BPS2026 – Dynamics of protein electrostatics: Critical slowing-down at the interface

It has previously been demonstrated that a small dipolar “mutation” to the protein-water interface of a small globular protein, plastocyanin, can significantly violate the predictions of linear response. The measure of this violation was reported in terms of the so-called effective temperature—a static quantity—and was concurrent with evidence of an interfacial water structural transition through, for example, the splitting of a single energy well into two distinct wells. Additional investigation into the relaxation dynamics of the protein-water system in plastocyanin has revealed 4 orders-of-magnitude of slowing down compared to the wildtype, further indicating a nearby critical point and offering a plausible mechanism by which the equilibrium Arrhenius rate picture can be modified by biological systems. A range of magnitudes of the dipolar order parameter were explored, revealing the broad extent of critical slowing down and the existence of two separate relaxation regimes on either side of the critical perturbation.