TYchi, a novel chitinase with RNA N-glycosidase and anti-tumor activities.

Chitinases which catalyze hydrolysis of chitin are believed to be antifungal proteins in plant. Nevertheless, a variety of functions and some new enzymatic activities of chitinases have been found in recent years. We cloned a novel protein from Trichosanthes kirilowii Maximowicz (Family Cucurbitaceae) named TYchi. Expression of TYchi gene in T. kirilowii plants was induced by F. oxysporum, an important cucurbitaceous fungal pathogen, which indicated that TYchi involved in the pathogen-induced plant defense reaction. In addition to its chitin-hydrolytic activity, the recombinant TYchi protein also had RNA N-glycosidase property. In cell-free rabbit reticulocyte lysate system, TYchi inhibited protein synthesis with an IC50 of approximate 5 nM. TYchi also exhibited efficient cytotoxicities to leukemia U937 and choriocarcinoma JAR cells with IC50 about 54 microg ml(-1) and 73 microg ml(-1), respectively. Structure analyses indicated that the putative domain of TYchi is highly similar to the well known active domain of the N-glycosidase trichosanthin (TCS). This bifuntional protein should be useful in diverse applications like RIP-based immunotoxin agent and genetic engineering of plant resistance.