Characterization of a new family 75 chitosanase from Aspergillus sp. W-2.

A new chitosanase gene of glycoside hydrolase (GH) family 75, csnw2, was cloned from an isolated strain Aspergillus sp. W-2 (CGMCC7018). The mature CsnW2 protein, fused to His-tag at C-terminus, was expressed in Pichia pastoris X-33 and purified with the affinity chromatography of Ni(2+)-NTA. The novel recombinant CsnW2 showed maximal activity with chitosan at pH 6.0 and 55°C. Moreover, it had good pH stability and thermostability at a broad pH range of 3.0-10.0 and a temperature range of 30-70°C, respectively. The enzymatic activity of the CsnW2 could be significantly enhanced by Ca(2+), Mn(2+) and Mg(2+) at a concentration of 1mM, but strongly inhibited by Fe(2+), Zn(2+), Ge(2+), Ni(2+) and Cu(2+) above 1mM. The CsnW2 showed specific hydrolytic activity against chitosan and preferred to hydrolyze chitosan with high degree of deacetylation. The main products of chtiosan (92% deacetylation) were chitosan oligosaccharides (COS) with degree of polymerization (DP) arranging from 2 to 6. Combined with the hydrolysis of COS from DP2 to DP6, CsnW2 was considered to be an endo-acting chitosanase.