Kinetics of the Antibody Recognition Site in the Third IgG-Binding Domain of Protein G

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• Protein dynamics across various timescales are vital for protein function.
• Motions within the supra-rotational correlation time (supra-τc) window (between globular rotational correlation time and 40 μs) are critical for molecular recognition.
• Experimental methods to probe dynamics in the supra-τc window were previously lacking.

Purpose of the Study:

• To develop and apply a novel experimental method for measuring fast kinetic processes in proteins.
• To investigate protein dynamics in the supra-τc window.
• To explore the functional implications of these dynamics in molecular recognition.

Main Methods:

• Development of a high-power relaxation dispersion (RD) experiment capable of measuring kinetics as fast as 4 μs.
• Application of the RD experiment under super-cooled conditions.
• Analysis of model-free residual dipolar coupling (RDC) order parameters and ensemble dynamics.

Main Results:

• Detection of a global motion in the first β-turn of the IgG-binding domain of protein G (GB3) using the novel RD experiment.
• Extrapolation of this motion to 371±115 ns at 310 K.
• Observation of plasticity in RDC order parameters and supra-τc dynamics within the same β-turn residues.

Conclusions:

• The developed RD experiment successfully probes dynamics in the previously hidden supra-τc window.
• A significant global motion in a GB3 β-turn, involved in antibody binding, was identified.
• The findings suggest a direct link between supra-τc protein dynamics and molecular recognition processes.