Fluorescent Cassettes for Monitoring Three-Component Interactions in Vitro and in Living Cells

Fluorescence resonance energy transfer (FRET) is a key tech-nique for monitoring protein-protein interactions.1,2 However, a restriction of FRET is that the fluorescence emission of the donor must overlap with the absorption of the acceptor. This limits the spectral output dispersion that can be achieved using a single donor and a set of acceptors. To address this issue, our group has been involved in the design and syntheses of “through-bond energy transfer (TBET) cassettes ” in which a donor relays energy to an acceptor predominantly via twisted π-electron systems.3,4 A major obstacle, however, has been syntheses of water-soluble TBET-cassettes that efficiently relay energy to the acceptor and emit it as fluorescence in aqueous environments. This communication de-scribes cassettes 1 and 2 (Figure 1a) that have good spectral properties in this regard and their application to observe protein-protein interactions in Vitro and in living cells