Photoinduced activation of GFP-like proteins in tissues of reef corals

A variety of fluorescent and chromophoric proteins homologous to the green fluorescent protein (GFP) has been recently discovered and cloned from non-bioluminescent marine animals, such as corals, and now provide a multitude of colors for use in fluorescence imaging applications. Recently, a novel fluorescence imaging methodology has emerged that utilizes the unique photoactivatory property of several GFP-like proteins, which respond to irradiation by altering their optical properties, thereby providing a new spatio-temporal capability to the GFP-based imaging applications. During our studies of GFP-like proteins from the Great Barrier Reef corals, several novel photoactivatable (PA) GFP-like proteins have been discovered. These include fluorescence photo-amplifiers and reversible photoswitchers, similar to PA jelly-fish derived PA-GFP and Dronpa, that greatly increase their emissions following ultraviolet-A (UVA) irradiation; the red-to-green (R-to-G) converters, similar to DsRed, that rapidly change to green color following single- or 2-photon irradiation; the green-to-red (G-to-R) converters, that acquire bright red fluorescence following UV-violet irradiation, similar to Kaede-like proteins; and the kindling GFP-like proteins, that are non fluorescent, but rapidly acquire bright fluorescence after green light irradiation. We report on the various optical characteristics of these coral PA proteins that may be used to expand the scope of the available fluorescence bio-imaging technologies.