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 (tau(c)) and 40 mu s (supra-tau(c) window), strongly influence molecular recognition. This supra-tau(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 mu s. For the first time, this method, performed under super-cooled conditions, enabled us to detect a global motion in the first mu beta-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-tau(c) dynamics. This beta-turn is involved in antibody binding, exhibiting the potential link of the observed supra-tau(c) motion with molecular recognition.