Abstract

Phytochelatin synthase (PCS) is well-known for its role in heavy metal detoxification in plants, yeasts and non-vertebrate animals. It is a protease-like enzyme that catalyzes glutathione (GSH) to form phytochelatins (PCs), a group of Cys-rich and non-translational polypeptides with a high affinity to heavy metals. In addition, PCS also functions in xenobiotic metabolism by processing GS-conjugates in the cytosol. Because PCS is involved in GSH metabolism and the degradation of GS-conjugates, it is one of the important components in GSH homeostasis and GSH-mediated biodegradation. This chapter reviews the biochemical mechanism of PCS, how the enzyme activity is regulated, and its roles in heavy metal detoxification as well as GS-S-conjugate metabolism. This chapter also highlights the potential applications of PCS in the improvement of plant performance under combined stresses.

Highlights

  • Phytochelatins (PCs,n-Gly, n = 2–11) are cysteine-rich polypeptides that are synthesized non-translationally from the tripeptide glutathione (GSH, γGlu-CysGly); this process is catalyzed by phytochelatin synthase (PCS, EC 2.3.2.15) [1–4]

  • This chapter summarizes the critical role of Phytochelatin synthase (PCS) in heavy metal detoxification and the involvement of PCS in GS-conjugate degradation

  • In the presence of heavy metals, PCS catalyzes the synthesis of PCs and the initiation of GS-conjugate metabolism

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Summary

Introduction

PCS can be found in plants, yeasts and non-vertebrate animals and plays a critical role in responding to heavy metal stress in these organisms [28–32]. It was first partially purified from the suspension cells of bladder campion (Silene cucubalus) for its ability to synthesize PCs from GSH in the presence of Cd2+ [4]. The catalytic-site mutants of PCS are still functional in this pathway, which suggests that the role of PCS in the indole glucosinolate metabolism is independent of PC synthesis and GS-metabolism [51] Among these PCSinvolving biological processes, this chapter focuses on the catalytic mechanism of PCS and its functions in both heavy metal stress and GSH metabolism. The potential applications of PCS in combating multiple stresses are discussed

The domain organization of phytochelatin synthase
The core catalytic mechanism
Critical amino acids contributing to the enzyme activity
The activation of phytochelatin synthase through the chelation of heavy metal ions
The effects of phytochelatin synthase overexpression on the accumulation of heavy metals in plants
Phytochelatin synthase-involving pathway engineering for enhancing heavy metal accumulation
The involvement of phytochelatin synthase in the catabolism of glutathione derivates
The glutathione-S-conjugate conversion via phytochelatin synthase is metal-dependent
Findings
Conclusion
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