Limits...
Destroy and exploit: catalyzed removal of hydroperoxides from the endoplasmic reticulum.

Ramming T, Appenzeller-Herzog C - Int J Cell Biol (2013)

Bottom Line: Peroxidases are enzymes that reduce hydroperoxide substrates.Different peroxide sources and reducing substrates for ER peroxidases are critically evaluated.Peroxidase-catalyzed detoxification of hydroperoxides coupled to the productive use of disulfides, for instance, in the ER-associated process of oxidative protein folding, appears to emerge as a common theme.

View Article: PubMed Central - PubMed

Affiliation: Division of Molecular and Systems Toxicology, Department of Pharmaceutical Sciences, University of Basel, Klingelbergstr. 50, 4056 Basel, Switzerland.

ABSTRACT
Peroxidases are enzymes that reduce hydroperoxide substrates. In many cases, hydroperoxide reduction is coupled to the formation of a disulfide bond, which is transferred onto specific acceptor molecules, the so-called reducing substrates. As such, peroxidases control the spatiotemporal distribution of diffusible second messengers such as hydrogen peroxide (H2O2) and generate new disulfides. Members of two families of peroxidases, peroxiredoxins (Prxs) and glutathione peroxidases (GPxs), reside in different subcellular compartments or are secreted from cells. This review discusses the properties and physiological roles of PrxIV, GPx7, and GPx8 in the endoplasmic reticulum (ER) of higher eukaryotic cells where H2O2 and-possibly-lipid hydroperoxides are regularly produced. Different peroxide sources and reducing substrates for ER peroxidases are critically evaluated. Peroxidase-catalyzed detoxification of hydroperoxides coupled to the productive use of disulfides, for instance, in the ER-associated process of oxidative protein folding, appears to emerge as a common theme. Nonetheless, in vitro and in vivo studies have demonstrated that individual peroxidases serve specific, nonoverlapping roles in ER physiology.

No MeSH data available.


Related in: MedlinePlus

Suggested reaction mechanisms of GPx7. (a) Following peroxide-mediated oxidation of the active site Cys (C57), sulfenylated C57 is either directly subjected to nucleophilic attack by a (deprotonated) Cys in the reducing substrate (PDIs/GRP78) or attacked by (deprotonated) Cys86, which results in formation of an intramolecular disulfide bond. In a second step, this intramolecular disulfide is attacked by a Cys in the reducing substrate. Both pathways converge in the formation of an intermolecular disulfide-bonded intermediate between GPx7 and the reducing substrate prior to the completion of the reaction cycle, which gives rise to regenerated, reduced GPx7 and oxidized PDIs/GRP78. (b) Hypothesized conformational change prior to formation of a Cys57–Cys86 disulfide bond in GPx7 is depicted on the structure of reduced GPx7 (PDB ID 2KIJ). Active site rearrangement upon oxidation of Cys57 might involve a stacking interaction between the conserved aromatic side chains of Phe89 and Trp142 (green), which would move away Trp142 from Cys57 (dashed white arrow).
© Copyright Policy - open-access
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3824332&req=5

fig4: Suggested reaction mechanisms of GPx7. (a) Following peroxide-mediated oxidation of the active site Cys (C57), sulfenylated C57 is either directly subjected to nucleophilic attack by a (deprotonated) Cys in the reducing substrate (PDIs/GRP78) or attacked by (deprotonated) Cys86, which results in formation of an intramolecular disulfide bond. In a second step, this intramolecular disulfide is attacked by a Cys in the reducing substrate. Both pathways converge in the formation of an intermolecular disulfide-bonded intermediate between GPx7 and the reducing substrate prior to the completion of the reaction cycle, which gives rise to regenerated, reduced GPx7 and oxidized PDIs/GRP78. (b) Hypothesized conformational change prior to formation of a Cys57–Cys86 disulfide bond in GPx7 is depicted on the structure of reduced GPx7 (PDB ID 2KIJ). Active site rearrangement upon oxidation of Cys57 might involve a stacking interaction between the conserved aromatic side chains of Phe89 and Trp142 (green), which would move away Trp142 from Cys57 (dashed white arrow).

Mentions: Irrespective of the peroxide source, the catalytic mechanism for the reductive regeneration of GPx7/8 remains controversial. Despite the absence of a canonical CR, GPx7 and 8 harbor an additional cysteine in a conserved Pro-Cys86/108-Asn-Gln-Phe motif [86]. Studies with GPx7 have highlighted two possible mechanisms of peroxidase reduction [86, 89, 90] (Figure 4(a)). Of note, one of the possibilities features Cys86 as a noncanonical CR. However, since CP and Cys86 are ~11 Å apart in the crystal structure (Figure 4(b)), this implies a major conformational change. Indeed upon H2O2 addition, the intrinsic fluorescence of Trp142, which, in reduced GPx7, is particularly solvent-exposed and in close proximity to CP (Figure 4(b)), readily resumes in the time scale of 2-3 sec after initial decline [88, 89]. This likely indicates the translocation of Trp142 away from the fluorescence-quenching CP sulfenic acid. In this connection, we note the adjacent aromatic side chain of Phe89, which is part of the conserved motif surrounding Cys86 (see above), and speculate that stacking of Phe89 and Trp142 upon CP oxidation could promote formation of the CP–Cys86 disulfide (Figure 4(b)). Interestingly, in addition to the Pro-Cys-Asn-Gln-Phe motif, the exposed Trp residue is conserved throughout the GPx family [86].


Destroy and exploit: catalyzed removal of hydroperoxides from the endoplasmic reticulum.

Ramming T, Appenzeller-Herzog C - Int J Cell Biol (2013)

Suggested reaction mechanisms of GPx7. (a) Following peroxide-mediated oxidation of the active site Cys (C57), sulfenylated C57 is either directly subjected to nucleophilic attack by a (deprotonated) Cys in the reducing substrate (PDIs/GRP78) or attacked by (deprotonated) Cys86, which results in formation of an intramolecular disulfide bond. In a second step, this intramolecular disulfide is attacked by a Cys in the reducing substrate. Both pathways converge in the formation of an intermolecular disulfide-bonded intermediate between GPx7 and the reducing substrate prior to the completion of the reaction cycle, which gives rise to regenerated, reduced GPx7 and oxidized PDIs/GRP78. (b) Hypothesized conformational change prior to formation of a Cys57–Cys86 disulfide bond in GPx7 is depicted on the structure of reduced GPx7 (PDB ID 2KIJ). Active site rearrangement upon oxidation of Cys57 might involve a stacking interaction between the conserved aromatic side chains of Phe89 and Trp142 (green), which would move away Trp142 from Cys57 (dashed white arrow).
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3824332&req=5

fig4: Suggested reaction mechanisms of GPx7. (a) Following peroxide-mediated oxidation of the active site Cys (C57), sulfenylated C57 is either directly subjected to nucleophilic attack by a (deprotonated) Cys in the reducing substrate (PDIs/GRP78) or attacked by (deprotonated) Cys86, which results in formation of an intramolecular disulfide bond. In a second step, this intramolecular disulfide is attacked by a Cys in the reducing substrate. Both pathways converge in the formation of an intermolecular disulfide-bonded intermediate between GPx7 and the reducing substrate prior to the completion of the reaction cycle, which gives rise to regenerated, reduced GPx7 and oxidized PDIs/GRP78. (b) Hypothesized conformational change prior to formation of a Cys57–Cys86 disulfide bond in GPx7 is depicted on the structure of reduced GPx7 (PDB ID 2KIJ). Active site rearrangement upon oxidation of Cys57 might involve a stacking interaction between the conserved aromatic side chains of Phe89 and Trp142 (green), which would move away Trp142 from Cys57 (dashed white arrow).
Mentions: Irrespective of the peroxide source, the catalytic mechanism for the reductive regeneration of GPx7/8 remains controversial. Despite the absence of a canonical CR, GPx7 and 8 harbor an additional cysteine in a conserved Pro-Cys86/108-Asn-Gln-Phe motif [86]. Studies with GPx7 have highlighted two possible mechanisms of peroxidase reduction [86, 89, 90] (Figure 4(a)). Of note, one of the possibilities features Cys86 as a noncanonical CR. However, since CP and Cys86 are ~11 Å apart in the crystal structure (Figure 4(b)), this implies a major conformational change. Indeed upon H2O2 addition, the intrinsic fluorescence of Trp142, which, in reduced GPx7, is particularly solvent-exposed and in close proximity to CP (Figure 4(b)), readily resumes in the time scale of 2-3 sec after initial decline [88, 89]. This likely indicates the translocation of Trp142 away from the fluorescence-quenching CP sulfenic acid. In this connection, we note the adjacent aromatic side chain of Phe89, which is part of the conserved motif surrounding Cys86 (see above), and speculate that stacking of Phe89 and Trp142 upon CP oxidation could promote formation of the CP–Cys86 disulfide (Figure 4(b)). Interestingly, in addition to the Pro-Cys-Asn-Gln-Phe motif, the exposed Trp residue is conserved throughout the GPx family [86].

Bottom Line: Peroxidases are enzymes that reduce hydroperoxide substrates.Different peroxide sources and reducing substrates for ER peroxidases are critically evaluated.Peroxidase-catalyzed detoxification of hydroperoxides coupled to the productive use of disulfides, for instance, in the ER-associated process of oxidative protein folding, appears to emerge as a common theme.

View Article: PubMed Central - PubMed

Affiliation: Division of Molecular and Systems Toxicology, Department of Pharmaceutical Sciences, University of Basel, Klingelbergstr. 50, 4056 Basel, Switzerland.

ABSTRACT
Peroxidases are enzymes that reduce hydroperoxide substrates. In many cases, hydroperoxide reduction is coupled to the formation of a disulfide bond, which is transferred onto specific acceptor molecules, the so-called reducing substrates. As such, peroxidases control the spatiotemporal distribution of diffusible second messengers such as hydrogen peroxide (H2O2) and generate new disulfides. Members of two families of peroxidases, peroxiredoxins (Prxs) and glutathione peroxidases (GPxs), reside in different subcellular compartments or are secreted from cells. This review discusses the properties and physiological roles of PrxIV, GPx7, and GPx8 in the endoplasmic reticulum (ER) of higher eukaryotic cells where H2O2 and-possibly-lipid hydroperoxides are regularly produced. Different peroxide sources and reducing substrates for ER peroxidases are critically evaluated. Peroxidase-catalyzed detoxification of hydroperoxides coupled to the productive use of disulfides, for instance, in the ER-associated process of oxidative protein folding, appears to emerge as a common theme. Nonetheless, in vitro and in vivo studies have demonstrated that individual peroxidases serve specific, nonoverlapping roles in ER physiology.

No MeSH data available.


Related in: MedlinePlus