AUTHOR=Mócsai Réka , Kaehlig Hanspeter , Blaukopf Markus , Stadlmann Johannes , Kosma Paul , Altmann Friedrich 

TITLE=The Structural Difference of Isobaric N-Glycans of Two Microalgae Samples Reveals Taxonomic Distance

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.643249

DOI=10.3389/fpls.2021.643249

ISSN=1664-462X

ABSTRACT=<p>Microalgae of the <italic>Chlorella</italic> clade are extensively investigated as an environmentally friendly source of renewable biofuels and high-value nutrients. In addition, essentially unprocessed <italic>Chlorella</italic> serves as wholesome food additive. A recent study on 80 commercial <italic>Chlorella</italic> preparations revealed an unexpected variety of protein-linked <italic>N</italic>-glycan patterns with unprecedented structural features, such as the occurrence of arabinose. Two groups of products exhibited a characteristic major <italic>N</italic>-glycan isobaric to the Man<sub>2</sub>GlcNAc<sub>2</sub>XylFuc <italic>N</italic>-glycan known from pineapple stem bromelain, but tandem mass spectrometry (MS/MS) analysis pointed at two types of <italic>N</italic>-glycan different from the bromelain structure, as well as from each other. Here we report the exact structures of these two novel <italic>N</italic>-glycan structures, elucidated by nuclear magnetic resonance spectroscopy and MS/MS, as well as on their phylogenetic context. Despite their humble size, these two <italic>N</italic>-glycans exhibited a very different design with structural features unrelated to those recently described for other <italic>Chlorella</italic>-clade strains. The major glycans of this study presented several novel structural features such as substitution by arabinose or xylose of the internal <italic>N</italic>-acetylglucosamine, as well as methylated sugars. ITS1-5.8S-ITS2 rDNA barcode analyses revealed that the xylose-containing structure derived from a product primarily comprising <italic>Scenedesmus</italic> species, and the arabinose-containing glycan type related to <italic>Chlorella</italic> species (SAG211-34 and FACHB-31) and to <italic>Auxenochlorella</italic>. This is another example where characteristic <italic>N</italic>-glycan structures distinguish phylogenetically different groups of microalgae.</p>