Re-entrant phase separation of fucoidan-protein system

Research 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.