Dynamic spin label study of the barstar-barnase complex.

Area of Science:

• Biophysics
• Structural Biology
• Protein Dynamics

Background:

• Understanding protein-protein interactions is crucial for deciphering biological functions.
• The barnase-barstar system serves as a model for studying enzyme-inhibitor complex formation.

Purpose of the Study:

• To investigate protein-protein interactions in the barnase-barstar complex using the dynamic spin label method.
• To assess the mobility of spin labels attached to barstar near the interaction site with barnase.

Main Methods:

• Utilized the dynamic spin label method with Electron Paramagnetic Resonance (EPR) spectroscopy.
• Modified a C40A mutant of barstar with two distinct spin labels at Cys82.
• Analyzed changes in spin label mobility upon complex formation with barnase.

Main Results:

• Formation of the barnase-barstar complex significantly restricted spin label mobility, indicated by increased order parameter (S approaching 1).
• Rotational correlation time (tau) of spin-labeled barstar and its complex matched their molecular weights, suggesting rigid protein entities.
• Spin labels near the barnase-barstar interface experienced restricted mobility due to the protein contact site environment.

Conclusions:

• The dynamic spin label method effectively probes protein-protein interaction interfaces.
• Both barstar and its complex with barnase are conformationally rigid structures.
• This approach is applicable for studying fusion proteins involving barnase or barstar.