Structural Dynamics of the Bacillus subtilis MntR Transcription Factor Is Locked by Mn(2+) Binding

Manganese (II) ions are essential for a variety of bacterial cellular processes. The transcription factor MntR is a metallosensor that regulates Mn(2+) ion homeostasis in the bacterium Bacillus subtilis. Its DNA-binding affinity is increased by Mn(2+) ion binding, allowing it to act as a transcriptional repressor of manganese import systems. Although experimentally well-researched, the molecular mechanism that regulates this process is still a puzzle. Computational simulations supported by circular dichroism (CD), differential scanning calorimetry (DSC) and native gel electrophoresis (native-PAGE) experiments were employed to study MntR structural and dynamical properties in the presence and absence of Mn(2+) ions. The results of molecular dynamics (MD) simulations revealed that Mn(2+) ion binding reduces the structural dynamics of the MntR protein and shifts the dynamic equilibrium towards the conformations adequate for DNA binding. Results of CD and DSC measurements support the computational results showing the change in helical content and stability of the MntR protein upon Mn(2+) ion binding. Further, MD simulations show that Mn(2+) binding induces polarization of the protein electrostatic potential, increasing the positive electrostatic potential of the DNA-binding helices in particular. In order to provide a deeper understanding of the changes in protein structure and dynamics due to Mn(2+) binding, a mutant in which Mn(2+) binding is mimicked by a cysteine bridge was constructed and also studied computationally and experimentally.