(German title: Suche nach und Verwendung von Enzymen marinen Ursprungs zur gezielten Hydrolyse sulfatierter Polysaccharide)

In the search for alternative sources of substances with high bioactivity and fewer undesirable side effects, the focus is increasingly on substances from nature. The oceans are an interesting source of biologically active compounds due to their high biodiversity and almost inexhaustible resources. One of these substances, which is extracted from marine brown algae, is fucoidan. Fucoidan is a sulphated structural polysaccharide that is found in the amorphous fraction of the cell wall of brown algae and has promising applications as a drug or functional food. Fucoidans have been shown to have antiviral and antibacterial properties. 

Fucoidan from the brown algae Fucus vesiculosus is an α-1,3-1,4 linked high molecular weight polysaccharide, mainly consisting of the monosaccharide fucose. The sulphate esters located at positions 2, 3 or 4 are essential for bioactivity. For intracellular, e.g. anti-inflammatory effects, it is necessary that these polysaccharides are present in smaller molecular weights as only then is transport or diffusion through the membrane possible. Acid hydrolysis to reduce the molecular weights of sugars is not advisable in the case of sulphated polysaccharides, as the effect of heat in low pH ranges leads to the cleavage of the sulphate esters and thus to an impairment of bioactivity.

The method of choice for the gentle hydrolysis of fucoidans is the use of specific enzymes. Although these so-called fucosidases or fucoidanases are also components of terrestrial flora and fauna, they are mainly found in marine bacteria and fungi that live in the habitat of algae. Attempts at whole-cell transformation of fucoidans showed only low enzyme activities. Furthermore, the growth rates of the marine organisms are unsatisfactory. The preferred further procedure is therefore the recombinant expression of these enzymes in E. coli. Through literature research and sequence alignment with published fucosidase genes, the fucosidases from the bacteria M. fucanivorans, S. erythraea and P. atlantica T6c were selected for heterologous expression. The purification of the histagged enzymes is carried out by metal chelate chromatography. The characterisation of the enzymes with regard to activity and chemical properties is just as important as structural investigations.