Major Antifungal Activity from the Bulbs of Indian Squill Urginea indica Is a Chitinase

摘要

We have identified a chitinase with antifungal activity in the bulbs of the plant Urginea indica (Indian squill)and purified it about 26-fold.The purified preparation contained a M_r 29 kDa protein that was an active growth inhibitor of the fungal pathogens Fusarium oxysporum and Rhizoctonia solani in an in vitro assay.Amino acid sequence analysis of the M_r 29 kDa protein revealed it to be highly homologous to the family 19 glycoside hydrolases,which are known to possess chitinase activity.The U.indica chitinase lacked a cysteine-rich N-terminal domain (characteristic of class I chitinases)and contained a conserved motif indicative of the signature 1 of family 19 glycoside hydrolases.It shared a approx 70% sequence identity with the 26 kDa endochitinase of Hordeum vulgare,a typical class II chitinase of family 19.The five cysteines in the partial sequence of the M_r 29 kDa chitinase were found to be identical in location to five of the seven cysteines present in the catalytic domain of the H.vulgare enzyme.The molecular weight,the lack of an N-terminal cysteine-rich sequence,and the striking identity to the H.vulgare endochitinase suggest that the M_r 29 kDa U.indica protein is a putative class II chitinase.The antifungal activity is presumably mediated through the chitinolytic activity of the M_r 29 kDa protein.