A robust cysteine-deficient chitinase-like antifungal protein from inner shoots of the edible chive Allium tuberosum

From the inner shoots of the chive Allium tuberosum, a single-chained prote in with a molecular weight of 36 kDa and an N-terminal sequence manifesting resemblance to chitinases but lacking in cysteine residues characteristic of a cysteine-rich domain present in chitinases of other Allium species, wa s purified. The isolation procedure entailed affinity chromatography on Aff i-gel blue gel, ion-exchange chromatography on DEAE-cellulose and pro-Mono S, and gel filtration on Superdex 75. The protein was unadsorbed on DEAE-ce llulose and adsorbed on Affi-gel blue gel and Mono S. It exhibited antifung al activity against Rhizoctonia solani, Fusarium oxysporum, Coprinus comatu s, Mycosphaerella arachidicola, and Botrytis cinerea. The IC50 for its anti fungal effect against Botrytis cinerea was 0.2 muM. The antifungal activity was stable after 1 h at pH 1.6 and 12.3, and up to 60 degreesC for 5 min. Incubation of the protein with trypsin or chymotrypsin at an enzyme:substra te ratio of 1:100 and pH 7.6 up to 150 min did not affect its antifungal ac tivity. The protein did not exhibit antibacterial activity. The protein inh ibited cell-free translation in a rabbit reticulocyte system with an IC50 o f 0.8 muM, but did not affect the proliferation of mouse splenocytes. It ex erted some cytotoxic effect on breast cancer cells and was inhibitory towar d HIV-1 reverse transcriptase. (C) 2000 Academic Press.