Model studies on protein side chain modification by 4-oxo-2-nonenal

Area of Science:

• Biochemistry
• Chemical Biology
• Oxidative Stress Research

Background:

• Lipid peroxidation generates reactive aldehydes like trans-4-oxo-2-nonenal (ONE).
• ONE is implicated in protein modification and cross-linking, contributing to cellular damage.
• Previous work identified ONE's role in Lys-Lys cross-links derived from trans-4-hydroxy-2-nonenal (HNE).

Purpose of the Study:

• To comprehensively investigate the nonoxidative modification of protein nucleophiles by ONE.
• To elucidate the reaction mechanisms and products formed from ONE-protein interactions.
• To compare the cross-linking propensity of ONE with HNE.

Main Methods:

• Utilized 2D NMR spectroscopy to distinguish between 2,3- and 2,4-substituted pyrrole products.
• Investigated the Michael addition of imidazole, thiol, and amine groups to ONE.
• Employed model proteins ribonuclease A and beta-lactoglobulin for cross-linking studies.

Main Results:

• ONE undergoes nonoxidative Michael addition with protein nucleophiles (imidazole, thiol, amine groups) at C2 or C3 positions.
• Formation of 4-keto aldehydes, which subsequently condense with amines to yield nucleophile-substituted pyrroles.
• Major products were 2,3-substituted pyrroles, with minor amounts of 2,4-substituted pyrroles.
• N(tau)-substitution was favored over N(pi)-substitution in histidine Michael addition.
• ONE demonstrated a higher propensity for cross-linking model proteins compared to HNE.

Conclusions:

• ONE nonoxidative modification of proteins involves Michael addition followed by pyrrole formation.
• Reaction mechanisms and product distribution are dependent on the nucleophile and ONE's electrophilic sites.
• ONE is a more potent cross-linking agent than HNE, suggesting significant implications in oxidative stress-related pathologies.