X-ray structural and simulation analysis of a protein mutant: The value of a combined approach

The effect of the mutation Arg 96 to His on the stability of bacteriophage T4 lysozyme has been previously studied by calorimetric expts., X-ray crystallog., and free energy simulation techniques.  The exptl. and calcd. values for the difference between the free energy of denaturation of the mutant and the wild type are in reasonable agreement.  However, the two approaches led to different explanations for the loss in stability.  To analyze the differences, a series of refinements based on the crystallog. data were performed, a no. of aspects of the simulations were reexamd., and continuum electrostatic calcns. were done to complement the latter.  The results of those comparisons provide a better understanding of the origin of the free energy difference in this mutant.  Furthermore, they show the importance of the combined use of simulations and crystallog. for interpreting the effects of mutations on the energetics of the system.