to study glucosylceramide functions in these organisms, we performed a systematic functional analysis of a glycosyltransferase gene family with members of animal, plant, fungal, and bacterial origin. Deletion of such putative glycosyltransferase genes in Candida albicans and Pichia pastoris resulted in the complete loss of glucosylceramides. When the corresponding knock-out strains were used as host cells for homologous or heterologous expression of candidate glycosyltransferase genes, five novel glucosylceramide synthase (UDP-glucose:ceramide glucosyltransferase) genes were identified from the plant Gossypium arboreum (cotton), the nematode Caenorhabditis elegans, and the fungi Magnaporthe grisea, Candida albicans, and P. pastoris. The glycosyltransferase gene expressions led to the biosynthesis of different molecular species of glucosylceramides that contained either C18 or very long chain fatty acids. The latter are usually channeled exclusively into inositol-containing sphingolipids known from Saccharomyces cerevisiae and other yeasts. Implications for the biosynthesis, transport, and function of sphingolipids will be discussed.

Sterol glycosides and cerebrosides accumulate in Pichia pastoris, Rhynchosporium secalis and other fungi under normal conditions or under heat shock and ethanol stress

The occurrence of glycolipids such as sterol glycosides, acylated sterol glycosides, cerebrosides and glycosyldiacylglycerols was examined in the three yeast species Candida albicans, Pichia pastoris and Pichia anomala, as well as in the six fungal species Sordaria macrospora, Pyrenophora teres, Ustilago maydis, Acremonium chrysogenum, Penicillium olsonii and Rhynchosporium secalis. Cerebroside was found in all organisms tested, whereas acylated sterol glycosides and glycosyldiacylglycerols were not found in any organism. Sterol glycosides were detected in P. pastoris strain GS115, U. maydis, S. macrospora and R. secalis. This glycolipid occurred in both yeast and filamentous forms of U. maydis but in neither form of C. albicans. This suggests that sterol glycoside is not correlated with the separately grown dimorphic forms of these organisms. Cerebrosides and sterol glycosides from P. pastoris and R. secalis were purified and characterized by mass spectrometry and nuclear magnetic resonance spectroscopy. The cerebrosides are beta-glucosyl ceramides consisting of a saturated alpha-hydroxy or non-hydroxy fatty acid and a Delta4,8-diunsaturated, C9-methyl-branched sphingobase. Sterol glycoside from P. pastoris was identified as ergosterol-beta-D-glucopyranoside, whereas the sterol glucosides from R. secalis contain two derivatives of ergosterol. The biosynthesis of sterol glucoside in P. pastoris CBS7435 and GS115 depended on the culture conditions. The amount of sterol glucoside in cells grown in complete medium was much lower than in cells from minimal medium and a strong increase in the content of sterol glucoside was observed when cells were subjected to stress conditions such as heat shock or increased ethanol concentrations. From these data we suggest that, in addition to Saccharomyces cerevisiae, new yeast and fungal model organisms should be used to study the physiological functions of glycolipids in eukaryotic cells. This suggestion is based on the ubiquitous and frequent occurrence of cerebrosides and sterol glycosides, both of which are rarely detected in S. cerevisiae. We suggest P. pastoris and two plant pathogenic fungi to be selected for this approach.

Characterization of monoclonal antibody MEST-2 specific to glucosylceramide of fungi and plants

An IgG2a monoclonal antibody anti-glucosylceramide was established and termed MEST-2. High performance thin layer chromatography immunostaining, and solid-phase radioimmunoassay showed that MEST-2 reacts with glucosylceramide from yeast and mycelium forms of Paracoccidioides brasiliensis, Histoplasma capsulatum, and Sporothrix schenckii; from hyphae of Aspergillus fumigatus; and from yeast forms of Candida albicans, Cryptococcus neoformans, Cryptococcus laurentii, and Cryptococcus albidus. Studies on the fine specificity of MEST-2 showed that it recognizes the beta-D-glucose residue, and that the 2-hydroxy group present in the fatty acid is an important auxiliary feature for the antibody binding. It was also demonstrated that phosphatidylcholine and ergosterol modulate MEST-2 reactivity to glucosylceramide, by solid-phase radioimmunoassay. Indirect immunofluorescence showed that MEST-2 reacts with the surface of yeast forms of P. brasiliensis, H. capsulatum and S. schenckii. Weak staining of mycelial forms of P. brasiliensis and hyphae of A. fumigatus was also observed. The availability of a monoclonal antibody specific to fungal glucosylceramide, and its potential use in analyzing biological roles attributed to glucosylceramide in fungi are discussed.

Characterization of cerebrosides from the thermally dimorphic mycopathogen Histoplasma capsulatum: expression of 2-hydroxy fatty N-acyl (E)-Delta(3)-unsaturation correlates with the yeast-mycelium phase transition

Cerebroside (monohexosylceramide) components were identified in neutral lipids extracted from both the yeast and mycelial forms of the thermally dimorphic mycopathogen Histoplasma capsulatum. The components were purified from both forms and their structures elucidated by 1- and 2-dimensional nuclear magnetic resonance (NMR) spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and low energy tandem collision-induced dissociation mass spectrometry (ESI-MS/CID-MS). Both components were characterized as beta-glucopyranosylceramides (GlcCers) containing (4E,8E)-9-methyl-4,8-sphingadienine as the long-chain base, attached to 18-carbon 2-hydroxy fatty N-acyl components. However, while the fatty acid of the yeast form GlcCer was virtually all N-2'-hydroxyoctadecanoate, the mycelium form GlcCer was characterized by almost exclusive expression of N-2'-hydroxy-(E)-delta(3)-octadecenoate. These results suggest that the yeast-mycelium transition is accompanied by up-regulation of an as yet uncharacterized ceramide or cerebroside 2-hydroxy fatty N-acyl (E)-delta(3)-desaturase activity. They also constitute further evidence for the existence of two distinct pathways for ceramide biosynthesis in fungi, since glycosylinositol phosphorylceramides (GIPCs), the other major class of fungal glycosphingolipids, are found with ceramides consisting of 4-hydroxysphinganine (phytosphingosine) and longer chain 2-hydroxy fatty acids. In addition to identification of the major glucocerebroside components, minor components (< 5%) detectable by molecular weight differences in the ESI-MS profiles were also characterized by tandem ESI-MS/CID-MS analysis. These minor components were identified as variants differing in fatty acyl chain length, or the absence of the sphingoid 9-methyl group or (E)-delta(8)-unsaturation, and are hypothesized to be either biosynthetic intermediates or the result of imperfect chemical transformation by the enzymes responsible for these features. Possible implications of these findings with respect to chemotaxonomy, compartmentalization of fungal glycosphingolipid biosynthetic pathways, and regulation of morphological transitions in H.capsulatum and other dimorphic fungi are discussed.

General and efficient syntheses of C(18)-4,8-sphingadienines via S(N)2'-type homoallylic coupling reactions mediated by thioether-stabilized copper reagents

The stereoselective syntheses of C(18)-4,8-sphingadienines 3 and 4 as analogues of sphingosine 1 are described. The key step in these syntheses involved a novel S(N)2'-type homoallylic coupling reaction between the corresponding thioether-stabilized allylic copper reagents and the allylic mesylate 7. The thioether-stabilized allylic copper reagents were easily prepared and retained the configuration of their double bond during the coupling reactions, thus overcoming the problem of isomerization which was normally associated with the use of allylic organometallic reagents in such applications.

Yeast sphingolipids

Many advances in our understanding of fungal sphingolipids have been made in recent years. This review focuses on the types of sphingolipids that have been found in fungi and upon the genes in Saccharomyces cerevisiae, the common baker's yeast, that are necessary for sphingolipid metabolism. While only a small number of fungi have been examined, most contain sphingolipids composed of ceramide derivatized at carbon-1 with inositol phosphate. Further additions include mannose and then other carbohydrates. The second major class of fungal sphingolipids is the glycosylceramides, having either glucose or galactose attached to ceramide rather than inositol phosphate. The glycosylceramides sometimes contain additional carbohydrates. Knowledge of the genome sequence has expedited identification of S. cerevisiae genes necessary for sphingolipid metabolism. At least one gene is known for most steps in S. cerevisiae sphingolipid metabolism, but more are likely to be identified so that the 13 known genes are likely to grow in number. The AUR1 gene is necessary for addition of inositol phosphate to ceramide and has been identified as a target of several potent antifungal compounds. This essential step in yeast sphingolipid synthesis, which is not found in humans, appears to be an excellent target for the development of more effective antifungal compounds, both for human and for agricultural use.

Cerebrosides A and C, sphingolipid elicitors of hypersensitive cell death and phytoalexin accumulation in rice plants

When plants interact with certain pathogens, they protect themselves by generating various chemical and physical barriers called the hypersensitive response. These barriers are induced by molecules called elicitors that are produced by pathogens. In the present study, the most active elicitors of the hypersensitive response in rice were isolated from the rice pathogenic fungus Magnaporthe grisea, and their structures were identified as cerebrosides A and C, sphingolipids that were previously isolated as inducers of cell differentiation in the fungus Schizophyllum commune. Treatment of rice leaves with cerebroside A induced the accumulation of antimicrobial compounds (phytoalexins), cell death, and increased resistance to subsequent infection by compatible pathogens. The degradation products of cerebroside A (fatty acid methyl ester, sphingoid base, and glucosyl sphingoid base) showed no elicitor activity. Hydrogenation of the 8E-double bond in the sphingoid base moiety or the 3E-double bond in the fatty acid moiety of cerebroside A did not alter the elicitor activity, whereas hydrogenation of the 4E-double bond in the sphingoid base moiety led to a 12-fold decrease in elicitor activity. Furthermore, glucocerebrosides from Gaucher's spleen consisting of (E)-4-sphingenine and cerebrosides from rice bran mainly consisting of (4E,8E)-4,8-sphingadienine and (4E,8Z)-4,8-sphingadienine showed no elicitor activity. These results indicate that the methyl group at C-9 and the 4E-double bond in the sphingoid base moiety of cerebrosides A and C are the key elements determining the elicitor activity of these compounds. This study is the first to show that sphingolipids have elicitor activity in plants.

Identification of ceramide-phosphorylethanolamine in oomycete plant pathogens: Pythium ultimum, Phytophthora infestans, and Phytophthora capsici

Cellular lipids were extracted from three species of Oomycete plant pathogens (Pythium ultimum, Phytophthora infestans, and Ph. capsici) and analyzed via normal-phase high-performance liquid chromatography with flame-ionization detection. The most abundant polar lipids in each of the three species were the polar membrane lipids, phosphatidylethanolamine (PE), phosphatidylcholine, and a phosphosphingolipid that eluted soon after PE. Structural analysis via mass spectrometry and nuclear magnetic resonance spectrometry revealed that the phosphosphingolipid was ceramide phosphorylethanolamine (Cer-PE). The most abundant molecular species of Cer-PE in P. ultimum had a molecular weight of 670.5, contained an unusual 19-carbon branched triunsaturated sphingoid (C19-delta 4, 8, 10, 9-methyl long-chain base) and palmitic acid as the amide-linked fatty acid. The most abundant molecular species of Cer-PE in Ph. infestans had a molecular weight of 714.5, contained a common 16-carbon 1,3 di-OH sphingoid, and erucic (cis 13-docosenoic, C22-delta 13) acid as the amide-linked fatty acid. The Cer-PE in Ph. capsici comprised a mixture of each of the two molecular species found in P. ultimum and Ph. infestans.

The glycosylceramides of the nematode Caenorhabditis elegans contain an unusual, branched-chain sphingoid base

Caenorhabditis elegans was cultured in semi-defined medium containing yeast extract, soy peptone, glucose, hemoglobin, Tween 80, and sitosterol. Monoglycosylceramides were chromatographically purified from nematode extracts. Their structures were elucidated with mass spectrometry, nuclear magnetic resonance spectroscopy, and analysis of methanolysis products of the parent cerebrosides. The glycosylceramides were unusual in that the only long-chain sphingoid base detected was an iso-branched compound with a C-4 double bond (i.e., 15-methyl-2-aminohexadec-4-en-1,3-diol). Glucose was the only sugar moiety detected. The fatty acids consisted of a series of primarily straight-chain, saturated, 2-hydroxylated C20-C26 acids; some iso-branched analogs also occurred. The sphingomyelins of C. elegans were also hydrolyzed, and the same iso-branched C17 compound was the only sphingoid base detected. This is the first structural analysis of a nematode glycosphingolipid and the first report of an organism in which the long-chain sphingoid bases are entirely iso-branched.