Monomeric α-synuclein binds Congo Red micelles in a disordered manner.

Area of Science:

• Biochemistry
• Biophysics
• Neuroscience

Background:

• Congo Red (CR) is a histological dye known to inhibit alpha-synuclein (aS) fibrillation.
• The precise mechanism of CR's inhibition of aS fibrillation has remained unclear.

Purpose of the Study:

• To elucidate the mode of interaction between Congo Red and alpha-synuclein.
• To understand how CR binding affects aS structure and dynamics.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy, specifically relaxation dispersion measurements.
• Transferred NOE (trNOE) and chemical shift analysis.
• Investigation of salt and pH dependence of the CR-aS interaction.

Main Results:

• At pH 6, CR forms micelles, and only a small fraction (~2%) of aS binds to these micelles at a ~1:1 molar ratio.
• The CR-aS interaction is characterized by rapid exchange kinetics, leading to resonance broadening and attenuation of aS signals.
• The N-terminal residues (1-60) of aS interact electrostatically with CR, while residues 61-100 interact hydrophobically.
• Binding to CR induces a slight increase in helical content in aS, but the protein remains largely disordered.

Conclusions:

• CR does not inhibit aS fibrillation by binding to the free monomeric form of aS.
• The inhibitory effect of CR on aS fibril formation likely arises from its interaction with aggregated forms, such as fibrils or protofibrils.