Changes in the Aqueous Solvent do not Impact the Internal Ring-Flip Dynamic of Fully Buried F52 in Protein GB1

Aromatic ring flips are a hallmark of protein dynamics. They are mediated by either transient "breathing" motions in which the protein expands into the solvent or by transient internal rearrangement of void spaces. Therefore, they are excellent reporters of such transient protein fluctuations. To decipher the extent to which ring-flip dynamics are governed by the protein itself or by the aqueous solvent around it, the ring flip of the fully buried aromatic side chain of F52 in protein B1 domain of immunoglobulin G binding protein G(GB1) with experimentally feasible altered buffer conditions by nuclear magnetic resonance relaxation dispersion experiments is studied. Herein, it is found that ring-flip rate constants remain the same in all studied cases. Therefore, the ring-flip dynamic in the interior of GB1 is independent from the solvent and only depends on the protein itself. In addition, this study shows that ring flips are comparable within different buffer conditions.