Liquid-liquid phase separation of α-synuclein is highly sensitive to sequence complexity

Area of Science:

• Biochemistry
• Neuroscience
• Molecular Biology

Background:

• Alpha-synuclein (α-syn) protein aggregation is linked to Parkinson's disease.
• Alpha-synuclein undergoes liquid-liquid phase separation (LLPS), a process often preceding amyloid fibril formation.
• Distinguishing the roles of LLPS from fibrillation in α-syn pathology is challenging due to their frequent co-occurrence.

Purpose of the Study:

• To identify molecular determinants specifically regulating α-syn LLPS, independent of fibrillation.
• To investigate the role of sequence complexity in modulating α-syn LLPS.
• To develop strategies for selectively perturbing α-syn LLPS or fibrillation.

Main Methods:

• Utilized subtle missense mutations in α-syn to alter sequence complexity.
• Quantified changes in LLPS propensity based on specific mutations.
• Assessed the correlation between LLPS and amyloid fibril formation for different α-syn variants.

Main Results:

• Alpha-synuclein LLPS is highly sensitive to its sequence complexity.
• A conservative V16I mutation increasing complexity reduced LLPS by 75%, reversible by V15I mutation.
• The Parkinson's-associated A18T mutation, enhancing complexity, also reduced LLPS, suggesting a role in pathogenicity.
• Demonstrated that α-syn fibrillation does not always correlate with LLPS, identifying mutations that selectively affect one process over the other.

Conclusions:

• Sequence complexity is a critical determinant of α-syn LLPS.
• The ability to selectively perturb LLPS or fibrillation opens new avenues for research.
• Findings provide tools to disentangle the distinct roles of α-syn LLPS and fibrillation in Parkinson's disease pathogenesis.