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Gene Review

PCS1  -  aspartic proteinase PCS1

Arabidopsis thaliana

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Disease relevance of PCS1

  • To clarify the mechanism of PC synthase found in eukaryotes, we have compared the two-step reactions catalyzed by the prokaryotic Nostoc PC synthase (NsPCS) and the eukaryotic Arabidopsis PC synthase (AtPCS1) [1].
  • The overexpressed AtPCS1 protein itself was not responsible for Cd hypersensitivity as transgenic cad1-3 mutants overexpressing AtPCS1 to similar levels as those of pcs lines were not hypersensitive to Cd [2].
  • Even when AtPCS2 was under the control of the AtPCS1 promoter or of the cauliflower mosaic virus 35S promoter (CaMV 35S) it was not capable of fully complementing the cad1-3 mutant for cadmium resistance [3].

High impact information on PCS1

  • 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 [4].
  • As revealed by the results of in vivo and in vitro functional assays, the core PCS_Nt2 fragment is biosynthetically active in the presence of cadmium ions and supports phytochelatin formation at a rate that is only approximately 5-fold lower than that of full-length AtPCS1 [5].
  • As exemplified by Cd(2+)- and Zn(2+)-dependent AtPCS1-mediated catalysis, the kinetics of PC synthesis approximate a substituted enzyme mechanism in which micromolar heavy metal glutathione thiolate (e.g. Cd.GS(2) or Zn.GS(2)) and free glutathione act as gamma-Glu-Cys acceptor and donor [6].
  • PCS1 provides a new avenue for understanding the mechanisms of the programmed cell death processes that are associated with developmental pathways in plants and makes available a useful tool for engineering the male sterility trait for hybrid seed production [7].
  • We have found that the PROMOTION OF CELL SURVIVAL 1 (PCS1) gene in Arabidopsis, which encodes an aspartic protease, has an important role in determining the fate of cells in embryonic development and in reproduction processes [7].

Biological context of PCS1

  • The loss-of-function mutation of PCS1 causes degeneration of both male and female gametophytes and excessive cell death of developing embryos [7].
  • Furthermore, functional analyses of various mutants of NsPCS and AtPCS1, selected by comparing the sequences of NsPCS and AtPCS1, indicate that the N-terminal region (residues 1-221) in AtPCS1 is the catalytic domain, and in this region, the Cys(56) residue is associated with the PC synthesis reaction [1].
  • Further, as demonstrated by the facility of AtPCS1 for the net synthesis of S-alkyl-PCs from S-alkylglutathiones with biphasic kinetics, consistent with the sufficiency of S-alkylglutathiones as both gamma-Glu-Cys donors and acceptors in media devoid of metals, even heavy metal thiolates are dispensable [6].

Associations of PCS1 with chemical compounds

  • Cd(2+) tolerance in cultured rolB roots was increased as a result of overexpression of AtPCS1, and further enhanced when reduced glutathione (GSH, the substrate of PCS1) was added to the culture medium [8].
  • We conclude that the increase in Cd(2+) tolerance and accumulation of PCS1 overexpressing plants is directly related to the availability of GSH, while overexpression of phytochelatin synthase does not enhance long distance root-to-shoot Cd(2+) transport [8].
  • A purified N-terminally hexahistidinyl-tagged AtPCS1 truncate containing only the first 221 N-terminal amino acid residues of the enzyme (HIS-AtPCS1_221tr) is competent in the synthesis of PCs from GSH in media containing Cd2+ or the synthesis of S-methyl-PCs from S-methylglutathione in media devoid of heavy metal ions [9].
  • Recombinant LjPCS1 and Arabidopsis (Arabidopsis thaliana) PCS1 (AtPCS1) were affinity purified and their polyhistidine-tags removed [10].
  • Through the application of sequence search algorithms capable of detecting distant homologies, work we reported briefly before but not in its entirety, it has been determined that the N-terminal half of AtPCS1 and its equivalents from other sources have the hallmarks of a papain-like, Clan CA Cys protease [9].

Other interactions of PCS1


Analytical, diagnostic and therapeutic context of PCS1

  • Accordingly, HPLC analysis showed that total PC production in PCS1-overexpressing rolB roots was higher than in rolB roots in the presence of GSH [8].
  • This shortfall in our basic understanding of AtPCS1 is addressed here by the results of systematic site-directed mutagenesis studies that demonstrate that not only Cys-56 but also His-162 and Asp-180 are indeed required for net PC synthesis [9].
  • Northern and Western blot analyses showed that expression of AtPCS2 is weak compared to AtPCS1 in both roots and shoots of transgenic Arabidopsis [3].


  1. Comparative analysis of the two-step reaction catalyzed by prokaryotic and eukaryotic phytochelatin synthase by an ion-pair liquid chromatography assay. Tsuji, N., Nishikori, S., Iwabe, O., Matsumoto, S., Shiraki, K., Miyasaka, H., Takagi, M., Miyamoto, K., Hirata, K. Planta (2005) [Pubmed]
  2. Overexpression of Arabidopsis phytochelatin synthase paradoxically leads to hypersensitivity to cadmium stress. Lee, S., Moon, J.S., Ko, T.S., Petros, D., Goldsbrough, P.B., Korban, S.S. Plant Physiol. (2003) [Pubmed]
  3. Expression of Arabidopsis phytochelatin synthase 2 is too low to complement an AtPCS1-defective Cad1-3 mutant. Lee, S., Kang, B.S. Mol. Cells (2005) [Pubmed]
  4. AtPCS1, a phytochelatin synthase from Arabidopsis: isolation and in vitro reconstitution. Vatamaniuk, O.K., Mari, S., Lu, Y.P., Rea, P.A. Proc. Natl. Acad. Sci. U.S.A. (1999) [Pubmed]
  5. Domain organization of phytochelatin synthase: functional properties of truncated enzyme species identified by limited proteolysis. Ruotolo, R., Peracchi, A., Bolchi, A., Infusini, G., Amoresano, A., Ottonello, S. J. Biol. Chem. (2004) [Pubmed]
  6. Mechanism of heavy metal ion activation of phytochelatin (PC) synthase: blocked thiols are sufficient for PC synthase-catalyzed transpeptidation of glutathione and related thiol peptides. Vatamaniuk, O.K., Mari, S., Lu, Y.P., Rea, P.A. J. Biol. Chem. (2000) [Pubmed]
  7. An Arabidopsis aspartic protease functions as an anti-cell-death component in reproduction and embryogenesis. Ge, X., Dietrich, C., Matsuno, M., Li, G., Berg, H., Xia, Y. EMBO Rep. (2005) [Pubmed]
  8. Overexpression of Arabidopsis phytochelatin synthase in tobacco plants enhances Cd(2+) tolerance and accumulation but not translocation to the shoot. Pomponi, M., Censi, V., Di Girolamo, V., De Paolis, A., di Toppi, L.S., Aromolo, R., Costantino, P., Cardarelli, M. Planta (2006) [Pubmed]
  9. Mutagenic definition of a papain-like catalytic triad, sufficiency of the N-terminal domain for single-site core catalytic enzyme acylation, and C-terminal domain for augmentative metal activation of a eukaryotic phytochelatin synthase. Romanyuk, N.D., Rigden, D.J., Vatamaniuk, O.K., Lang, A., Cahoon, R.E., Jez, J.M., Rea, P.A. Plant Physiol. (2006) [Pubmed]
  10. A reassessment of substrate specificity and activation of phytochelatin synthases from model plants by physiologically relevant metals. Loscos, J., Naya, L., Ramos, J., Clemente, M.R., Matamoros, M.A., Becana, M. Plant Physiol. (2006) [Pubmed]
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