Mapping of Photochemically-Derived Dityrosine across Fe-Bound N-Acetylated α-Synuclein

Parkinson’s disease (PD) is the second most common neurological disease and belongs to a group of neurodegenerative disorders called synucleinopathies in which pathological aggregates of N-terminally acetylated α-synuclein ((NAc)α-Syn) accumulate in various regions of the brain. In PD, these (NAc)α-Syn aggregates have been found to contain covalent dityrosine crosslinks, which can occur either intermolecularly or intramolecularly. Cerebral metal imbalance is also a hallmark of PD, warranting investigations into the effects of brain biometals on (NAc)α-Syn. (NAc)α-Syn is an intrinsically disordered protein, and metal-mediated conformational modifications of this structurally dynamic protein have been demonstrated to influence its propensity for dityrosine formation. In this study, a library of tyrosine-to-phenylalanine (Y-to-F) (NAc)α-Syn constructs were designed in order to elucidate the nature and the precise residues involved in dityrosine crosslinking of Fe-bound (NAc)α-Syn. The structural capacity of each mutant to form dityrosine crosslinks was assessed using Photo-Induced Cross-Linking of Unmodified Proteins (PICUP), demonstrating that coordination of either Fe(III) or Fe(II) to (NAc)α-Syn inhibits dityrosine crosslinking among the C-terminal residues. We further demonstrate that Y39 is the main contributor to dityrosine formation of Fe-bound (NAc)α-Syn, while Y125 is the main residue involved in dityrosine crosslinks in unmetalated (NAc)α-Syn. Our results confirm that iron coordination has a global effect on (NAc)α-Syn structure and reactivity.