Paper published: “Reassessment of chitosanase substrate specificities and classification
Tobias Weikert’s and his co-authors’ paper on a new classification system for chitosanases based on their substrate specificities has been published today in “Nature Communications”. This paper is a direct follow-up of Stefan Cord-Landwehr’s paper on quantitative mass spectrometric sequencing of chitosan oligomers which allows the characterisation of subsite specificities in chitosan hydrolases with an unprecedented accuracy. Anne Niehues contributed the script that allows to analyse the wealth of mass spectrometric data in seconds that previously required weeks of painstaking manual work, and with much more precise results. Finally, and amazingly, Margareta Hellmann proved - during her Bachelor ! thesis supervised by Stefan - that the method is also applicable and useful for the characterisation of pectin hydrolytic enzymes, giving the final kick to our manuscript. Chitosanases had previously been classified in groups I, II, and III, based on assumed absolute specificities of their (-1) and (+1) subsites for acetylated GlcNAc or non-acetylated GlcN units in the chitosan substrate. Tobias now showed that (i) the subsites have relative preferences for these units rather than absolute specificities, and (ii) subsites (-2) and (-2) also have such preferences influencing the hydrolytic specificity of the enzyme, and subsite (-2) even appears to have the most pronounced substrate specificity. This has significant consequences for the use of these enzymes in the biotechnological production of defined chitosan oligomers which due to their part cationic, part hydrophobic nature are promising candidates for many applications, e.g. as plant protectants, prebiotic food and feed ingredients, antibiotic replacements, anti-tumour agents, and many more.