Tsuji Naoki, Nishikori Shingo, Iwabe Osamu, Shiraki Kentaro, Miyasaka Hitoshi, Takagi Masahiro, Hirata Kazumasa, Miyamoto Kazuhisa
Environmental Biotechnology Laboratory, Graduate School of Pharmaceutical Sciences, Osaka University, Suita, 1-6 Yamadaoka, Osaka 565-0871, Japan.
Biochem Biophys Res Commun. 2004 Mar 12;315(3):751-5. doi: 10.1016/j.bbrc.2004.01.122.
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.
植物螯合肽（PCs）作为高等植物、真核藻类、真菌和线虫中的重金属解毒肽而广为人知。相比之下，在任何原核生物中都从未鉴定出植物螯合肽或植物螯合肽合成酶基因。蓝藻念珠藻属Nostoc sp. PCC 7120的基因组序列最近已完成，这使我们能够鉴定出一个编码植物螯合肽合成酶样蛋白的基因，称为alr0975。alr0975的预测产物包含保守的N端结构域，但不包含真核植物螯合肽合成酶中发现的可变C端结构域。重组alr0975蛋白强烈催化植物螯合肽合成的第一步，即谷胱甘肽（GSH）转化为γ-谷氨酰半胱氨酸（γ-EC），尽管该蛋白仅微弱催化植物螯合肽合成的第二步，即将γ-EC部分转移至受体GSH分子以形成植物螯合肽（PC(2)）。这些结果表明，alr0975蛋白可能是真核生物中发现的植物螯合肽合成酶的一种更原始的形式。
