Double-mutant Thermodynamic Cycles under High Hydrostatic Pressure

Abstract

Double-mutant thermodynamic cycle analysis has proved to be a unique method for providing quantitative information on the effects of a second mutation on equilibrium and kinetic processes, and thus on the interactions between two residues. Because volume changes reflect free energy changes along a reaction pathway, high pressure thermodynamic analysis of the double mutant-cycle can be used for investigating ‘volumetric interaction’ between amino acid residues. We applied this approach for analyzing the effects of site-directed mutations on the structural and catalytic properties of a model enzyme, human butyrylcholinesterase. The ‘coupling volume’ between the pair of mutations on two key residues allowed the interaction of the two mutated residues in wild-type enzyme to be measured. This provided information on conformation equilibrium between two forms of the enzyme and volumetric, conformational and pulsed hydration changes along the enzyme-catalyzed hydrolysis pathway of a neutral ester.