Isoform-specific oxidative modifications of tropoelastin by HOCl and MPO alter protein self-assembly

Tropoelastin (TE), the soluble precursor of elastin, is critical for the elasticity of arteries, lungs, and skin. Oxidative damage to TE has been implicated in vascular diseases, but the isoform-specific effects remain poorly understood. Hypochlorous acid (HOCl), generated by the enzyme myeloperoxidase (MPO) targets extracellular matrix proteins during inflammatory processes. However, the differential susceptibility and functional consequences in specific TE isoforms are unknown.

We investigated the effects of HOCl and MPO-derived oxidants on two human TE isoforms, TE2 and TE6. Oxidative modifications were analyzed using high-resolution LC-MS/MS, with site-specific identification of chlorinated tyrosines and oxidized cysteine residues. Functional consequences were assessed using turbidity-based coacervation assays.

TE2 exhibited chlorination at multiple tyrosine residues, particularly 3,5-dichlorotyrosine, while showing minimal cysteine oxidation. In contrast, TE6 was more oxidised at its single disulfide bond, resulting in irreversible sulfonic acid formation. These isoform-specific patterns translated into functional differences: TE2 demonstrated enhanced coacervation , whereas TE6 showed reduced assembly capacity, consistent with structural destabilization.

HOCl and MPO-derived oxidants induce distinct modifications in tropoelastin isoforms, resulting in divergent effects on protein self-assembly. These findings highlight the importance of isoform context in extracellular matrix remodeling under oxidative stress and may have implications for vascular pathologies.