Salt effects on protein-DNA interactions. The lambda cI repressor and EcoRI endonuclease

Area of Science:

• Biophysics
• Computational Biology
• Biochemistry

Background:

• Protein-DNA interactions are crucial for biological processes.
• Electrostatic interactions and salt concentration significantly influence binding affinity.
• Understanding these effects is key to deciphering molecular recognition mechanisms.

Purpose of the Study:

• To calculate the salt-dependent contribution to electrostatic DNA binding free energy for specific protein-DNA complexes.
• To investigate the role of ion atmosphere and local interactions in salt effects.
• To validate the nonlinear Poisson-Boltzmann (NLPB) model against experimental data.

Main Methods:

• Finite-difference solutions of the nonlinear Poisson-Boltzmann (NLPB) equation.
• Calculation of electrostatic DNA binding free energy for lambda cI repressor and EcoRI endonuclease systems.
• Analysis of ion redistribution and its impact on binding stability.

Main Results:

• The NLPB model accurately predicts nonspecific univalent salt-dependent effects on binding free energy, matching experimental results.
• The ion atmosphere significantly destabilizes protein-DNA complexes.
• Global ion redistribution upon binding is a more dominant factor than local protein-DNA interactions (ion-pairs) in determining salt effects.

Conclusions:

• Long-range electrostatic interactions drive significant ion redistribution around proteins and DNA.
• The NLPB model effectively captures salt-dependent effects on protein-DNA complex stability.
• Salt effects, particularly those mediated by ion atmospheres, play a critical role in the relative stability of diverse protein-DNA complexes.