Automated synthesis of fucoidan enables molecular investigations in marine glycobiology

Fucoidan, a sulfated polysaccharide found in algae, occupies a central yet enigmatic role in marine carbon sequestration and exhibits a wide array of bioactivities. However, the inherent molecular diversity and structural complexity of fucoidan hinders precise structure-function studies. To address this, we present a rapid and reproducible automated synthesis method for generating well-defined linear and branched α-fucan oligosaccharides. Our syntheses include oligosaccharides with up to 20 cis-glycosidic linkages, diverse branching patterns, and 11 sulfate monoesters. In this study, we showcase the utility of these glycans by (i) characterizing two endo-acting fucoidan glycoside hydrolases (GH107), (ii) serving as standards for NMR experiments to confirm suggested structures of algal fucoidans, and (iii) developing a fucoidan microarray. This microarray enabled precise screening of the molecular specificity of four monoclonal antibodies targeting fucoidan. Utilizing the antibody BAM2, identified here for its specificity to α-(1→3)-fucoidans featuring 4-O-sulfate esters, we provide evidence that such a fucoidan motif is present in a globally abundant marine diatom, Thalassiosira weissflogii. Automated glycan assembly provides a robust platform for accelerating research in marine glycobiology, offering access to fucoidan oligosaccharides with distinct structures, thereby facilitating advancements in our collective understanding of how fucoidan's structure influences its function.