Minima and Barriers on the Pressure-Temperature Free Energy Landscape of Phosphoglycerate Kinase

Abstract

Proteins can exhibit strikingly different free energy landscapes depending on which thermodynamic variable is manipulated to study folding. We have investigated the relationship between temperature- and pressure-induced denaturation of yeast phosphoglycerate kinase (PGK). Thermodynamically, the pressure-temperature phase diagram of PGK seems standard: with a slight deviation from two-state behavior at low temperatures, a predicted elliptical shape of stability emerges. Kinetically, the behavior is much more complex: although a temperature perturbation of the energy landscape of PGK reveals a multitude of barriers, pressure-jump experiments spanning timescales from microsecond to hours showed only one predominant several-minute-long kinetic phase. These observations may indicate that under pressure, the smaller kinetic barriers of PGK are smoothed out by the large positive activation volume of the transition state.