Artikel
Fucoidan: enzymatic purification and modification
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Veröffentlicht: | 7. Oktober 2020 |
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Gliederung
Text
The cell walls of brown algae consists of different polysaccharides, which are very different from those in the cell walls of terrestrial plants. They contain fucoidan, a polysaccharide made mainly of sulfated fucose residues. The structural diversity of fucoidan is extremely large due to varieties in monosaccharide compositions, different types of glycosidic linkages and the presence of large numbers of non-carbohydrate substituents, like sulfations but also acetylations. Fucoidans have been extensively studied because of their wide range of biological activities, such as anticoagulant, antithrombotic, anticancer, anti-inflammatory and immunomodulatory [1], [2], [3]. No drug though is currently available, due mainly to the heterogeneity of the fucoidans. The bio-activity of fucoidans depend largely on the structure of the fucoidans. The fucoidan fine structure differs between seaweed species and harvest time, but also the extraction method largely affect the structure. By the means of specific cell-wall-degrading enzymes, including cellulases and alginate lyases, the fucoidan can be released from the cell wall in a gentle way, releasing intact fucoidans [4]. The fucoidans can be further purified by ion-exchange chromatography, obtaining fucoidans of high purity, high molecular weight and high sulfate content [4]. For some applications, fucoidans of low molecular size are desirable. This is normally obtained through treatments with acid, resulting in random degradation and likely also loss of sulfates. In contrast, by using highly specific fucoidan degrading endo-fucoidanases, the fucoidans can be specifically degraded, releasing oligosaccharides with known structure and size distribution. Other fucoidan specific enzymes, including sulfatases can also be used to specifically change the fine structure of fucoidans, enabling structure-function investigations. Fucoidan-modifying enzymes, including fucoidanases and sulfatases, might be the best tool for not only determining the fine structures of fucoidans but also to determine the relationship between fucoidan and the biological activities; hence enzymes might be the best way to enable the production of homogenous fucoidan drugs, both through enzyme-assisted purification and modification.
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