FRET and TR-FRET Assays

Principle

FRET is a proximity-based assay that detects energy transfer between a donor fluorophore and an acceptor when they are within 1–10 nm. The energy transfer occurs when two labeled proteins come into close proximity, generating a detectable fluorescent signal.

Cellular Applications

FRET is widely used in cell-based studies to observe protein-protein interactions, conformational changes, and signaling events in real time. It is suitable for monitoring dynamic cellular processes and the spatial distribution of molecules.

Advancement of FRET

TR-FRET improves upon traditional FRET by introducing a lanthanide-based donor with a long fluorescence lifetime, such as europium or terbium. This substantially reduces background from nonspecific short-lived fluorescence.

Principle

After a defined time delay following excitation, fluorescence from the donor and acceptor is measured. Time-resolved detection enables more sensitive analysis in cell-based assays.

Applications in Cells

TR-FRET is particularly effective for high-throughput screening in drug discovery, including studies of GPCR signaling and kinase interactions where background noise in standard FRET assays may obscure weak signals.

Refinement of TR-FRET

HTRF is a commercialized form of TR-FRET that combines time-resolved fluorescence with ratiometric detection, providing robust and reproducible measurements.

Principle

In HTRF, donor molecules such as europium cryptate and acceptor molecules such as XL665 generate a measurable ratiometric signal that reflects the molecular interaction under study.

Applications

HTRF is widely used in drug discovery for receptor-ligand binding assays, protein interaction studies, and intracellular signaling analysis. Its robustness makes it suitable for large-scale cell-based assays and quantitative PPI analysis.