Dual-Mode FRET and BRET Sensors for Detecting cAMP Dynamics

Genetically encoded fluorescent and luminescent indicators have revolutionized our ability to monitor physiology in real time, but the separate development of new sensors for each of these imaging modalities involves substantial effort and resources. Methods to rapidly engineer multimodal sensors would, therefore, significantly accelerate the diversification of sensors for simultaneous use in different systems and applications. We hypothesized that the enhanced Nano-lanterns could be incorporated into modular ratiometric sensors as an efficient approach to creating dual-mode fluorescent-luminescent sensors. As a proof-of-concept, we engineered an Epac1-based sensor that responds to cyclic adenosine monophosphate binding with a greater than 80% change in both Förster Resonance Energy Transfer and bioluminescent resonance energy transfer (BRET) modes. We also demonstrate that our new sensor reports cellular changes in G-protein-coupled signaling, and that the ratiometric BRET mode is bright enough for subcutaneous measurements in mice.