title: Cytochrome c peroxidase is a mitochondrial heme-based H2O2 sensor that modulates antioxidant defense.
abstract: Hydrogen peroxide (H2O2) is a key signaling molecule that also induces apoptosis. Thus, cells must rapidly sense and tightly control H2O2 levels. Well-characterized cellular responses to exogenous H2O2 involve oxidation of specific cytosolic protein-based thiols but sensing of H2O2 generated by mitochondrial respiration is less well described. Here we provide substantial biochemical evidence that the heme enzyme Ccp1 (cytochrome c peroxidase), which is targeted to the intermembrane space, functions primarily as a mitochondrial H2O2 sensing and signaling protein in Saccharomyces cerevisiae. Key evidence for a sensing role for Ccp1 is the significantly higher H2O2 accumulation in ccp1-null cells(ccp1Δ) vs ccp1(W191F) cells producing the catalytically inactive Ccp1(W191F) variant. In fact, intracellular H2O2 levels (ccp1Δ>wildtype >ccp1(W191F)) correlate inversely with the activity of the mitochondrial (and peroxisomal) heme catalase, Cta1 (ccp1Δ<wildtype <ccp1(W191F)). Mitochondrial Sod2 activity also varies in the three strains (ccp1Δ>wildtype >ccp1(W191F)) and ccp1Δ cells exhibit low superoxide levels. Notably, Ccp1(W191F) is a more persistent H2O2 signaling protein than wild-type Ccp1, and this enhanced mitochondrial H2O2 signaling decreases the mitochondrial fitness of ccp1(W191F) cells. However, these cells are fully protected from a bolus (0.4mM) of exogenous H2O2 added after 12h of growth, whereas the viability of ccp1Δ cells drops below 20%, which additionally associates Ccp1 with Yap1-dependent H2O2 signaling. Combined, our results strongly implicate Ccp1, independent of its peroxidase activity, in mitochondrial H2O2 sensing and signaling to maintain reactive oxygen species homeostasis.
authors.affiliation: PROTEO and Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, Canada, H4B 1R6.
authors.forename: Dorival
authors.initials: D
authors.lastname: Martins
authors.affiliation: PROTEO and Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, Canada, H4B 1R6.
authors.forename: Meena
authors.initials: M
authors.lastname: Kathiresan
authors.affiliation: PROTEO and Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, Canada, H4B 1R6. Electronic address: ann.english@concordia.ca.
authors.forename: Ann M
authors.initials: AM
authors.lastname: English
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D003578:Cytochrome-c Peroxidase / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D006418:Heme; D006861:Hydrogen Peroxide; D003578:Cytochrome-c Peroxidase
keywords: Antioxidant enzymes; Free radicals; H(2)O(2) sensing; H(2)O(2) signaling; Heme-based sensors; Mitochondrial ROS regulation