Novel approach for developing designer chitosans 

R Singh, T Weikert and BM Moerschbacher        

Department of Plant Biochemistry and Biotechnology, Westphalian Wilhelms-University Münster, Schlossplatz 8, 48143 Münster, Germany

Chitosans, a family of partially de-N-acetylated derivatives, are identified as one of the most versatile and most promising functional biopolymers in various bio-activities. Nevertheless, the commercial exploitation of chitosans still lags behind due to poor reproducibility.
It is hypothesized that the biological activities of partially acetylated chitosans crucially depend on the physico-chemical properties of the oligomer. Accordingly, our goal of the present work was to define the mechanism of chitosan oligomers production by using chitosan hydrolyzing enzymes such as chitosanases, at the structural level. 
To this approach, combined in silico and in vitro methods were applied to predict the recognition properties occurring between chitosan and chitosanase. The putative subsite specificity was determined for the acetylated and deacetylated subunits of chitosan oligomers.
In the absence of crystallographic structure of the substrate bound chitosanase from Bacillus sp. MN, a 3D structure was determined by homology modeling. Binding sites were characterized for the prediction of possible subsites and corresponding residues present in the enzyme. In addition, the binding mode, possible interactions and putative subsite specificity for the acetylated and deacetylated subunits were inferred between chitosan and chitosanase. These calculations were based on docking studies of partially acetylated chitin oligomers with varying pattern, degree of acetylation and size. Based on this analysis, putative functionally important residues for defining the binding pattern of chitosan oligosaccharides were predicted. Our results will be useful for guiding the bio-engineering of this chitosanase for the production of designer chitosans with a more specific pattern of acetylation and defined functions.