Structural transitions in the protein L denatured state ensemble

Area of Science:

• Protein folding dynamics
• Biophysical characterization of protein structure
• Protein L structural transitions

Background:

• Understanding protein folding is crucial for deciphering biological function.
• The denatured state ensemble of proteins may contain residual structures.
• Protein L serves as a model system for studying protein folding.

Purpose of the Study:

• To investigate the extent and timescale of structural transitions in the denatured state ensemble of protein L.
• To identify regions with residual structure in the unfolded state of protein L.
• To elucidate the interactions responsible for residual structure in protein L.

Main Methods:

• Amide proton exchange measurements
• Fluorescence spectroscopy (tryptophan fluorescence, fluorescence energy transfer)
• Circular dichroism (CD) spectroscopy
• Stopped-flow kinetics

Main Results:

• Weak amide proton exchange protection observed in the first beta-hairpin and helix during refolding.
• Tryptophan fluorescence indicated partial ordering in the first beta-hairpin of protein L in the unfolded state.
• Fluorescence energy transfer and stopped-flow studies revealed submillisecond refolding kinetics.
• CD spectroscopy of peptides suggested specific interactions contributing to residual structure.

Conclusions:

• Protein L exhibits residual structure in its denatured state ensemble, particularly in the first beta-hairpin and helix.
• These residual structures form and transition on submillisecond timescales.
• Specific peptide interactions likely stabilize these partially ordered states in the unfolded ensemble.