Naphthoquinone–dopamine hybrids disrupt α-synuclein fibrils by their intramolecular synergistic interactions with fibrils and display a better effect on fibril disruption

Abstract

α-Synuclein (αSyn) is an intrinsically disordered protein and its abnormal aggregation into amyloid fibrils is the main hallmark of Parkinson's disease (PD). The disruption of preformed αSyn fibrils using small molecules is considered as a potential strategy for PD treatment. Recent experiments have reported that naphthoquinone–dopamine hybrids (NQDA), synthesized by naphthoquinone (NQ) and dopamine (DA) molecules, can significantly disrupt αSyn fibrils and cross the blood–brain barrier. To unravel the fibril-disruptive mechanisms at the atomic level, we performed microsecond molecular dynamics simulations of αSyn fibrils in the absence and presence of NQDA, NQ, DA, or NQ+DA molecules. Our simulations showed that NQDA reduces the β-sheet content, disrupts K45–E57 and E46–K80 salt-bridges, weakens the inter-protofibril interaction, and thus destabilizes the αSyn fibril structure. NQDA has the ability to form cation–π and H-bonding interactions with K45/K80, and form π–π stacking interactions with Y39/F94. Those interactions between NQDA and αSyn fibrils play a crucial role in disaggregating αSyn fibrils. Moreover, we found that NQDA has a better fibril destabilization effect than that of NQ, DA, and NQ+DA molecules. This is attributed to the synergistic fibril-binding effect between NQ and DA groups in NQDA molecules. The DA group can form strong π–π stacking interactions with aromatic residues Y39/F94 of the αSyn fibril, while the DA molecule cannot. In addition, NQDA can form stronger cation–π interactions with residues K45/K80 than those of both NQ and DA molecules. Our results provide the molecular mechanism underlying the disaggregation of the αSyn fibril by NQDA and its better performance in fibril disruption than NQ, DA, and NQ+DA molecules, which offers new clues for the screening and development of promising drug candidates to treat PD.