Glycobiology Advance Access originally published online on March 29, 2007
Glycobiology 2007 17(7):754-766; doi:10.1093/glycob/cwm035
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Characterization of neutral and acidic glycosphingolipids from the lectin-producing mushroom, Polyporus squamosus
2 Department of Chemistry, University of New Hampshire, Durham, NH 03824-3598
3 Department of Biochemistry and Molecular Biology, The Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602-7229
4 Department of Biological Chemistry, School of Medicine, University of Michigan, Ann Arbor, MI 48109-0606
1 To whom correspondence should be addressed; Tel: +1-603-862-2529; Fax: +1-603-862-4278; E-mail: slevery{at}cisunix.unh.edu
Received on December 30, 2006; revised on March 15, 2007; accepted on March 18, 2007
The polypore mushroom Polyporus squamosus is the source of a lectin that exhibits a general affinity for terminal ß-galactosides, but appears to have an extended carbohydrate-binding site with high affinity and strict specificity for the nonreducing terminal trisaccharide sequence NeuAc
2 
6Galß1 4Glc/GlcNAc. In considering the possibility that the lectin's in vivo function could involve interaction with an endogenous glycoconjugate, it would clearly be helpful to identify candidate ligands among various classes of carbohydrate-containing materials expressed by P. squamosus. Since evidence has been accumulating that glycosphingolipids (GSLs) may serve as key ligands for some endogenous lectins in animal species, possible similar roles for fungal GSLs could be considered. For this study, total lipids were extracted from mature fruiting body of P. squamosus. Multistep fractionation yielded a major monohexosylceramide (CMH) component and three major glycosylinositol phosphorylceramides (GIPCs) from the neutral and acidic lipids, respectively. These were characterized by a variety of techniques as required, including one- and two-dimensional 1H- and 13C-nuclear magnetic resonance (NMR) spectroscopy; electrospray ionization–mass spectrometry (ESI-MS, tandem-MS/collision-induced decay-MS, and ion trap-MSn); and component and methylation linkage analysis by gas chromatography–mass spectrometry. The CMH was determined to be glucosylceramide having a typical ceramide consisting of 2-hydroxy fatty-N-acylated (4E,8E)-9-methyl-sphinga-4,8-dienine. The GIPCs were identified as Man1 2Ins1-P-1Cer (Ps-1), Galß1 6Man1 2Ins1-P-1Cer (Ps-2), and Man1 3Fuc1 2Gal1 6Galß1 6Man1 2Ins1-P-1Cer (Ps-5), respectively (where Ins = myo-inositol, P = phosphodiester, and Cer = ceramide consisting mainly of long-chain 2-hydroxy and 2,3-dihydroxy fatty-N-acylated 4-hydroxy-sphinganines). Of these GSLs, Ps-2 could potentially interact with P. squamosus lectin, and further investigations will focus on determining the binding affinity, if any, of the lectin for the GIPCs isolated from this fungus.
Key words: basidiomycete / electrospray ionization / glycolipid / mass spectrometry / NMR spectroscopy
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