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DNA cleavage mediated by copper superoxide dismutase via two pathways
Yingchun Han1, Tao Shen, Wei Jiang
1Department of Chemistry, Huazhong University of Science and Technology, Wuhan 430074, China.
Journal of Inorganic Biochemistry
|October 31, 2006
Summary
Copper, zinc superoxide dismutase (Cu(2)Zn(2)SOD) can damage DNA. This study shows Cu(n)SOD, with varying copper ions, mediates DNA cleavage via oxidative and hydrolytic pathways, independent of copper ion number.
Area of Science:
- Biochemistry
- Molecular Biology
- Oxidative Stress Research
Background:
- Copper, zinc superoxide dismutase (Cu(2)Zn(2)SOD) is vital for cellular protection against oxidative stress by converting superoxide radicals.
- However, excessive Cu(2)Zn(2)SOD can be detrimental, indicating complex roles beyond simple protection.
- The aberrant copper-mediated chemistry in Cu(2)Zn(2)SOD, particularly its DNA cleavage potential, remains incompletely understood.
Purpose of the Study:
- To investigate the DNA cleavage activity of copper-containing superoxide dismutase (Cu(n)SOD) with varying copper ion content.
- To elucidate the mechanisms underlying copper-mediated oxidative chemistry within Cu(n)SOD.
- To determine the role of copper ions and the protein structure in the DNA cleavage activity of Cu(n)SOD.
Main Methods:
- Metallation of apo-Cu(2)Zn(2)SOD with varying concentrations of Cu(II) to create Cu(n)SOD variants.
- Assay of SOD activity and DNA cleavage using supercoiled DNA as a substrate in the presence of hydrogen peroxide or mercaptoethanol.
- Kinetic studies and investigation of the effects of EDTA, radical scavengers, bicarbonate, and carbon dioxide on DNA cleavage.
Main Results:
- Cu(n)SOD exhibited significant DNA cleavage activity, which was dependent on the presence of hydrogen peroxide or mercaptoethanol.
- This DNA cleavage activity was specific to certain proteins, including Cu(n)SOD, and distinct from free Cu(II) ions.
- The activity was independent of the number of copper ions in Cu(n)SOD, suggesting a cooperative interaction between the protein and copper.
Conclusions:
- DNA cleavage by Cu(n)SOD occurs through both hydroxyl radical oxidation and hydroxide ion hydrolysis pathways.
- The study implies that all copper-containing SOD enzymes, including Cu(2)Zn(2)SOD and its mutants, possess DNA cleavage potential.
- These findings highlight a potential cytotoxic mechanism of SOD enzymes under specific conditions, contributing to understanding oxidative stress.
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