α-Synuclein is an intrinsically disordered protein (IDP). The aggregation of α-synuclein is associated with several neurodegenerative diseases like Parkinson’s disease (PD). During the process of aggregation, α-synuclein interacts with biomolecules and forms liquid-liquid phase separation (LLPS), which will lead to calcium dysregulation and mitochondrial dysfunction. Mitochondria provide more than 90% of energy to support bioreactions inside cells. Mitochondrial DNA (mtDNA), which is always covered by mitochondrial nucleoid protein TFAM, is a double-stranded circular DNA with various copies in the mitochondrial matrix. In PD models, α-synuclein has been reported to import into mitochondria and interact with several mitochondrial proteins. However, the relationships among α-synuclein, mtDNA, and TFAM remain unclear. Our study first shows α-synuclein is colocalized with TFAM in mitochondria and confirms TFAM interacts with α-synuclein both in vivo and in vitro. Furthermore, we also observed TFAM, α-synuclein, and mtDNA could form LLPS in a calcium-dependent manner. Then, we demonstrate that α-synuclein is the backbone protein for LLPS droplet and the structure conversion of α-synuclein is specific in calcium conditions. Finally, we applied this model on the single-molecule optical tweezers. We find α-synuclein could weaken the binding between TFAM and mtDNA based on the rip events analysis in force-distance curves. Moreover, we also demonstrate α-synuclein could grab TFAM from mtDNA by fluorescence polarization. Our study combined biochemical and biophysical methods to study the biomolecular interaction at single-molecule level. Furthermore, this finding sheds light on molecular mechanisms in PD and provides potential targets for PD treatments.
Xu et al. (Sun,) studied this question.