Engineering of a monomeric green-to-red photoactivatable fluorescent protein induced by blue light

Green fluorescent protein (GFP) and GFP-like proteins represent invaluable genetically encoded fluorescent probes(1,2). In the last few years a new class of photoactivatable fluorescent proteins (PAFPs) capable of pronounced light-induced spectral changes have been developed(3). Except for tetrameric KFP1 (ref. 4), all known PAFPs, including PA-GFP(5), Kaede(6), EosFP(7), PS-CFP8, Dronpa(9), PA-mRFP1(10) and KikGR(11) require light in the UV-violet spectral region for activation through one-photon excitation-such light can be phototoxic to some biological systems(12). Here, we report a monomeric PAFP, Dendra, derived from octocoral Dendronephthya sp. and capable of 1,000- to 4,500- fold photoconversion from green to red fluorescent states in response to either visible blue or UV-violet light. Dendra represents the first PAFP, which is simultaneously monomeric, efficiently matures at 37 degrees C, demonstrates high photostability of the activated state, and can be photoactivated by a common, marginally phototoxic, 488-nm laser line. We demonstrate the suitability of Dendra for protein labeling and tracking to quantitatively study dynamics of fibrillarin and vimentin in mammalian cells.