Family C83


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family C83

Family type peptidaseC83.001 - gamma-glutamylcysteine dipeptidyltranspeptidase (Nostoc sp. PCC 7120), MEROPS Accession MER0081295 (peptidase unit: 1-242)
Content of familyThe family contains exopeptidases some of which also have transferase activity.
History Identifier created: MEROPS 8.0 (8 January 2008)
The synthesis of phytochelatins by the action of a gamma-glutamylcysteine dipeptidyl transpeptidase was described by Grill et al., 1989. Phytochelatins are the principle heavy-metal detoxifying compounds in the plant kingdom. They are linear polymers of the gamma-Glu-Cys portion of glutathione (GSH), with the general formula (Glu-Cys)n-Gly, where n= 2-11. In the related iso-phytochelatins the C-terminal Gly is replaced by Ser, Glu or Gln, and in homo-phytochelatin it is beta-Ala (Oven et al., 2002). The family also contains enzymes that hydrolyse the terminal Gly from glutathione (gamma-Glu-Cys-Gly) but lack the transferase activity necessary for the synthesis of phytochelatin. Glutathione is gamma-Glu-Cys-Gly, and its degradation by cleavage of the C-terminal Gly contrasts with the action of the gamma-glutamyltransfereses (e.g. T03.001) that remove the N-terminal residue.
Catalytic typeCysteine
Active site residuesQ64 C70 H183 D201 
Active siteThe active site is similar to that of papain, containing Gln, Cys, His and Asp (see the Alignment).
Activities and specificitiesGlutathione is cleaved to gamma-Glu-Cys + Gly, either by hydrolysis or transpeptidation. The subset of enzymes in the family that catalyse the transpeptidation reaction produce phytochelatin, and are termed phytochelatin synthases. The formation of phytochelatin is stimulated by heavy metal ions.
Molecular structureThe papain-like crystal structure of the gamma-glutamylcysteine dipeptidyl transpeptidase NsPCS from Nostoc places family C83 in clan CA (Vivares et al., 2005).
Distribution of family Bacteria details  
Archaea -  
Protozoa details  
Fungi details  
Plants details  
Animals details  
Viruses -  
Biological functionsThe formation of phytochelatin is important because ions of heavy metals such as mercury and cadmium are tightly complexed by phytochelatin and are thus rendered harmless. The AtPCS1 phytochelatin synthase of Arabidopsis also plays a role in the degradation of glutathione conjugates (Blum et al., 2007).
Pharmaceutical and biotech relevanceIt is possible that some organisms can be made more resistant to environmental toxins by enhanced actvity of phytochelatin synthase (Gasic & Korban, 2007; Konishi et al. 2006).
ReviewsRea (2006)
Statistics for family C83Sequences:633
Identifiers with PDB entries:1
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
gamma-glutamylcysteine dipeptidyltranspeptidaseC83.001Yes
phytochelatin synthaseC83.002-
phytochelatin synthase (Caenorhabditis-type)C83.003-
phytochelatin synthase 2C83.004-
DDB_G0291187 protein (Dictyostelium discoideum)C83.A02-
family C83 non-peptidase homologuesnon-peptidase homologue-
family C83 unassigned peptidasesunassigned-