Vivares Denis, Arnoux Pascal, Pignol David
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.
Proc Natl Acad Sci U S A. 2005 Dec 27;102(52):18848-53. doi: 10.1073/pnas.0505833102. Epub 2005 Dec 9.
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.
植物螯合肽合成酶（PCS）是植物中重金属解毒的关键酶。PCS催化产生谷胱甘肽（GSH）衍生的肽（称为植物螯合肽或PCs），这些肽在液泡隔离之前结合重金属离子。该酶还可以水解GSH和GS共轭的异生物质。在蓝细菌念珠藻中，该酶（NsPCS）仅包含真核合成酶的催化结构域，并且可以作为GSH水解酶起作用，而作为肽连接酶的作用较弱。以2.0埃分辨率解析的天然形式的NsPCS晶体结构表明，NsPCS是一种二聚体，属于半胱氨酸蛋白酶的木瓜蛋白酶超家族，具有保守的催化机制。此外，以1.4埃分辨率解析的与GSH形成复合物的蛋白质结构揭示了一种γ-谷氨酰半胱氨酸酰基酶中间体，该中间体稳定在蛋白质的一个腔中，该腔与第二个假定的GSH结合位点相邻。根据这两种结构讨论了该酶的GSH水解酶和PCS活性。
