Calculation of binding free energies.

Molecular dynamics simulations enable access to free energy differences governing the driving force underlying all biological processes. In the current chapter we describe alchemical methods allowing the calculation of relative free energy differences. We concentrate on the binding free energies that can be obtained using non-equilibrium approaches based on the Crooks Fluctuation Theorem.

A designed conformational shift to control protein binding specificity.

In a conformational selection scenario, manipulating the populations of binding-competent states should be expected to affect protein binding. We demonstrate how in silico designed point mutations within the core of ubiquitin, remote from the binding interface, change the binding specificity by shifting the conformational equilibrium of the ground-state ensemble between open and closed substates that have a similar population in the wild-type protein. Binding affinities determined by NMR titration experiments agree with the predictions, thereby showing that, indeed, a shift in the conformational equilibrium enables us to alter ubiquitin's binding specificity and hence its function.