A pseudo-phytochelatin synthase in the ciliated protozoan Tetrahymena thermophila

摘要

Phytochelatins (PCs) and metallothioneins (MTs) are the two major heavy metal chelating peptides ineukaryotes. We report here on the identification of a biosynthetically inactive pseudo-phytochelatin synthaseenzyme (TNIPCS) in the ciliate Tetrahymena thermophila, the first of this kind (pseudo-PCS) to be describedin eukaryotes. Tt*PCS which resembles a true PCS at the N-terminal region, while it is most divergent in itsCys-poor C-terminal region, was found to be up-regulated under cadmium stress conditions. However onlyglutathione (GSH) hydrolysis products, but not PCs, could be detected in extracts from Cd-treated cells. Thelatter feature is reminiscent of pseudo-PCS enzymes recently identified in cyanobacteria, which are alsobiosynthetically inactive, but capable to hydrolyze GSH.