Characterization of phytochelatin synthase-like protein encoded by alr0975 from a prokaryote, Nostoc sp. PCC 7120 |
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Authors: | Tsuji Naoki Nishikori Shingo Iwabe Osamu Shiraki Kentaro Miyasaka Hitoshi Takagi Masahiro Hirata Kazumasa Miyamoto Kazuhisa |
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Institution: | Environmental Biotechnology Laboratory, Graduate School of Pharmaceutical Sciences, Osaka University, Suita, 1-6 Yamadaoka, Osaka 565-0871, Japan. |
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Abstract: | Phytochelatins (PCs) are well known as the heavy metal-detoxifying peptides in higher plants, eukaryotic algae, fungi, and nematode. In contrast, neither PCs nor PC synthase genes have ever been identified in any prokaryotes. The genome sequences for the cyanobacterium Nostoc sp. PCC 7120 were recently completed and allowed us to identify a gene encoding a PC synthase-like protein, termed alr0975. The predicted product of alr0975 contains the conserved N-terminal domain but not the variable C-terminal domain found in eukaryotic PC synthases. The recombinant alr0975 protein strongly catalyzed the first step of PC synthesis, in which glutathione (GSH) is converted to gamma-glutamylcysteine (gamma-EC), although the protein only weakly catalyzed the second step of PC synthesis, namely the transfer of gamma-EC moiety to an acceptor GSH molecule to form PC(2). These results suggest alr0975 protein may be a more primitive form of the PC synthases found in eukaryotes. |
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Keywords: | Phytochelatins Phytochelatin synthase Nostoc sp PCC 7120 Cyanobacterium Heavy metal γ-Glutamylcysteine |
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