Subach, O.M. et al. J. Am. Chem. Soc. 134, 14789–14799 (2012).
Photoswitchable fluorescent proteins (PSFPs) are widely used for tracking intracellular proteins or cells, and they are important probes for super-resolution microscopy. Most PSFPs change from emitting green to red fluorescence upon irradiation with phototoxic violet light; but recently a fluorescent protein (PSmOrange) was developed that can be photoswitched with visible light from orange to far red, which represents the most red-shifted excitation peak of all GFP-like fluorescent proteins. Building on that work, Subach et al. now report a new version of PSmOrange with ninefold higher photoconversion contrast and tenfold faster photoswitching kinetics. PSmOrange2 can be efficiently photoswitched with common two-photon lasers and via fluorescence resonance energy transfer (FRET) from green fluorescent donors—an effect that the authors call 'FRET-facilitated photoswitching' and that they demonstrate using several sets of interacting proteins.
