Identification of methylated GnTI-dependent N-glycans in Botryococcus brauni

New Phytol. 2017 Sep;215(4):1361-1369. doi: 10.1111/nph.14713. Epub 2017 Jul 24.


In contrast to mammals and vascular plants, microalgae show a high diversity in the N-glycan structures of complex N-glycoproteins. Although homologues for β1,2-N-acetylglucosaminyltransferase I (GnTI), a key enzyme in the formation of complex N-glycans, have been identified in several algal species, GnTI-dependent N-glycans have not been detected so far. We have performed an N-glycoproteomic analysis of the hydrocarbon oils accumulating green microalgae Botryococcus braunii. Thereby, the analysis of intact N-glycopeptides allowed the determination of N-glycan compositions. Furthermore, insights into the role of N-glycosylation in B. braunii were gained from functional annotation of the identified N-glycoproteins. In total, 517 unique N-glycosylated peptides have been identified, including intact N-glycopeptides that harbored N-acetylhexosamine (HexNAc) at the nonreducing end. Surprisingly, these GnTI-dependent N-glycans were also found to be modified with (di)methylated hexose. The identification of GnTI-dependent N-glycans in combination with N-glycan methylation in B. braunii revealed an uncommon type of N-glycan processing in this microalgae.

Keywords: Botryococcus braunii; N-glycosylation; gene ontology annotation; mass spectrometry; post-translational modification.

MeSH terms

  • Glycopeptides / metabolism
  • Glycoproteins / chemistry
  • Glycoproteins / metabolism
  • Glycosylation
  • Methylation
  • Microalgae / enzymology*
  • N-Acetylglucosaminyltransferases / metabolism*
  • Oxygen Isotopes
  • Polysaccharides / chemistry
  • Polysaccharides / metabolism*


  • Glycopeptides
  • Glycoproteins
  • Oxygen Isotopes
  • Polysaccharides
  • N-Acetylglucosaminyltransferases
  • UDP-GlcNAc alpha-D-mannoside beta-1,2-N-acetylglucosaminyltransferase