Elucidating factors important for monovalent cation selectivity in enzymes: E. coli β-galactosidase as a model.

Many enzymes require a specific monovalent cation (M(+)), that is either Na(+) or K(+), for optimal activity. While high selectivity M(+) sites in transport proteins have been extensively studied, enzyme M(+) binding sites generally have lower selectivity and are less characterized. Here we study the M(+) binding site of the model enzyme E.

Na(+), K (+) and Tl(+) hydration from QM/MM computations and MD simulations with a polarizable force field.

The hydration of three different monovalent cations was studied with a number of theoretical approaches ranging from classical MD simulations to MD simulations with a polarizable force field and finally to QM/MM MD. A particular emphasis was put on the development of a novel polarizable potential function for studies of Tl(+) hydration enabling the ability to reproduce key features observed in QM/MM simulations. We extended the CHARMM-deMon interface developed previously to studies of ion hydration with QM/MM simulations.