What are chitin de-N-acetylases?
Chitin de-N-acetylases convert the GlcNAc unit in chitin and chitosan polymers and oligomers into GlcN units by hydrolyzing the amide bond between glucosamine and acetate. Chitin deacetylases have the Enzyme Commission number EC 220.127.116.11, and they belong to the Carbohydrate Esterase (CE) family CE4 according to the CAZY classification of Carbohydrate Active enZYmes. Despite their name, chitin deacetylases barely act on polymeric, crystalline chitin, probably only deacetylating the surface of the crystals. The presence of chitin binding domains in some deacetylases appear to increase this activity somewhat but not to the point of yielding acid-soluble chitosan. They do act on chitosans with a high degree of acetylation, converting them to chitosans of low degree of acetylation, but not deacetylating them fully to polyglucosamines. It has been speculated that the chitosan so produced might have a non-random pattern of acetylation, in contrast to all commercially available chitosans which are produced by partial chemical deacetylation of chitin or by partial chemical re-N-acetylation of polyglucosamine and, therefore, invariably have random patterns of acetylation. Chitin deacetylases also work well on chitin oligomers where they often show marked regio-selectivity, deacetylating some but not all GlcNAc units to GlcN. In this way, different chitin deacetylases produce different chitosan oligomers. The enzymes can even be used in reverse mode to N-acetylate GlcN oligomers, retaining their regio-selectivity. In this way, it has been possible to produce all fourteen possible partially acetylated chitosan tetramers. In conjunction with chitin synthase genes, chitin deacetylase genes can be used to drive the biotechnological in vivo synthesis of defined monoclonal chitosan oligomers in cell factories.