Characterization of Chitinase from White-Rot Fungus Irpex lacteus NK-1.

Chitin is a cell wall structural component of many fungi and is important for mycelium growth. Therefore, enzymes like chitinase which break down chitin, are likely important in fungi during morphological changes. Irpex lacteus, a white-rot fungus isolated from wood-rotting fungi, produces several chitinases. Although it produces a range of chitinases, there are currently no characterization reports exploring them, despite the interest and body of published works evaluating carbohydrate degrading enzymes. In this study, IlChi18C was cloned and recombinantly produced using Pichia pastoris as a host. Properties of purified IlChi18C were determined, revealing an optimal pH of 5.0 and temperature of 50 °C when using pNP-N,N'-diacetyl-β-D-chitobioside (pNP-(GlcNAc)₂) as a substrate. It is activated in the presence of metal ions such as Mg²⁺, Ca²⁺, and Mn²⁺, but inhibited by DMSO, EtOH, and SDS. The Km and Vmax of IlChi18C for this substrate are 3.48 mM and 5.46 µM min^-1, respectively. Using pNP-(GlcNAc)₂ and chitin powder as substrates, IlChi18C predominantly exhibited exo-type chitinase activity, releasing chitobiose from the non-reducing ends of chitin chains. It was also observed that this enzyme acts on the fruiting body of Flammulina velutipes, releasing chitobiose as the main product.