Molecular crowding accelerates aggregation of α-synuclein by altering its folding pathway

Area of Science:

• Biochemistry
• Molecular Biology
• Neuroscience

Background:

• Intracellular macromolecular crowding can promote protein aggregation, particularly for intrinsically disordered proteins like alpha-synuclein.
• Polyethylene glycol (PEG) is used in vitro to mimic crowding effects, with two main hypotheses: excluded volume effect and conformational change.
• Alpha-synuclein aggregation is implicated in neurodegenerative diseases.

Purpose of the Study:

• To differentiate between the excluded volume effect and conformational change hypotheses for alpha-synuclein aggregation in crowded environments.
• To investigate the impact of different polyethylene glycol (PEG) sizes and concentrations on alpha-synuclein aggregation in vitro and in cells.

Main Methods:

• In vitro aggregation assays of alpha-synuclein with varying PEG concentrations and sizes.
• Cell-based assays to observe alpha-synuclein aggregation under crowding conditions.
• Comparative aggregation studies using a globular protein (lysozyme) under similar conditions.

Main Results:

• Increased alpha-synuclein concentration alone does not induce aggregation.
• Smaller PEGs delay fibrillation; larger PEGs (PEG1000, PEG4000, PEG12000) promote nucleation and increase fibril burden.
• PEG4000 reduces aggregation in cells, suggesting environment-specific effects. Globular lysozyme aggregation is unaffected by PEG.

Conclusions:

• Crowding induces aggregation of natively disordered alpha-synuclein by promoting a conformational transition to an aggregation-prone state.
• The effect of crowding on alpha-synuclein aggregation is dependent on PEG size and the cellular environment.
• This conformational transition is specific to intrinsically disordered proteins, not globular ones.