Protein global fold determination using site-directed spin and isotope labeling

Area of Science:

• Structural Biology
• Biophysics
• Protein Science

Background:

• Determining protein global folds is crucial for understanding protein function.
• Existing methods can be time-consuming or require extensive data.
• A rapid and accurate method for protein structure determination is needed.

Purpose of the Study:

• To develop and validate a simple experimental approach for rapid determination of protein global folds.
• To utilize site-directed spin labeling (SDSL) and isotope enrichment for distance restraint determination.
• To demonstrate the precision and accuracy of this method on a well-characterized protein, barnase.

Main Methods:

• Site-directed spin labeling (SDSL) with a nitroxide spin label (MTSSL) on 15N-enriched barnase derivatives.
• Measurement of amide proton longitudinal relaxation times in oxidized and reduced states.
• Calculation of long-range distance restraints (8-35 Å) using paramagnetic effects and correlation times.
• Structure calculations incorporating paramagnetic distance restraints and secondary structure information.

Main Results:

• Demonstrated the feasibility of calculating protein global folds using only paramagnetic effects.
• Achieved backbone RMSDs <3 Å from the crystal structure for barnase.
• Validated the accuracy and precision of the SDSL-based approach for protein structure determination.
• Successfully obtained overall protein topology using limited paramagnetic distance restraints.

Conclusions:

• The described experimental approach enables rapid determination of protein global folds.
• This method provides accurate structural information using paramagnetic effects from spin labels.
• The technique offers a valuable tool for efficiently characterizing protein structures and topologies.