N-linked oligosaccharides obtained from glycoproteins of the lichens Sticta tomentosa and Sticta damaecornis

Abstract

The lichens Sticta tomentosa and Sticta damaecornis were extracted to obtain glycoproteins. The extracts were fractionated with 30-80% saturation (NH4)2SO4. The fractions were reduced, alkylated and after dialysis the material were digested with trypsin. The digests were dialyzed, freeze-dried and analyzed in reverse-phase high performance chromatography (RP-HPLC) based on the peptide hydrophobicity.N-linked oligosaccharides were removed from glycopeptides with PNGase A and analyzed by HPAEC-PAD that indicated the presence of several peaks between 12 to 17 min. The reducing oligosaccharides were reacted with NH4HCO3 to form oligosaccharides-glycosylamines and then derivatized with N-hydroxysuccinimidyl ester of Boc-tyrosine, resulting in tyrosinamide-oligosaccharides with sufficient hydrophobicity to facilitate RP-HPLC separation. RP-HPLC purification of asialyl tyrosinamide oligosaccharides from S. tomentosa showed two peaks eluted at 11 and 18 min. The asialyl tyrosinamide oligosaccharides from S. damaecornis eluted as four peaks at 11, 13, 18,2 and 18,4 min. The components that eluted at 11 min for both lichens showed the same monosaccharide composition.