Radical-induced damage to proteins: e.s.r. spin-trapping studies

Area of Science:

• Biochemistry
• Chemical Kinetics
• Free Radical Chemistry

Background:

• Hydroxyl radicals (HO•) are highly reactive species implicated in oxidative damage to biomolecules.
• Understanding the interaction of HO• with proteins is crucial for elucidating cellular damage mechanisms.

Purpose of the Study:

• To investigate the reaction sites of hydroxyl radicals on various proteins using electron spin resonance (e.s.r.) spin trapping.
• To differentiate between backbone and side-chain modifications caused by radical attack.

Main Methods:

• Utilized FeII/H2O2 and CuII/H2O2 redox couples to generate HO• radicals.
• Employed e.s.r. spin trapping with various spin traps, including DMPO (5,5-dimethyl-1-pyrroline N-oxide).
• Applied enzymatic cleavage of protein-radical adducts to analyze smaller nitroxides.

Main Results:

• Anisotropic e.s.r. signals indicated the formation of partially immobilized spin-adducts from HO• attack on proteins.
• DMPO spin trapping allowed differentiation of carbon-, oxygen-, and sulfur-centered radicals based on characteristic spectral values.
• Enzymatic cleavage yielded smaller nitroxides, revealing specific sites of radical damage through beta-proton splittings.
• Results suggest random HO• attack on protein backbones and side chains, consistent with model peptide studies.

Conclusions:

• Hydroxyl radicals attack proteins randomly at both backbone and side-chain residues.
• Spin trapping techniques, particularly with DMPO and subsequent enzymatic cleavage, are effective for mapping radical damage sites.
• The findings provide insights into protein oxidation mechanisms relevant to oxidative stress and disease.