A papain-like enzyme at work: native and acyl-enzyme intermediate structures in phytochelatin synthesis.
Phytochelatin synthase (PCS) is a key enzyme for heavy-metal detoxification in plants. PCS catalyzes the production of glutathione (GSH)-derived peptides (called phytochelatins or PCs) that bind heavy-metal ions before vacuolar sequestration. The enzyme can also hydrolyze GSH and GS-conjugated xenobiotics. In the cyanobacterium Nostoc, the enzyme (NsPCS) contains only the catalytic domain of the eukaryotic synthase and can act as a GSH hydrolase and weakly as a peptide ligase. The crystal structure of NsPCS in its native form solved at a 2.0-A resolution shows that NsPCS is a dimer that belongs to the papain superfamily of cysteine proteases, with a conserved catalytic machinery. Moreover, the structure of the protein solved as a complex with GSH at a 1.4-A resolution reveals a gamma-glutamyl cysteine acyl-enzyme intermediate stabilized in a cavity of the protein adjacent to a second putative GSH binding site. GSH hydrolase and PCS activities of the enzyme are discussed in the light of both structures.
Vivares
Denis
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Département d'Ecophysiologie Végétale et de Microbiologie, Direction des Sciences du Vivant, Laboratoire de Bioénergétique Cellulaire, Commissariat á l'Energie Atomique/Cadarache, 13108 St Paul lez Durance Cedex, France.
Arnoux
Pascal
P
Pignol
David
D
D000595:Amino Acid Sequence; D019881:Aminoacyltransferases / Q000737:chemistry; D000838:Anions; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D005978:Glutathione / Q000737:chemistry*; D005982:Glutathione Transferase / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046937:Nostoc / Q000378:metabolism; D010206:Papain / Q000737:chemistry*; D054811:Phytochelatins; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012984:Software; D013696:Temperature; D013997:Time Factors; D015262:Xenobiotics / Q000737:chemistry
D000838:Anions; D015262:Xenobiotics; D054811:Phytochelatins; D019881:Aminoacyltransferases; C093784:glutathione gamma-glutamylcysteinyltransferase; D005982:Glutathione Transferase; D010206:Papain; D005978:Glutathione; D003545:Cysteine