Weeds, Worms, and More. Papain's Long-Lost Cousin, Phytochelatin Synthase

This Update is concerned with the mechanism of synthesis of heavy metal-binding thiol peptides, phytochelatins (PCs), by the enzyme PC synthase (EC 2.3.2.15). The bulk of the considerations in this review centers on what has been learned recently of the fundamental mechanics of PC synthesis, the domain organization and phylogenetic distribution of PC synthases, and PC synthase-like enzymes, and what this tells us about the chemistry underlying and the enzyme residues necessary for PC synthesis. It was decided to prepare a review of this type rather than aim at a more comprehensive treatment of heavy metal homeostasis and detoxification in plants for two reasons. The first is that there are already several contemporary reviews dealing with the more global aspects of plant heavy metal physiology. Excellent examples are Cobbett (2000), Clemens (2001), and Cobbett and Goldsbrough (2002). Readers who have not already read these are encouraged to do so. The second reason is that some of the most fascinating and unexpected developments for our understanding in this area of late derive from investigations of the catalytic mechanism and distribution of PC synthases, facets of this field of research that have yet to be reviewed in detail.