Novel neogala-series glycosphingolipids with terminal mannose and glucose residues from Hirsutella rhossiliensis, an aureobasidin A-resistant ascomycete fungus

Hirsutella rhossiliensis, a nematophagous fungus belonging to the Ascomycota, is resistant to aureobasidin A (AbA). In this fungus, the biosynthetic pathway leading to mannosylinositolphosphoceramides, which is inhibited by AbA, was not detected. Instead, this fungus contains neutral complex glycosphingolipids (GSLs) and monoglycosylceramides. Except for monoglycosylceramides, neutral GSLs share a neogala-series core structure, Gal beta 1-6Gal beta 1-Cer. Among the GSLs of H. rhossiliensis, three novel GSLs with terminal Man and Glc residues on the sugar chain were elucidated. We analyzed GSL structure using compositional sugar, fatty acid, and sphingoid analyses, methylation analysis, matrix-assisted laser desorption ionization time-of-flight/mass spectrometry (MALDI-TOF MS), and (1)H nuclear magnetic resonance spectroscopy (NMR). The following structures were determined: Man alpha 1-3Gal beta 1-6Gal beta 1-6Gal beta 1-Cer; Glc alpha 1-2Gal beta 1-6Gal beta 1-6Gal beta 1-Cer; and Man alpha 1-3Gal beta 1-6(Glc alpha 1-4)Gal beta 1-6Gal beta 1-Cer. In the ceramides, the fatty acids were predominantly saturated h24:0-acids and the sphingoids were predominately t18:0- or t18:1-sphingoids. In contrast, the ceramides of Glc beta 1-Cer contained d18:2- and d19:2-sphingoids. These findings indicate the presence of a novel biosynthetic pathway of neogala-series GSLs in fungi.