The Structural Difference of Isobaric -Glycans of Two Microalgae Samples Reveals Taxonomic Distance.

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