Purification and properties of extracellular chitinases from the parasitic fungus Isaria japonica

Abstract

Two chitinases (P-1 and P-2) induced with colloidal chitin were purified from the culture supernatant of Isaria japonica by chromatography on DEAE Bio-Gel, chromatofocusing and gel filtration with Superdex 75 pg. The enzymes were electrophoretically homogeneous and estimated to have a molecular mass of 43,273 (±5) for P-1 and 31,134 (±6) for P-2 by MALDI-MS. The optimum pH and temperature was 3.5–4.0 and 50°C for P-1 and 4.0–4.5 and 40°C for P-2. P-1 acted against chitosan 7B (degree of deacetylation, 65–74%) = glycol chitin > colloidal chitin = chitosan 10B (degree of deacetylation, above 99%) and P-2 against chitosan 7B > glycol chitin = chitosan 10B > colloidal chitin in order of activity. The products of hydrolysis of chitin and chitosan hexamer were analyzed by MALDI-MS. The products from the chitin hexamer obtained with P-1 were almost all dimers with only a small amount of trimer whereas those obtained with P-2 were mainly trimers with some dimer and tetramer. No hydrolysis of chitosan hexamer was observed. High homology in the amino-terminal sequence for chitinase P-1 was exhibited by chitinases from Trichoderma harzianum, Candida albicans and Saccharomyces cerevisiae in the range of 48–39%. The highest homology for Chitinase P-2 was shown by an endochitinase from Metarhizium anisopliae of 66%, while 44% homology was exhibited by chitinases of Leguminosae plants.