Biology subjects

Altmann, F.

Publications and source records attributed to Altmann, F..

9 recordsLinked to original sources

bioRxiv2025

Niche partitioning by resource size in the gut microbiome

Niche partitioning promotes diversity of the human gut microbiota. However, the molecular basis of resource specialization and niche separation in the gut remains poorly understood. Here we show that structural differences in glycan transporters drive members of the genus Bacteroides, common human gut commensals, to specialize on distinct chain lengths of the same fructan molecule. While species encoding canonical SusCD systems for glycan import -formed by a membrane-embedded barrel capped with a lipoprotein lid- specialized in long-chain fructans, species with smaller lidless transporters, not previously described in Bacteroides, specialized in short-chain fructans. Strikingly, we found that a [~]140-amino acid domain in the SusC barrel is a structural feature that governs substrate preference: deleting it does not impair transport but instead shifts uptake preferences from long-to short-chain fructans. These structural differences predict competitive outcomes in vivo on fructans of varying lengths, suggesting that glycan uptake mechanisms shape ecological niches in the gut and can inform fiber-based dietary interventions. Similar small lidless transporters exist across the Bacteroidota, expanding the paradigm of glycan utilization in this phylum beyond the canonical SusCD architecture.

microbiology↗

bioRxiv2024

Adaptation and acclimation of gametophytic traits to heat stress in a widely distributed wild plant along a steep climatic gradient

O_LIClimate change-induced heat waves often result in reduced seed yields and quality via high-temperature effects in the gametophytic phase. Surprisingly, the ability of pollen and ovules, particularly among wild plant populations, to adapt or acclimate to heat stress remains poorly understood. C_LIO_LITo address this gap, we examined the adaptive and acclimation potential of six gametophytic traits in eleven distinct populations of wild Silene vulgaris across a temperature gradient in Europe. First, we cultivated plants in a common garden to reveal differences in gametophytic traits indicative of adaptation. Next, we assessed the acclimation potential of these traits to heat stress by subjecting flowering plants to two chronic heat stress (CHS) treatments: moderate (35/30 {degrees}C) and severe (40/35 {degrees}C), for 18 days. C_LIO_LIFindings from the common garden experiment indicated no intraspecific variation in gametophytic traits across the temperature gradient, suggesting that these traits may not influence the plants sexual adaptation to its local habitat. Plants originating from colder climates produced more and larger seeds than those from warmer climates. During CHS treatments, the female gametophyte was less temperature sensitive compared to the male gametophyte. Moderate CHS led to larger ovaries with more, large-sized ovules, while severe CHS reduced ovule numbers but increased their size. In contrast, both CHS treatments decreased pollen grain numbers, size, and anther length, with severe CHS causing more significant reductions. These reductions in gametophytic traits ultimately translated to lower seed yield and quality, which may threaten the sustained existence of natural plant populations over time. Under both CHS treatments, the acclimation potential did not vary among plant populations along the temperature gradient, except for pollen size under severe CHS, with larger pollen size in warmer climates than in colder regions. C_LIO_LIOur findings suggest that the lack of adaptation and acclimation mechanisms in the gametophytic traits (except for pollen size) of wild Silene vulgaris populations along the temperature gradient indicates that these plants may rely on alternative strategies, such as shifts in flowering time, to respond to thermal stress. C_LI

plant biology↗

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↗

bioRxiv2022

The Mouse N-Glycome Atlas - High-resolution N-glycan analysis of 23 mouse tissues.

N-glycosylation is one of the most common protein modifications in eukaryotes, with immense importance at the molecular, cellular, and organismal level. Accurate and reliable N-glycan analysis is essential to obtain a systems-wide understanding of fundamental biological processes. Due to the structural complexity of glycans, their analysis is still highly challenging. Here we make publicly available a consistent N-glycome dataset of 20 different mouse tissues and demonstrate a multimodal data analysis workflow that allows for unprecedented depth and coverage of N-glycome features. This highly scalable, LC-MS/MS data-driven method integrates the automated identification of N-glycan spectra, the application of non-targeted N-glycome profiling strategies and the isomer-sensitive analysis of glycan structures. Our delineation of critical sub-structural determinants and glycan isomers across the mouse N-glycome uncovered tissue-specific glycosylation patterns, the expression of non-canonical N-glycan structures and highlights multiple layers of N-glycome complexity that derive from organ-specific regulations of glycobiological pathways.

biochemistry↗

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↗

bioRxiv2021

Better together - Relative retention time plus spectral matching improves automated glycan characterization using PGC-nLC-IT-ESI-MS/MS

Porous Graphitized Carbon nano-liquid chromatography tandem mass spectrometry (PGC-nLC-MS/MS) is a glycomics technique with the unique capacity to differentiate isobaric glycans. The lack of suitable software tools integrating chromatography and MS-information delivered by PGC-nLC-MS/MS has been limiting fast and robust glycan identification and quantitation. We report a LC-system-independent strategy called GlycoRRT that combines relative retention time (RRT) and negative ion fragment spectra analyses for isobaric structure-specific glycomics of PGC-nLC-MS/MS data. The GlycoRRT toolset is fully customizable and easily adaptable enabling semi-automated high-throughput structural assignments. The current library contains over 200 entries and their individual meta-data (MS instrumentation, experimental conditions, retention times, fragmentation profiles and glycan structural diagnostic ion features) relevant for reliable data analyses. The GlycoRRT workflow was employed to map the N- and O-glycome in blood group matched human plasma and urine as well as decipher Immunoglobulin (IgG) glycosylation features from 13 different animal species. We have also developed visualization tools to enable a consistent, reliable, and reproducible analysis of large sets of multidimensional PGC-nLC-MS/MS glycomics data. This comprehensive glycan resource provides the glycan map of human and animal species, will serve as a reference in dissecting the role of glycans in host pathogen interaction and zoonotic disease transmission.

biochemistry↗

bioRxiv2021

Time grid-based isomer specific N-glycan analysis and detection of bisecting Lewis X in human brain

The importance of protein glycosylation in the biomedical field demands for methods capable of resolving and identifying isomeric structures of N-glycans. However, the unambiguous identification of isomeric structures from complex mixtures is currently not reasonably realized even by the most sophisticated approaches. Here we present a novel approach which uses stable isotope labelled reference N-glycans to establish a retention time grid (glyco-TiGr) on porous graphitized carbon. This furthermore enables retention as the primary criterion for the structural assignment of isomeric N-glycans. Moreover, we biosynthesized forty natural isomers of the fundamental N-glycan type consisting of five hexoses, four N-acetylhexosamines and one fucose residue. Nearly all of these isomers occupied unique positions on the retention time grid. Reference glycan assisted retention time determination with deci-minute accuracy narrowed the assignment space to very few, often only one possible glycan isomer. Application of the glyco-TiGr approach revealed yet undescribed isomers of Lewis x determinants in multimeric human IgA and hybrid type N-glycans in human brain with galactose and even fucose linked to the bisecting N-acetylglucosamine. Thus, the brain N-glycome displayed a degree of sophistication commensurate with this organs role.

biochemistry↗

bioRxiv2021

Identification of lectin receptors for conserved SARS-CoV-2 glycosylation sites

New SARS-CoV-2 variants are continuously emerging with critical implications for therapies or vaccinations. All 22 N-glycan sites of SARS-CoV-2 Spike remain highly conserved among the variants B.1.1.7, 501Y.V2 and P.1, opening an avenue for robust therapeutic intervention. Here we used a comprehensive library of mammalian carbohydrate-binding proteins (lectins) to probe critical sugar residues on the full-length trimeric Spike and the receptor binding domain (RBD) of SARS-CoV-2. Two lectins, Clec4g and CD209c, were identified to strongly bind to Spike. Clec4g and CD209c binding to Spike was dissected and visualized in real time and at single molecule resolution using atomic force microscopy. 3D modelling showed that both lectins can bind to a glycan within the RBD-ACE2 interface and thus interferes with Spike binding to cell surfaces. Importantly, Clec4g and CD209c significantly reduced SARS-CoV-2 infections. These data report the first extensive map and 3D structural modelling of lectin-Spike interactions and uncovers candidate receptors involved in Spike binding and SARS-CoV-2 infections. The capacity of CLEC4G and mCD209c lectins to block SARS-CoV-2 viral entry holds promise for pan-variant therapeutic interventions.

molecular biology↗

bioRxiv2020

Stable Protein Sialylation in Physcomitrella

Recombinantly produced proteins are indispensable tools for medical applications. Since the majority of them are glycoproteins, their N-glycosylation profiles are major determinants for their activity, structural properties and safety. For therapeutical applications, a glycosylation pattern adapted to product and treatment requirements is advantageous. Physcomitrella (Physcomitrium patens, moss) is able to perform highly homogeneous complex-type N-glycosylation. Additionally, it has been glyco-engineered to eliminate plant-specific sugar residues by knock-out of the {beta}1,2-xylosyltransferase and 1,3-fucosyltransferase genes ({Delta}xt/ft). Furthermore, P. patens meets wide-ranging biopharmaceutical requirements such as GMP compliance, product safety, scalability and outstanding possibilities for precise genome engineering. However, all plants, in contrast to mammals, lack the capability to perform N-glycan sialylation. Since sialic acids are a common terminal modification on human N-glycans, the property to perform N-glycan sialylation is highly desired within the plant-based biopharmaceutical sector. In this study, we present the successful achievement of protein N-glycan sialylation in stably transformed P. patens. The sialylation ability was achieved in a {Delta}xt/ft moss line by stable expression of six mammalian coding sequences combined with targeted organelle-specific localization of the encoded enzymes responsible for synthesis, activation, transport and transfer of sialic acid. Production of free and (CMP)-activated sialic acid was proven. The glycosidic anchor for the attachment of terminal sialic acid was generated by the introduction of a chimeric human {beta}1,4-galactosyltransferase gene under the simultaneous knock-out of the gene encoding the endogenous {beta}1,3-galactosyltransferase. Functional complex-type N-glycan sialylation was confirmed via mass spectrometric analysis of a stably co-expressed recombinant human protein.

bioengineering↗