InterPro domain: IPR007719

Phytochelatins are well known as the heavy metal-detoxifying peptides in higher plants, eukaryotic algae, fungi, nematode and cyanobacteria. Phytochelatin synthase (PCS, also known as glutathione gamma-glutamylcysteinyltransferase; 2.3.2.15 ) is involved in the synthesis of phytochelatins (PC) and homophytochelatins (hPC). This enzyme is required for detoxification of heavy metals such as cadmium and arsenate. The N-terminal region of phytochelatin synthase contains the active site, as well as four highly conserved cysteine residues that appear to play an important role in heavy-metal-induced phytochelatin catalysis. The C-terminal region is rich in cysteines, and may act as a metal sensor, whereby the Cys residues bind cadmium ions to bring them into closer proximity and transferring them to the activation site in the N-terminal catalytic domain [ 1 ]. The C-terminal region displays homology to the functional domains of metallothionein and metallochaperone.

This entry represents the N-terminal catalytic PCS domain, which belongs to the petidase family C83 of the papain superfamily of cysteine proteases, with a structurally conserved "catalytic triad" and oxyanion hole in the active site. It has an overall "crescent" shape with alpha/beta fold containing eight alpha-helices and six beta-strands [ 2 ].

1. Chelation of cadmium ions by phytochelatin synthase: role of the cysteine-rich C-terminal. null 24, 277-81
2. A papain-like enzyme at work: native and acyl-enzyme intermediate structures in phytochelatin synthesis. Proc. Natl. Acad. Sci. U.S.A. 102, 18848-53