The structural basis for red fluorescence in the tetrameric GFP homolog DsRed

Green fluorescent protein (GFP) has rapidly become a standard tool far inve stigating a variety of cellular activities, and has served as a model syste m for understanding spectral tuning in chromophoric proteins. Distant homol ogs of GFP in reef coral and anemone display two new properties of the fluo rescent protein family: dramatically red-shifted spectra, and oligomerizati on to form tetramers. We now report the 1.9 Angstrom crystal structure of D sRed, a red fluorescent protein from Discosoma coral. DsRed monomers show s imilar topology to GFP, but additional chemical modification to the chromop hore extends the conjugated pi -system and likely accounts for the red-shif ted spectra. Oligomerization of DsRed occurs at two chemically distinct pro tein interfaces to assemble the tetramer. The DsRed structure reveals the c hemical basis for the functional properties of red fluorescent proteins and provides the basis for rational engineering of this subfamily of GFP homol ogs.