Chitosanase catalyzing the endo-type cleavage of chitosan, the deacylated form of chitin. Chitosanase may be crucial in the degradation of the deacetylated portion of chitin in the fungal cell wall. Chitoolisaccharides produced by the hydrolysis of partially N-acetylated chitosan are known to have many biological activities, including antibacterial activity, immune-enhancing effects, and elicitor activity. Endohydrolysis of beta-(1->4)-linkages between D-glucosamine residues in a partly acetylated chitosan. Optimum pH is 5.5. Optimum temperature is 50 degrees Celsius. The C-terminal R3 domain contains 3 tandem repeats required for the binding to insoluble chitosan. Belongs to the glycosyl hydrolase 75 family.