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PolyModE Final results 

 
Peak oil and peak soil, peak water and peak grain – the beginning of the 21st century marks a crucial transition, from an oil-based economy to a bio-based economy, from exploiting fossil resources to using renewable resources. In many areas such as material sciences or energy, this transition to a knowledge-based bio-economy will heavily rely on the large and diverse group of biopolymers. Bio-based renewable energies mostly rely on the degradation of biopolymers, essentially starch and lignocelluloses, and the consumption of their monomeric building blocks to release the energy stored in them during their photosynthetic biosynthesis. Renewable biomaterials, in contrast, typically rely on the production of biopolymers, either by extraction from biological sources or by biotechnological production means, sometimes combining both. Most biopolymer-based biomaterials such as many polysaccharides, lignin, or rubber are most prominently used for their superior structural properties only. Some biopolymers, however, and in particular polysaccharides, also possess functional properties, and these can be at the basis of a broad spectrum of applications, ranging from food sciences and agriculture over cosmetics and pharmaceutics to biomedical
sciences. The potential of such functional biopolymers is evident, as they combine superior material properties with excellent biocompatibility and often highly versatile biological activities, promising advanced applications in many life-science related market fields. However, the potential of polysaccharides is still largely unfulfilled today, mostly as polysaccharides are very demanding both in terms of their chemistry and in terms of their biology. In particular, the typical microheterogeneity, which is a hallmark of natural polysaccharides, is a severe hurdle in establishing reliable structure/function relationships and, eventually, in developing successful applications based on them.
 Natural polysaccharides have evolved to fulfill a plethora of functions in their natural biological context, and as each individual polysaccharide typically fulfills multiple roles, their structures represent a balanced compromise to achieve the best overall performance. This, however, is different in biotechnological applications where the polysaccharide used typically has to fulfill a special singe purpose, so that there is room for improvement over the natural compound. Also, the roles attributed to polysaccharides in biotechnological applications may differ from their natural roles, so that modifications may be required to change
their structural and functional properties. Today, these modifications aiming at improving the performance of a polysaccharide are typically attempted using chemical means, such as acid or alkaline treatment, or the introduction of additional substituents. These chemical methods, while typically well established and easily upscaled to industrial dimensions, often have severe limitations, in particular regarding their specificity. Also, their environmental burden in terms of energy or water consumption, or in terms of toxic waste production, is sometimes high. The PolyModE project, therefore, aimed at developing enzymatic tools to perform such modifications specifically and in an environmentally benign form.
The central assumption of the PolyModE project was that it is the pattern of substitution of complex functional polysaccharides that fine-tune their physico-chemical properties and/or their biological activities. These could be patterns of e.g. acetylation, sulfation, or methyl-esterification, but they could also be patterns in the sequence of monosaccharide building blocks or their glycosidic linkage type, or even patterns in the distribution of different side chains. We predicted that nature uses enzymes to ‘ write’ these patterns, but also to ‘ read’ them, i.e. to specifically and partially degrade the complex polysaccharides to generate specific oligosaccharides as the individual ‘ words’ of the language of sugars. The PolyModE project targeted writing and reading enzymes for the guluronic acid distribution in alginates from red algae (C5-epimerases, lyases), for the pattern of sulfation in carrageenans from brown algae (sulfatases and sulfurylases), for the pattern of acetylation in chitosans from shrimp and fungi (deacetylases and hydrolases) as well as in the pattern of sulfation in human glycosaminoglycans (sulfotransferases and sulfatases), in the patterns of methyl- and acetyl-esterification in pectins from higher plants (acetyl- and methyl-esterases) and in the distribution patterns of acetylated and/or pyruvylated side chains in bacterial xanthan gums (acetyl-esterases, lyases, and hydrolases). These six polysaccharides represent the most important or most promising functional polysaccharides today, with diverse applications of alginates, carrageenans, pectins, and xanthans as functional food ingredients due to their superior material properties, in particular gelling abilities, and with highly promising applications of glycosaminoglycans and chitosans in biomedical fields due to their versatile and highly specific biological activities.
Six work packages were devoted to these polysaccharides and connected through a central work package focusing on the development of generic techniques in bioinformatics and molecular genetics, heterologous expression and fermentation, enzyme characterization and optimization, as well as structural and functional characterization of enzymatically modified polysaccharides.
All seven work packages were highly successful and reached at least one of the two major goals so that in all cases, significant progress beyond the state of the art was achieved. Unfortunately, we were eventually denied a cost-neutral six-month extension of the project which would have allowed us, at no extra cost, to advance these results to the point where they would have been ready to be taken up by industry for further development and integration into their large scale production processes. We now aim at securing alternative funding so that these results will not be lost to European industry and society.
More detailed information in the project final summary