Intermediate Tyrosyl Radical and Amyloid Structure in Peroxide-Activated Cytoglobin

Abstract

We characterized the peroxidase mechanism of recombinant rat brain cytoglobin (Cygb) challenged by hydrogen peroxide, tert-butylhydroperoxide and by cumene hydroperoxide. The peroxidase mechanism of Cygb is similar to that of myoglobin. Cygb challenged by hydrogen peroxide is converted to a Fe4+ oxoferryl π cation, which is converted to Fe4+ oxoferryl and tyrosyl radical detected by direct continuous wave-electron paramagnetic resonance and by 3,5-dibromo-4-nitrosobenzene sulfonate spin trapping. When organic peroxides are used as substrates at initial reaction times, and given an excess of peroxide present, the EPR signals of the corresponding peroxyl radicals precede those of the direct tyrosyl radical. This result is consistent with the use of peroxide as a reducing agent for the recycling of Cygb high-valence species. Furthermore, we found that the Cygb oxidation by peroxides leads to the formation of amyloid fibrils. This result suggests that Cygb possibly participates in the development of degenerative diseases; our findings also support the possible biological role of Cygb related to peroxidase activity.

Cytoglobin protects cancer cells from apoptosis by regulation of mitochondrial cardiolipin

“…As well as DNA-crosslinking, cisplatin activity is known to involve mitochondrial ROS generation 29 , 30 , changes in mitochondrial membrane potential and damage to the electron transport chain triggering apoptosis and cell death 31 – 34 . Cytoglobin has been previously described as having peroxidase activity 14 , 21 , 35 , of which the local actions are uncertain within the overall context of the cellular redox state. Therefore, a better understanding of the mechanism by which cytoglobin protects cells from oxidative stress will result in novel targets for enhancing sensitivity and apoptosis signalling in cells to increase the effectiveness of cisplatin and other drugs in order to improve the outcome of existing treatments for cancers, including HNSCC.…”

Peroxidase Activity of Human Hemoproteins: Keeping the Fire under Control

“…NO binding to both heme-Fe(III) and heme-Fe(II) changes the optical absorbance spectra of hemeproteins in the Soret band region, but only Fe(II)-NO complexes have characteristic LT EPR spectra of nitrosylated heme ( Figure S2 ). The LT EPR method has been successfully employed for the study of pseudo-peroxidases and provided unique useful information [ 64 , 72 , 73 , 74 , 75 , 76 , 77 ].…”

“…The protein with disulfide bridge has a low temperature EPR signal at g ~ 6 [ 73 , 76 ]. The peroxidase mechanism of Cygb is similar to that of the pseudo-peroxidases discussed above.…”

“…The peroxidase mechanism of Cygb is similar to that of the pseudo-peroxidases discussed above. Interaction of the Cygb heme with H 2 O 2 results in formation of Fe(IV) oxoferryl π cation, which is converted to Fe(IV) oxoferryl and protein-derived (tyrosyl) radical detected by LT EPR and by spin trapping [ 76 ].…”

“…It oxidizes lipids five-fold faster than Mb. However, due to the low concentration of Cygb in cells and the protein degradation under strong oxidative conditions [ 76 ], Cygb-induced lipid oxidation is unlikely to cause extensive cellular damage [ 71 , 143 ]. The authors proposed that the physiological function of Cygb is to generate cell signaling lipid molecules under an oxidative environment.…”