SSB-DNA binding monitored by fluorescence intensity and anisotropy

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Protein-DNA interactions are fundamental to biological processes.
• Fluorescence spectroscopy offers sensitive detection of these interactions.
• Understanding binding stoichiometry and affinity is crucial for elucidating interaction mechanisms.

Purpose of the Study:

• To present fluorescence-based methodologies for quantifying protein-DNA binding equilibria.
• To determine the occluded site size and binding affinities of Escherichia coli and Deinococcus radiodurans SSB proteins with single-stranded DNA (ssDNA).
• To demonstrate data analysis and modeling for fluorescence intensity and anisotropy measurements.

Main Methods:

• Utilizing intrinsic tryptophan fluorescence and extrinsic fluorophore labeling.
• Monitoring changes in fluorescence intensity and anisotropy upon protein-DNA binding.
• Applying equilibrium binding models to analyze data from ssDNA binding studies.
• Investigating the influence of solution conditions (salt concentration and type) on binding.

Main Results:

• Established procedures for determining stoichiometries and equilibrium binding affinities of SSB proteins.
• Quantified occluded site sizes for SSB binding to polymeric ssDNA.
• Provided examples of quantitative analysis for SSB binding to oligonucleotides.
• Highlighted the impact of salt concentration on binding affinity and mode.

Conclusions:

• Fluorescence methods are powerful tools for quantitative analysis of protein-DNA interactions.
• Accurate determination of binding parameters requires appropriate data analysis and consideration of solution conditions.
• This work provides a framework for studying complex protein-DNA interactions using fluorescence spectroscopy.