6THO

Acylintermediate of glutathione and the mature primitive phytochelatin synthase Alr0975 from Nostoc PCC 7120 at atomic resolution.

Summary for 6THO

• Entry DOI: 10.2210/pdb6tho/pdb
• Descriptor: Alr0975 protein, OXIDIZED GLUTATHIONE DISULFIDE, CALCIUM ION, ... (4 entities in total)
• Functional Keywords: glutathione, phytochelatin, detoxification, chelating heavy atoms, transferase
• Biological source: Nostoc sp. PCC 7120
• Total number of polymer chains: 2
• Total formula weight: 51520.37

Authors

Feiler, C.G.,Blankenfeldt, W. (deposition date: 2019-11-20, release date: 2020-12-02, Last modification date: 2025-10-01)

Primary citation

Gisdon, F.J.,Feiler, C.G.,Kempf, O.,Foerster, J.M.,Haiss, J.,Blankenfeldt, W.,Ullmann, G.M.,Bombarda, E.
Structural and Biophysical Analysis of the Phytochelatin-Synthase-Like Enzyme from Nostoc sp. Shows That Its Protease Activity is Sensitive to the Redox State of the Substrate.
Acs Chem.Biol., 17:883-897, 2022

PubMed Abstract: Phytochelatins (PCs) are nonribosomal thiol-rich oligopeptides synthetized from glutathione (GSH) in a γ-glutamylcysteinyl transpeptidation reaction catalyzed by PC synthases (PCSs). Ubiquitous in plant and present in some invertebrates, PCSs are involved in metal detoxification and homeostasis. The PCS-like enzyme from the cyanobacterium sp. (NsPCS) is considered to be an evolutionary precursor enzyme of genuine PCSs because it shows sufficient sequence similarity for homology to the catalytic domain of the eukaryotic PCSs and shares the peptidase activity consisting in the deglycination of GSH. In this work, we investigate the catalytic mechanism of NsPCS by combining structural, spectroscopic, thermodynamic, and theoretical techniques. We report several crystal structures of NsPCS capturing different states of the catalyzed chemical reaction: (i) the structure of the wild-type enzyme (wt-NsPCS); (ii) the high-resolution structure of the γ-glutamyl-cysteine acyl-enzyme intermediate (acyl-NsPCS); and (iii) the structure of an inactive variant of NsPCS, with the catalytic cysteine mutated into serine (C70S-NsPCS). We characterize NsPCS as a relatively slow enzyme whose activity is sensitive to the redox state of the substrate. Namely, NsPCS is active with reduced glutathione (GSH), but is inhibited by oxidized glutathione (GSSG) because the cleavage product is not released from the enzyme. Our biophysical analysis led us to suggest that the biological function of NsPCS is being a part of a redox sensing system. In addition, we propose a mechanism how PCS-like enzymes may have evolved toward genuine PCS enzymes.

PubMed: 35377603
DOI: 10.1021/acschembio.1c00941

Experimental method

X-RAY DIFFRACTION (1.09 Å)