Vatamaniuk O K, Mari S, Lu Y P, Rea P A
Plant Science Institute, Department of Biology, University of Pennsylvania, Philadelphia, PA 19104, USA.
Proc Natl Acad Sci U S A. 1999 Jun 8;96(12):7110-5. doi: 10.1073/pnas.96.12.7110.
Phytochelatins, a class of posttranslationally synthesized peptides, play a pivotal role in heavy metal, primarily Cd2+, tolerance in plants and fungi by chelating these substances and decreasing their free concentrations. Derived from glutathione and related thiols by the action of gamma-glutamylcysteine dipeptidyl transpeptidases (phytochelatin synthases; EC 2.3.2.15), phytochelatins consist of repeating units of gamma-glutamylcysteine followed by a C-terminal Gly, Ser, or beta-Ala residue [poly-(gamma-Glu-Cys)n-Xaa]. Here we report the suppression cloning of a cDNA (AtPCS1) from Arabidopsis thaliana encoding a 55-kDa soluble protein that enhances heavy-metal tolerance and elicits Cd2+-activated phytochelatin accumulation when expressed in Saccharomyces cerevisiae. On the basis of these properties and the sufficiency of immunoaffinity-purified epitope-tagged AtPCS1 polypeptide for high rates of Cd2+-activated phytochelatin synthesis from glutathione in vitro, AtPCS1 is concluded to encode the enzyme phytochelatin synthase.
植物螯合肽是一类翻译后合成的肽,通过螯合重金属(主要是Cd2+)并降低其游离浓度,在植物和真菌对重金属的耐受性方面发挥关键作用。植物螯合肽由γ-谷氨酰半胱氨酸二肽基转肽酶(植物螯合肽合成酶;EC 2.3.2.15)作用于谷胱甘肽和相关硫醇衍生而来,由γ-谷氨酰半胱氨酸的重复单元组成,随后是C末端的甘氨酸、丝氨酸或β-丙氨酸残基[聚(γ-Glu-Cys)n-Xaa]。在此,我们报告了从拟南芥中克隆出一个cDNA(AtPCS1),它编码一种55 kDa的可溶性蛋白,该蛋白在酿酒酵母中表达时可增强重金属耐受性并引发Cd2+激活的植物螯合肽积累。基于这些特性以及免疫亲和纯化的表位标记AtPCS1多肽在体外能以高比率从谷胱甘肽合成Cd2+激活的植物螯合肽的充分性,得出AtPCS1编码植物螯合肽合成酶的结论。