Structural interplay between DNA-shape protein recognition and supercoiling: The case of IHF

The integration host factor (IHF) is a prominent example of indirect readout as it imposes one of the strongest bends on relaxed linear DNA. However, the relation between IHF and torsionally constrained DNA, as occurs physiologically, remains unclear. By using atomistic molecular dynamics simulations on DNA minicircles, we reveal, for the first time, the reciprocal influence between a DNA-bending protein and supercoiling. On one hand, the increased curvature of supercoiled DNA enhances wrapping around IHF making the final complex topologically dependent. On the other hand, IHF acts as a ’supercoiling relief’ factor by compacting relaxed DNA loops and, when supercoiled, it pins the position of plectonemes in a unique and specific manner. In addition, IHF restrains under- or overtwisted DNA depending on whether the complex is formed in negatively or positively supercoiled DNA, becoming effectively a ‘supercoiling buffer’. We finally provide evidence of DNA bridging by IHF and reveal that these bridges divide DNA into independent topological domains. We anticipate that the crosstalk detected here between the ‘active’ DNA and the multifaceted IHF could be common to other DNA–protein complexes relying on the deformation of DNA.