Environment-sensitive labels in multiplex fluorescence analyses of protein-DNA complexes

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Fluorescein is a common protein label due to its optical properties.
• Fluorescein's fluorescence is sensitive to quenching, a property exploitable for quantitative assays.
• Understanding heat shock transcription factor (HSF) self-association and DNA binding is crucial for gene regulation studies.

Purpose of the Study:

• To develop a quantitative method using fluorescein-labeled HSF to study protein self-association.
• To determine the stoichiometry of HSF in complexes with specific DNA using fluorescence.
• To leverage fluorescein's quenching properties for accurate biomolecular interaction analysis.

Main Methods:

• A fluorescein-labeled HSF construct (HSFDT385-Fl) was created by conjugating fluorescein 5-maleimide to a HSF fragment containing DNA-binding and trimerization domains.
• Protein trimerization equilibrium constants were determined by monitoring fluorescence changes upon titration with unlabeled HSF.
• Two-color fluorescence emission assays with energy transfer-labeled DNA were used to quantify protein and DNA in gel-shifted complexes.

Main Results:

• The equilibrium constant for HSF trimerization was estimated to be 3 x 10(-16) M2.
• HSFDT385-Fl fluorescence increased 1.7-fold upon binding to specific DNA, but not nonspecific DNA.
• Accurate determination of protein and DNA content in gel-shifted complexes was achieved using a two-color fluorescence assay.

Conclusions:

• Fluorescein labeling provides a sensitive method for studying HSF self-association and DNA binding.
• The developed fluorescence assay accurately quantifies protein and DNA in protein-DNA complexes.
• This approach offers a valuable tool for investigating the molecular mechanisms of transcription factors.