The structure of fucoidan by linkage analysis tailored for fucose in four algae species: Fucus serratus, Fucus evanescens, Fucus vesiculosus and Laminaria hyperborea

Linkage analysis after permethylation allows the determination of the linkage patterns between monomers in complex polysaccharides. Fucoidan is a heteropolysaccharide found in algae that is derivatised with sulphate groups. We recently improved the methodology for the linkage analysis in fucoidan with a focus on fucose. Critical improvements were done in reaction conditions, reagents, isolation of the polymer, and the optimisation of the chromatographic separation. In this study, we employ this enhanced method to the fucoidans of Fucus serratus (FSR), Fucus evanescens (FE), Fucus vesiculosus (FV) and Laminaria hyperborea (LH). This shed new light on the diversity found in fucoidans and the capabilities of the method. The fucoidans were found to be very varied, with a degree of sulphation from 0.26 to 0.73. The sulphate content as determined by the linkage analysis agreed well with the barium sulphate method, which tended to underestimate higher sulphate contents. Sulphate groups were present in positions 3 and 4, 2 and 4, and exclusively 2, but never in all three possible positions. Glycosidic linkages were found in all possible positions, with 3 as the more common one. Branching occurs in all linkage-combinations, and only F. vesiculosus featured a sulphate substituent at a branching point.