Amides are novel protein modifications formed by physiological sugars

Area of Science:

• Biochemistry
• Chemical Biology
• Pathophysiology

Background:

• The Maillard reaction produces advanced glycation end products (AGEs) in vivo, linked to various pathologies.
• Establishing the in vivo structures of AGEs remains challenging despite extensive research.

Purpose of the Study:

• To identify and characterize novel amide protein modifications resulting from the Maillard reaction.
• To elucidate the formation pathways and precursors of these new AGEs.
• To assess the potential of these modifications as biomarkers in pathophysiological conditions.

Main Methods:

• Independent synthesis and coupled liquid chromatography/mass spectrometry for structural confirmation.
• Model reactions using protected lysine derivatives to study reaction mechanisms.
• Utilizing advanced glycation end product inhibitors (aminoguanidine, pyridoxamine) to dissect formation pathways.
• Enzymatic hydrolysis of brunescent lens protein to quantify GOLA levels.

Main Results:

• N(6)-[2-[(5-amino-5-carboxypentyl)amino]-2-oxoethyl]lysine (GOLA) and N(6)-glycoloyllysine (GALA) were identified as novel amide protein modifications.
• Glyoxal and glycolaldehyde were confirmed as immediate precursors, with pathways linked to N(epsilon)-carboxymethyllysine.
• GOLA and GALA formation involves oxidation of the Amadori product or glyoxal-imine intermediates.
• GOLA was detected in brunescent lens protein, indicating its presence in vivo.

Conclusions:

• Amide protein modifications like GOLA and GALA represent new classes of AGEs.
• Their formation pathways are linked to reactive carbonyl species and oxidative processes.
• These novel AGEs may serve as significant biomarkers for understanding and diagnosing pathophysiological processes.