Paper accepted: “A chitin deacetylase of Podospora anserina has two functional chitin binding domains and a unique mode of action”
Today, Janina Hossbach’s and her co-authors paper on characterisation of the first chitin deacetylase with two chitin binding modules was accepted for publication in “Carbohydrate Polymers”. In spite of their name, chitin deacetylases (CDA) do not act on chitin, at least not on chitin polymers as these form insoluble crystals. Early on, we had dreamed of engineering a CDA by fusing it with a chitin binding module borrowed from a chitinase active on crystalline chitin. However, in spite of years of trying, this did not succeed. We had also identified genes which looked like they might be coding for CDA with chitin binding domains, but when Janina expressed them heterologously, they had no CDA activity, not even on chitin oligomers. For her doctoral project, she then had a different idea: she compared the catalytic domains of all putative CDA genes which have chitin binding domains with the catalytic domains of the few experimentally proven CDAs - and she found a single one that would cluster with the proven ones. This one she expressed in the yeast Hansenula polymorpha, with the help of Andreas Kranz from the company Artes Biotechnology. And the recombinant enzyme was active as a CDA, even - if only to a minor extent - on chitin polymers! And Franziska Bußwinkel then showed in her Master thesis that deleting one or both of the chitin binding modules decreased this activity significantly. This is not yet the activity that will allow a biotechnological conversion of chitin into chitosan, but it is a ray of hope that one day, we will get there.