What are chitosanases?
Chitosanases are hydrolytic enzymes able to cleave the β-1,4-glycosidic bond between two glucosamine residues (GlcN-GlcN). Some chitosanases can also cleave the GlcNAc-GlcN and/or the GlcN-GlcNAc bond, but they do not cleave the GlcNAc-GlcNAc bond. Hence, chitosanases can depolymerise chitosan polymers and oligomers, including poly- and oligoglucosamines, but not chitin. Chitosanases have the Enzyme Commission number EC 220.127.116.11, and they belong to a number of different Glycoside Hydrolase (GH) families according to the CAZY classification of Carbohydrate Active enZYmes, including GH8 and GH46. Initially, chitosanases were divided into three, then four classes according to their cleavage specificities, where class I chitosanases would cleave GlcN-GlcN and GlcNAc-GlcN, class II only GlcN-GlcN, class III GlcN-GlcN and GlcN-GlcNAc, and class IV all three linkages, but a recent reassessment showed that this classification is too simplified: none of the enzymes analyzed possessed true class II specificity, while all of them required a GlcN unit at the (-2) subsite, i.e. two units "upstream" of the cleavage site. Naturally occuring chitosanases appear to be exclusively endo-acting enzymes, and their processivity is not known.