Chitosans, partially N-acetylated polyglucosamines, are perhaps the most promising and most versatile functional biopolymers. Chitosans are a family of biomolecules differing in their degree of polymerisation (DP), degree of acetylation (DA), and pattern of acetylation (PA), and these factors have been shown (DP, DA) or are likely (PA) to influence their material properties and biological functionalities. Commercially available chitosans are derived by chemical processes from chitin typically sourced from crab or shrimp shell wastes. While DP and DA can be controlled rather well in these processes, the chitosans obtained invariably have random PA. In contrast, natural chitosans which are known to occur in some fungal cell walls are thought to be synthesised from chitin by the action of chitin deacetylases. Such natural chitosans have not been analysed in detail, and the fungal chitin deacetylases have proven difficult to obtain as recombinant enzymes. Recently, we have been successful in heterologously expressing a few fungal chitin deacetylase genes in different prokaryotic and eukaryotic expression systems, yielding active recombinant enzymes for detailed characterisation of their substrate specificities and of their products. Interestingly, we found that of the three chitin deacetylases analysed in detail so far differed in both aspects, yielding oligomeric and polymeric chitosans as products which differ in their pattern of acetylation. When fully acetylated chitin oligomers are used as substrates, the enzymes yield partially acetylated chitosan oligomers with different, defined sequences of acetylated and deacetylated residues, as revealed by mass spectrometric sequencing. Fully acetylated chitin polymers were poor substrates for the enzymes, but partially acetylated chitosan polymers with high DA (and random PA) were good substrates for all three chitin deacetylases which, however, were not able to fully deacetylate them. When we analysed the PA of the resulting chitosan polymers with low DA using enzymatic / mass spectrometric fingerprinting, they turned out to differ in their PA. While one of the enzymes yields a...<br/><br/>

Enzymatic control of the acetylation pattern in chitosans

253rd National Meeting (2017)

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