Evaluation of dissociation constants from competition binding experiments based on the relative binding ratio

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Protein-DNA interactions are fundamental to cellular processes.
• Accurate quantification of binding affinities is crucial for understanding these interactions.
• Existing methods for determining dissociation constants can be complex.

Purpose of the Study:

• To present a simplified procedure for quantitative evaluation of dissociation constants in protein-DNA binding.
• To introduce self-competition experiments as a complementary method for assessing protein conformational purity.
• To provide a robust method for checking the conformational integrity of DNA-binding proteins.

Main Methods:

• Developed a competition binding assay for quantitative evaluation of dissociation constants.
• Derived equations relating the ratio of bound DNA probe to competitor concentration.
• Utilized self-competition titration in conjunction with direct titration.

Main Results:

• Demonstrated that the ratio of bound DNA probe to protein is a linear function of competitor concentration at high concentrations.
• Derived equations to calculate the dissociation constant of the protein-competitor complex from the slope of this linear function.
• Showed that self-competition titration can determine the fraction of correctly folded protein capable of specific DNA binding.

Conclusions:

• The presented competition binding assay offers a straightforward method for determining dissociation constants.
• Combining direct and self-competition titrations provides a reliable check for the conformational purity of DNA-binding proteins.
• This approach enhances the accuracy and reliability of studying protein-DNA associations.