Oxidant-Mediated Protein Amino Acid Conversion

Area of Science:

• Biochemistry
• Molecular Biology
• Oxidative Stress

Background:

• Biological oxidation, particularly protein carbonylation, is implicated in disease pathogenesis and aging.
• Specific amino acids like arginine (Arg) and proline (Pro) are susceptible to carbonylation, yielding glutamyl semialdehyde.
• While chemically irreversible, biological systems may reduce glutamyl semialdehyde back to Pro within proteins.

Purpose of the Study:

• To hypothesize that biological oxidation can post-translationally convert Arg to Pro, Arg to Glu, and Pro to Glu within protein structures.
• To investigate the potential for amino acid conversions beyond DNA sequence dictates.
• To explore the functional implications of non-DNA coded amino acid sequences.

Main Methods:

• Utilizing mass spectrometry to analyze protein modifications in human cells.
• Quantifying the extent of amino acid replacement in specific proteins, such as peroxiredoxin 6.
• Investigating redox regulation mechanisms potentially driving these conversions.

Main Results:

• Mass spectrometry data revealed that 5-10% of peroxiredoxin 6 molecules in human cells exhibit a Pro-45 to Glu replacement.
• Experimental evidence suggests biological systems can facilitate the reduction of glutamyl semialdehyde to Pro.
• Glutamyl semialdehyde can be further oxidized to glutamic acid (Glu).

Conclusions:

• Biological oxidation can lead to post-translational conversion of amino acids within proteins, challenging the central dogma of molecular biology.
• Amino acid replacements via redox regulation can result in proteins with non-DNA coded sequences, conferring novel functions.
• This discovery opens new avenues for understanding protein diversity and function in health and disease.