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

Protein dynamics occurring on a wide range of timescales play a crucial role in governing protein function. Particularly, motions between the globular rotational correlation time ( τ c ) and 40 μs (supra‐ τ c window), strongly influence molecular recognition. This supra‐ τ c window was previously hidden, owing to a lack of experimental methods. Recently, we have developed a high‐power relaxation dispersion (RD) experiment for measuring kinetics as fast as 4 μs. For the first time, this method, performed under super‐cooled conditions, enabled us to detect a global motion in the first β‐turn of the third IgG‐binding domain of protein G (GB3), which was extrapolated to 371±115 ns at 310 K. Furthermore, the same residues show the plasticity in the model‐free residual dipolar coupling (RDC) order parameters and in an ensemble encoding the supra‐ τ c dynamics. This β‐turn is involved in antibody binding, exhibiting the potential link of the observed supra‐ τ c motion with molecular recognition.