The effects of salt on the TATA binding protein-DNA interaction from a hyperthermophilic archaeon

This study investigates the thermodynamics of the interaction of the TATA box binding protein (TBP) from Pyrococcus woesei (Pw) with an oligonucleotide containing a specific binding site. Pw is a hyperthermophilic archeal organism which exists under conditions of high salt and high temperature. A measurable protein-DNA interaction only occurs at high salt concentrations. Isothermal titration calorimetric binding studies were performed under a range of salts (potassium chloride, potassium phosphate, potassium acetate and sodium acetate) at varying concentrations (0.8 to 1.6 M). At the high salt concentrations used the observed equilibrium binding constant increases with increasing salt concentration. This is very different to the effect reported for all other protein-DNA interactions which have been studied at lower salt concentrations. Thermodynamic data suggest that the protein-DNA interaction at high salt concentration is accompanied by the removal of large numbers of water molecules from the buried hydrophobic surface area. In addition, the involvement of ions appears to influence the binding which can be explained by binding of cations in the interface between the electrostatically negative lateral lobes on the protein and the negatively charged DNA.