Atomic Resolution Insight into Sac7d Protein Binding to DNA and Associated Global Changes by Molecular Dynamics Simulations

Sac7d is a small, thermostable protein that induces large helical deformations in DNA upon association. Starting from multiple initial placements of the unbound Sac7d structure relative to a B-DNA oligonucleotide, molecular dynamics (MD) simulations were employed to directly follow several successful binding events at atomic resolution that resulted in structures in close agreement with the native complex geometry. The final native complex formed rapidly within tenths of nanoseconds and included simultaneous large-scale kinking, groove opening, twisting, and intercalation in the target DNA. The simulations indicate that the complex formation process involves initial non-native contacts that helped in reaching the final bound state, with residues intercalated at the center of the kinked DNA. It was also possible to identify several long-lived trapped intermediate states of the binding process and to follow sliding processes of Sac7d along the DNA minor groove.