Alpha-synuclein structures probed by 5-fluorotryptophan fluorescence and 19F NMR spectroscopy

Area of Science:

• Biochemistry
• Structural Biology
• Neuroscience

Background:

• Alpha-synuclein is the primary protein in Parkinson's disease (PD) aggregates.
• In vitro, alpha-synuclein exists as an intrinsically disordered protein.
• Understanding its conformation is crucial for PD pathogenesis research.

Purpose of the Study:

• To investigate the site-specific conformation of alpha-synuclein.
• To utilize biosynthetic incorporation of unnatural amino acids for structural probing.
• To characterize the protein's structure in solution using advanced spectroscopic techniques.

Main Methods:

• Biosynthetic incorporation of 5-fluorotryptophan (5FW), an unnatural amino acid, into recombinant alpha-synuclein.
• Site-specific labeling at positions 4, 39, and 94.
• Characterization using fluorescence spectroscopy (steady-state emission, excited-state decays) and 19F Nuclear Magnetic Resonance (NMR) spectroscopy.

Main Results:

• Fluorescence spectroscopy indicated that the indole side chains of 5FW at all three positions are exposed to the aqueous environment.
• Excited-state decay analysis revealed virtually identical single-exponential decays, suggesting similar local environments.
• 19F NMR spectroscopy showed single resonance peaks for each labeled site, further supporting structural homogeneity near the probes.

Conclusions:

• The protein conformations of alpha-synuclein are highly similar in the vicinity of positions 4, 39, and 94.
• These findings provide site-specific structural insights into the disordered state of alpha-synuclein.
• The methodology enables detailed conformational analysis of intrinsically disordered proteins relevant to neurodegenerative diseases.