Schweder, Thomas
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Schweder, Thomas
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Schweder, Thomas
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Item-typ:Veröffentlichung, Diatom mannan – a sulfated glycan shapes surface ocean microbiomes(2024-11-28); ; ; Diatoms account for 20% of global photosynthesis and secrete up to 50% of their primary products as glycans. The fate of these glycans influences global ocean carbon budgets and exerts substantial selection pressure on the surrounding microbiome. However, current knowledge about secreted diatom glycans is restricted to monosaccharide composition analyses and lacks information regarding glycan configuration, connectivity, and additional modifications such as sulfation. In this dissertation, I describe an anion-exchange chromatography-based approach to isolate a pure anionic mannan from the culture supernatant of a marine diatom. A combination of techniques solved the structure of a sulfated mannan. Microbial growth analyses showed that the mannan serves as a food source for specialized marine bacteria that were identified and isolated during diatom blooms. The genomes of these isolates contained a previously identified gene cluster rich in mannanases and sulfatases. Using heterologous expression, I solved the bacterial degradative cascade for the mannan, which comprised three enzymes that hydrolyzed the mannan in four catalytic steps. The enzymes within the cascade included a novel glycoside hydrolase family and activities for a previously undescribed sulfatase subfamily. Furthermore, an α-mannosidase is the first member within its family that degrades sulfated mannan oligosaccharides. I further exploited the specificity of these enzymes to develop a tool to quantify the glycan in complex mixtures such as seawater. Metagenomic analyses of the TARA Oceans circumnavigation dataset revealed a global abundance of mannan PUL-harboring bacteria, indicating that the mannan modulates microbiomes globally.Dissertation149 151 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Re-entrant phase separation of fucoidan-protein systemResearch of fucoidan beholds an extraordinary complexity and singularity in fucoidan from structure to function. Structurally, fucoidan cannot be portrayed by one simple description without missing other meaningful features of the glycan. Functionally, fucoidan is to be consumed by bacteria, but a resistance to microbial degradation is what it is known for. Alongside with many medicinal potentials, fucoidan exhibits even more ambiguous effects on cells and organisms. In order to decompose the behavioral dissonances of fucoidan, this doctoral thesis delves into the mechanistic component of its functionality, particularly the molecular interactions that fucoidan enmeshes in as an anionic polyelectrolyte. With a composite of experimental approaches comes the multivalent bindings of fucoidan toward diverse proteins, featuring a formation of fucoidan-protein complexes. The non-linearity and the concentration-dependency of this complexing interaction denote a re-entrant phase separation that effectively explain for the puzzling observations in fucoidan bioactivities. Not only does the discovery provide the contextual framework for future research on fucoidan and other polysaccharides of similar chemistry, but it also is the molecular mechanism that transcends the role of an algal cell-wall glycan. Utilizing the very complexity and singularity of its own and of the surroundings, fucoidan interacts with, protects and sustains the ecosystem it is in.Dissertation65 58