Molecular dynamics simulations of the tetracycline-repressor protein: the mechanism of induction

Molecular dynamics simulations on the tetracycline-repressor (TetR) protein, both in the absence of an inducer and complexed with the inducers tetracycline and 5a,6-anhydrotetracycline, show significant differences in the structures and dynamics of the induced and non-induced forms of the protein. Calpha-density-difference plots, low-frequency normal vibrations and inter-residue interaction energies all point to a common mechanism of induction. The inducer displaces Asp156 from the magnesium ion in the binding pocket, leading to a short cascade of rearrangements of salt bridges that results in the allosteric change. The increased flexibility of the induced form of the protein is suggested to contribute to the decrease in binding affinity to DNA on induction.