Imaging FRET standards by steady-state fluorescence and lifetime methods

Area of Science:

• Biophysics
• Molecular Biology
• Cellular Imaging

Background:

• Fluorescence Resonance Energy Transfer (FRET) imaging is vital for studying molecular dynamics in live cells.
• Quantifying FRET efficiency is challenging due to variations in methods and instrumentation, hindering data comparability.
• Standardized FRET probes are needed to ensure reliable and reproducible measurements across different laboratories.

Purpose of the Study:

• To construct and systematically evaluate novel FRET standard probes with varying efficiencies.
• To assess the performance of these FRET standards across multiple quantification techniques.
• To validate the utility of FRET standards for accurate molecular interaction studies in cellular environments.

Main Methods:

• Development of intramolecular FRET standards using protein fusions (ECFP/citrine) and a tetracysteine-FlAsH system.
• Inclusion of intermolecular FRET controls for comprehensive evaluation.
• Comparison of FRET standards using four quantification methods: emission ratioing, acceptor photobleaching, spectral unmixing, and fluorescence lifetime imaging (FLIM).

Main Results:

• FRET standards with varying efficiencies were successfully constructed and evaluated.
• Consistent FRET rates/indexes were obtained across different quantification methods, demonstrating probe reliability.
• Minor discrepancies noted for the CFP-tetraCys/FlAsH pair between CFP quenching and FLIM measurements.

Conclusions:

• The developed FRET standard probes provide a reliable tool for calibrating and validating FRET measurements.
• These standards facilitate accurate and comparable studies of molecular interactions in cellular systems.
• Standardization of FRET techniques through reliable probes enhances the robustness of live-cell imaging studies.