Isolation of a thermostable legume chitinase and study on the antifungal activity

Chitinases are listed as one class of pathogenesis-related proteins, and they have become a popular research topic because of their resistance to plant-pathogenic diseases. A chitinase with antifungal activity was isolated from the Canadian cranberry beans (Phaseolus vulgaris). The procedure included extraction, ammonium sulfate precipitation, affinity chromatography on Affi-gel blue gel, CM-Sephadex C-50, and Sephadex G-75. There was an almost 108-fold increase in specific activity of the purified chitinase compared with that of the crude extract. The enzyme exhibited a molecular mass of 30.6 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis both under reducing and non-reducing conditions, indicating that it was a monomeric protein. The pI was determined to be 7.6 by isoelectric-focusing electrophoresis. The optimum pH and the optimum temperature for activity towards N-acetyl-glucosamine was 5.4 and 40-55°C, respectively. It exerted a potent inhibitory action toward fungal species including Botrytis cinerea, Physalospora piricola, Fusarium oxysporum, and Pythium aphanidermatum. The chitinase was thermostable up to 58°C in both enzymatic reaction and antifungal activity. The present findings demonstrated a thermostable chitinase from cranberry beans with potentially exploitable significance.