title: Selenocysteine oxidation in glutathione peroxidase catalysis: an MS-supported quantum mechanics study.
abstract: Glutathione peroxidases (GPxs) are enzymes working with either selenium or sulfur catalysis. They adopted diverse functions ranging from detoxification of H(2)O(2) to redox signaling and differentiation. The relative stability of the selenoenzymes, however, remained enigmatic in view of the postulated involvement of a highly unstable selenenic acid form during catalysis. Nevertheless, density functional theory calculations obtained with a representative active site model verify the mechanistic concept of GPx catalysis and underscore its efficiency. However, they also allow that the selenenic acid, in the absence of the reducing substrate, reacts with a nitrogen in the active site. MS/MS analysis of oxidized rat GPx4 complies with the predicted structure, an 8-membered ring, in which selenium is bound as selenenylamide to the protein backbone. The intermediate can be re-integrated into the canonical GPx cycle by glutathione, whereas, under denaturing conditions, its selenium moiety undergoes β-cleavage with formation of a dehydro-alanine residue. The selenenylamide bypass prevents destruction of the redox center due to over-oxidation of the selenium or its elimination and likely allows fine-tuning of GPx activity or alternate substrate reactions for regulatory purposes.
authors.affiliation: Department of Chemistry, University of Padova, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Orian
authors.affiliation: Institute for Biomedical Technologies, National Research Council, Milano, Italy.
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Mauri
authors.affiliation: Department of Molecular Medicine, University of Padova, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Roveri
authors.affiliation: Department of Molecular Medicine, University of Padova, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Toppo
authors.affiliation: Institute for Biomedical Technologies, National Research Council, Milano, Italy.
authors.forename: Louise
authors.initials: L
authors.lastname: Benazzi
authors.affiliation: Department of Molecular Medicine, University of Padova, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Bosello-Travain
authors.affiliation: Institute for Biomedical Technologies, National Research Council, Milano, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: De Palma
authors.affiliation: Department of Molecular Medicine, University of Padova, Italy.
authors.forename: Matilde
authors.initials: M
authors.lastname: Maiorino
authors.affiliation: Department of Molecular Medicine, University of Padova, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Miotto
authors.affiliation: Department of Molecular Medicine, University of Padova, Italy.
authors.forename: Mattia
authors.initials: M
authors.lastname: Zaccarin
authors.affiliation: Department of Chemistry, University of Padova, Italy.
authors.forename: Antonino
authors.initials: A
authors.lastname: Polimeno
authors.affiliation: Department of Molecular Medicine, University of Padova, Italy. Electronic address: l.flohe@t-online.de.
authors.forename: Leopold
authors.initials: L
authors.lastname: Flohé
authors.affiliation: Department of Molecular Medicine, University of Padova, Italy.
authors.forename: Fulvio
authors.initials: F
authors.lastname: Ursini
mesh_terms: D000818:Animals; D002384:Catalysis; D005978:Glutathione / Q000737:chemistry* / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000737:chemistry* / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D011789:Quantum Theory; D051381:Rats; D012643:Selenium / Q000737:chemistry; D017279:Selenocysteine / Q000737:chemistry* / Q000378:metabolism; D013455:Sulfur / Q000737:chemistry; D053719:Tandem Mass Spectrometry
chemical_list: D017279:Selenocysteine; D013455:Sulfur; D006861:Hydrogen Peroxide; D005979:Glutathione Peroxidase; D005978:Glutathione; D012643:Selenium
keywords: DFT calculation; Glutathione peroxidases; MS/MS analysis of catalytic intermediates; Selenenylamide formation; Selenium catalysis