Multi-Probe Equilibrium Analysis of Gradual (Un)Folding Processes.

Area of Science:

• Biochemistry
• Biophysics
• Spectroscopy

Background:

• Studying gradual protein unfolding provides insights into intermediate folding stages.
• Characterizing these intermediate states requires site-specific structural probes.
• Isotopically edited infrared (IR) spectroscopy offers high-resolution structural information.

Purpose of the Study:

• To describe methods for synthesizing ¹³C isotopically edited protein samples.
• To detail experimental IR spectroscopic measurements for protein unfolding.
• To analyze site-specific equilibrium thermal unfolding using temperature-dependent IR data.

Main Methods:

• Chemical synthesis of proteins with site-specific ¹³C labeling.
• ¹³C labeling of amide carbonyls to create detectable side-bands in IR spectra.
• Utilizing amide I' vibrations sensitive to local conformation and solvent exposure.

Main Results:

• ¹³C labeling enables site-specific structural probes without perturbing protein structure.
• Temperature-dependent IR data allows analysis of equilibrium thermal unfolding.
• High-resolution structural information on protein folding intermediates is obtained.

Conclusions:

• Isotopically edited IR spectroscopy is a powerful tool for studying protein folding.
• This methodology provides detailed insights into rarely accessible intermediate stages.
• The described procedures facilitate the characterization of small protein unfolding.