Energetics of subunit dimerization in bacteriophage lambda cI repressor: linkage to protons, temperature, and KCl

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Protein oligomerization and DNA binding are crucial for gene regulation.
• Understanding the energetic contributions to protein assembly is essential for characterizing cooperativity and site specificity.

Purpose of the Study:

• To investigate the effects of temperature, proton activity, and monovalent salt on lambda cI repressor monomer-dimer assembly.
• To characterize the chemical forces driving subunit association and stabilization.

Main Methods:

• Utilized a novel gel chromatographic procedure for high-sensitivity measurements.
• Studied monomer-dimer assembly of lambda cI repressor across a range of pH, temperature, and salt concentrations.

Main Results:

• Dimerization involves proton absorption and is temperature-dependent.
• The dimerization reaction exhibits a significant negative enthalpy of association.
• Monovalent salt concentration influences subunit association, with weaker association at lower salt levels.
• Repulsive interactions between negatively charged residues are mitigated by increasing KCl concentrations.

Conclusions:

• The lambda cI repressor dimer interface formation is influenced by proton and ion binding.
• Cation absorption likely stabilizes the dimer complex.
• These findings provide insights into the chemical forces governing protein-DNA interactions in gene regulation.