19F NMR-based solvent accessibility profiling reveals tryptophan ring-flip dynamics in a protein
Soichiro Kawagoe1, Hiroyuki Kumeta2, Tomohide Saio1,3
1Institute of Advanced Medical Sciences, Tokushima University, Tokushima, Japan.
Protein Science : a Publication of the Protein Society
|September 13, 2025
Summary
Tryptophan flipping in proteins, often overlooked, is revealed by a novel 19F NMR method. This technique tracks Trp23 dynamics in heat shock factor 1, showing its conformational flexibility.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Aromatic ring flipping is crucial for protein dynamics and breathing motions.
- Tryptophan flipping is less understood than phenylalanine or tyrosine due to its bulk and indole structure.
- Heat shock factor 1 (Hsf1) is a key transcriptional regulator involved in cellular stress response.
Purpose of the Study:
- To develop and apply a 19F NMR-based approach to investigate tryptophan flipping dynamics.
- To characterize the conformational states and dynamics of Trp23 in the Hsf1 DNA-binding domain (DBD).
- To establish a novel method for probing aromatic ring flipping and solvent accessibility in proteins.
Main Methods:
- Incorporation of 5-fluorotryptophan into the Hsf1 DBD.
- 19F NMR spectroscopy to monitor Trp23 flipping in solution.
- Temperature-dependent analysis, relaxation dispersion, D2O isotope shifts, and solvent paramagnetic relaxation enhancement experiments.
Main Results:
- 19F NMR confirmed Trp23 undergoes dynamic flipping between distinct conformers.
- Interconversion between flip-in (buried) and flip-out (solvent-exposed) states was observed.
- 19F NMR-based solvent accessibility profiling was successfully applied to study aromatic ring flipping.
Conclusions:
- Trp23 in Hsf1 DBD dynamically flips between buried and solvent-exposed states in solution.
- The 19F NMR strategy provides a powerful tool for studying aromatic ring dynamics in proteins.
- This method opens new avenues for investigating protein conformational flexibility and function.
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