Impact of glucagon oxidation on fibril formation

Abstract

Glucagon structural dynamics is crucial for its function and pathology, yet its oligomerization and fibrillization mechanisms remain unclear. The early assembly of glucagon into fibrils is a critical process that can be perturbed by oxidation at key residues. In this study, we systematically tracked the oligomer formation of native glucagon up to the decamer level, revealing that glucagon undergoes oxidation at tryptophan and methionine—residues essential to its steric zipper structure. Our findings also indicate that oxidation exerts a dual effect on glucagon fibrillation. At low concentrations, oxidation partially unfolds glucagon's α-helix, facilitating hetero-oligomer formation between oxidized and native peptides, which promotes further oligomerization and unfolding. However, at high concentrations, oxidized glucagon fails to self-assemble into fibrils and appears more susceptible to degradation. Chromatographic analysis differentiates native and oxidized glucagon, highlighting increased polarity and multiple elution peaks indicative of diverse oxidative states, while mass spectrometry confirms site-specific modifications that influence structural transitions. These results emphasize the fine balance between oxidation and self-assembly, with implications for glucagon's therapeutic stability. An understanding of oxidation-induced aggregation dynamics is essential for developing stable glucagon formulations, underscoring the importance of controlling oxidative conditions to preserve their functionality and efficacy.