Light-induced conformational changes and energy transfer in red fluorescent protein

Reversible conformational changes have been photo-induced in the red fluorescent protein DsRed at low temperature by wavelength-selective laser irradiation. We have found two new fluorescent forms: a shifted-red (SR-) and a new green (G0-) form that absorb and emit, respectively, B14 nm to the red and B80 nm to the blue of the ‘mature’ red (R-) form present in an un-illuminated sample of DsRed. Further, we have identified the 0–0 transitions of the various forms by spectral hole burning and estimated their ground-state energy differences and barrier heights by means of temperaturedependent excitation and fluorescence spectroscopy between 1.6 and 295K. We have also proven that ‘downhill’ energy transfer takes place between these forms within the tetrameric structure of DsRed. r 2004 Elsevier B.V. All rights reserved.