A chitosanase from Paecilomyces lilacinus with binding affinity for specific chito-oligosaccharides

Abstract

A purple-spore, rhizosphere-inhabiting nematophagous fungus, further identified as Paecilomyces lilacinus, was found to grow on chitosanase-detecting plate. An induced endochitosanase having a molecular mass of 23 kDa was purified from the culture medium by a single cation-exchange column-chromatography step. Its optimum pH, optimum temperature and pi were found to be 6.0, 50 degrees C and 8.3 respectively. The N-terminal amino acid sequence of the purified enzyme was partially determined. On the basis of the partial sequence XQLPANLXXIYD and the BLAST results, the purified chitosanase was classified as a new member of the family 75 glycohydrolases. Complete hydrolysis of 95% deacetylated chitosan by the isolated chitosanase released chitotriose, chitotetraose and chitopentaose as the major hydrolytic products. Two oligosaccharides, which were further determined to be GlcN-GlcN-GlcNAc and GlcNAc-GlcN-GlcN-GlcNAc by chemical methylation followed by liquid chromatography-tandem MS analysis, were obtained after the denaturation of the purified chito-sanase. This is the first documented finding that chitosanase can be produced in a Paecilomyces strain and that it has binding affinity for specific N-acetylated oligosaccharides.