Mocsai, R. | bioRxiv Science

bioRxiv2024

The wondrous and worrying diversity of the N-glycans of Chlorella food supplements

N-glycans have recently emerged as highly varied elements of Chlorella strains and products. Four years and many samples later, the ever-growing N-glycan diversity shall be revisited in the light of concepts of species definition and product authenticity. N-glycans of commercial products were analyzed by matrix-assisted time-of-flight mass spectrometry (MALDI-TOF MS) supported by chromatography on porous graphitic carbon with mass spectrometric detection. While 36% of 172 products were labeled C. vulgaris, only few had matching N-glycan patterns. 5 and 20 % of the products matched with C. sorokiniana strains SAG 211-8k and SAG 211-34, respectively, which, however, carry entirely different structures. 41 % presented with four frequently occurring glyco-types while 26 % of the samples showed unique or rare N-glycan patterns. The rest presented what could be taken as a C. vulgaris type N-glycan pattern. Identical masses derive from different structures in many cases. By no means do we want to question the presumed health benefits of the products or the honest intentions of manufacturers. We rather wish to raise awareness for the fascinating but also worrying variety of microalgal N-glycans and suggest it as a means for defining product identity and taxonomic assignments.

plant biology↗

bioRxiv2021

O-methylated N-glycans Distinguish Mosses from Vascular Plants

In the animal kingdom, a stunning variety of N-glycan structures has emerged with phylogenetic specificities of various kinds. In the plant kingdom, however, N-glycosylation appears as strictly conservative and uniform. From mosses to all kinds of gymno- and angiosperms, land plants mainly express structures with the common pentasaccharide core substituted with xylose, core 1,3-fucose, maybe terminal GlcNAc residues and Lewis A determinants. In contrast, green algae biosynthesize unique and unusual N-glycan structures with uncommon monosaccharides, a plethora of different structures and various kinds of O-methylation. Mosses, a group of plants that are separated by at least 400 million years of evolution from vascular plants, were hitherto seen as harbouring an N-glycosylation machinery identical to that of vascular plants. To challenge this view, we have analysed the N-glycomes of several moss species using MALDI-TOF/TOF, PGC-MS/MS and GC-MS. While all species contained the plant-typical heptasaccharide with no, one or two terminal GlcNAc residues (MMXF, MGnXF and GnGnXF, respectively), many species exhibited MS signals with 14.02 Da increments as characteristic for O-methylation. Throughout all analysed moss N-glycans the level of methylation differed strongly even in the same family. In some species, methylated glycans dominated, while others had no methylation at all. GC-MS revealed the main glycan from Funaria hygrometrica to contain 2,6-O-methylated terminal mannose. Some mosses additionally presented very large, likewise methylated complex-type N-glycans. This first finding of methylation of N-glycans in land plants mirrors the presumable phylogenetic relation of mosses to green algae, where O-methylation of mannose and many other monosaccharides is a common trait.

biochemistry↗