Intensity correlation-based calibration of FRET

Area of Science:

• Biophysics
• Cell Biology
• Analytical Chemistry

Background:

• Flow cytometric resonance energy transfer (FCET) is vital for studying molecular proximity in living cells.
• Accurate determination of the scaling factor (α) is critical for quantifying fluorescence resonance energy transfer (FRET) efficiency.
• Existing methods for determining α are complex, requiring special samples or advanced statistical procedures.

Purpose of the Study:

• To present a novel, spectral-constants-free method for determining the scaling factor (α) and absolute FRET efficiency.
• To enhance the FCET algorithm by incorporating analysis of intensity distribution moments (variances and covariances).
• To validate the robustness and accuracy of the new method across various experimental conditions.

Main Methods:

• Developed an extended FCET algorithm analyzing second moments (variances and covariances) of intensity distributions.
• Formulated a quadratic equation for α based on intensity fluctuations.
• Applied the method to measure FRET between MHCI receptor epitopes on FT and LS174T cell lines.

Main Results:

• The new method accurately determines α and FRET efficiency on a cell-by-cell basis.
• It overcomes limitations of traditional methods, particularly at high dye-per-protein labeling ratios.
• The approach demonstrates robustness across a wide range of conditions.

Conclusions:

• The novel approach provides a more accessible and robust way to quantify molecular proximity using FCET.
• It simplifies the determination of α, making FRET analysis more widely applicable.
• The method is transferable to other fluorescence-based imaging techniques, including fluorescence microscopy.