PROSITE documentation PDOC51443

Phytochelatin synthase (PCS) domain profile

Phytochelatins (PCs) are well known as the heavy metal-detoxifying peptides in higher plants, eukaryotic algae, fungi, nematode and cyanobacteria. These peptides, of the general structure (γ-Glu-Cys)n-Gly (with n=2-11), are enzymatically synthesized from the substrate glutathione (GSH). PCs are synthesized posttranslationally by the PC synthase (PCS) (EC 2.3.2.15), a γ-glutamylcysteine (γ-EC) transpeptidase. PC synthesis is proposed to have two distinct steps: (Step1) formation of γ-EC concomitant with the cleavage of Gly from GSH; and (Step 2) transfer of the γ-EC unit to an acceptor GSH molecule or an oligomeric PC peptide (PCn). Eukaryotic PCS typically has a conserved N-terminal domain and a variable C-terminal domain, both of which are cysteine-rich. The N-terminal core domain is sufficient to confer a PCS activity and therefore can be referred to the catalytic domain. Cyanobacterial PCS contains the conserved N-terminal catalytic domain but not the variable C-terminal domain found in eukaryotic PCSs. It can act as a GSH hydrolase and weakly as a peptide ligase [1,2].

The catalytic PCS domain belongs to the petidase family C83 of the papain superfamily of cysteine proteases [E1], with the structurally conserved "catalytic triad" and oxyanion hole in the active site. It has an overall "crescent" shape with α/β fold containing eight α-helices and six β-strands (see <PDB:2BTW>) [2].

The profile we developed covers the entire PCS domain.