3-Hydroxylysine, a potential marker for studying radical-induced protein oxidation

Area of Science:

• Biochemistry
• Oxidative Stress Research
• Protein Chemistry

Background:

• Gamma-irradiation of amino acids in the presence of oxygen generates hydroperoxides.
• Previous work identified valine and leucine hydroperoxides/hydroxides in biological systems and diseased tissues.
• Lysine residues are surface-exposed and susceptible to radical oxidation.

Purpose of the Study:

• To investigate oxidized lysine as a sensitive marker for protein oxidation.
• To identify specific hydroxylysine products formed from lysine oxidation.
• To evaluate the utility of hydroxylysines as markers for radical-mediated protein oxidation.

Main Methods:

• Gamma-irradiation of lysine in the presence of oxygen, followed by sodium borohydride (NaBH4) reduction.
• High-performance liquid chromatography (HPLC) analysis of 9-fluorenylmethyl chloroformate (FMOC) derivatives for quantification.
• Detection of hydroxylysines in hydrolysates of oxidized peptides and proteins (e.g., bovine serum albumin, histone H1).

Main Results:

• HO* attack on lysine yields 3-hydroxylysine, 4-hydroxylysine, and 5-hydroxylysines.
• 5-Hydroxylysines are natural products and not suitable markers for radical oxidation.
• 3- and 4-Hydroxylysines are identified as useful markers; their yields are higher in surface-exposed residues compared to hydrophobic residues like valine and leucine in globular proteins.

Conclusions:

• Hydroxylysines, particularly 3-hydroxylysine, are sensitive and valuable markers of radical-mediated protein oxidation.
• Quantification of hydroxylysines provides a method to assess protein damage in biological systems.
• Surface-exposed amino acid residues are more susceptible to oxidation than hydrophobic residues.