Mechanistic contributions of the lipid peroxidation product 4-hydroxynonenal on amyloid self-assembly and associated cytotoxicity

¹Department of Chemistry, Université du Québec à Montréal, Montréal, Qc, CANADA
²Quebec Network for Research on Protein Function, Engineering, and Applications, PROTEO

Non-enzymatic post-translational modifications of proteins can lead to a change in the chemical nature of residue side chains through different mechanisms and often leads to a large perturbation of protein structure, stability and function. 4-Hydroxynonenal (HNE) is one of the major products of lipid peroxidation and among the most studied, owing to its reactivity with various biomacromolecules. Most of the biochemical effects of HNE can be explained by its rapid formation of covalent adducts with thiol and amino groups, resulting in altered physicochemical properties. High levels of HNE in pancreatic islets of diabetic patients could modulate the formation of amyloid fibrils, whose main constituent is the islet amyloid polypeptide (IAPP).In this study, wedefined the mechanistic relationships between HNE and IAPP amyloidogenesis. LC-MS/MS analysis revealed a selective modification of IAPP at His-18 imidazole side chain by HNE. To model this covalent modification, IAPP was modified by introducing an alkyl substitute on the imidazole N(π)-position of histidine using the octanoyl chain. IAPP bearing a lipid chain on the His side chain exhibited a hastened conformational conversion from monomeric random coil to β-sheet-rich fibrillar states, as revealed by fluorescence, circular dichroism spectroscopy, atomic force microscopy and transmission electronic microscopy. Site-specific histidine lipidation also induced the deposition of unmodified IAPP by reshaping the aggregation pathway. These results illustrate that HNE lipidation increases the hydrophobicity of the peptide and it may therefore play an initiating role inthe membrane perturbation and associated cell death.