Spectroscopy and microscopy of the autofluorescent protein DsRed from Discosoma genus coral

We report on the fluorescence dynamics of a red fluorescent protein DsRed from the coral Discosoma genus by means of ensemble and single molecule fluorescence spectroscopy. Single molecule experiments performed on 543-nm excitation point to the existence of DsRed as a tetramer and reveal the presence of a no/off blinking phenomenon in the millisecond time range. Collective effects involving the red chromophores within the individual tetramers were observed. Time-resolved fluorescence data reveal the presence of a population of 25 % of the immature green chromophores which relates to tetramers containing only this immature green form and which is responsible for the weak fluorescence emitted by DsRed at 500-nm when excited at 460-nm. The remaining 75 % of the immature green chromophores are involved in a FRET process to the red chromophores within the tetramers that contain them. Using time-resolved detection and spectroscopy at single molecule level we were able to demonstrate the presence of a photoconversion process of the red chromophore emitting at 583-nm into a super red species that emits weakly at 595-nm. The same phenomenon is further corroborated at the ensemble level with the observation of the creation of a super red form and a blue absorbing species upon irradiation with 532-nm pulsed light at high excitation power.