The 2.1A crystal structure of the far-red fluorescent protein HcRed: inherent conformational flexibility of the chromophore

• Published in: Journal of molecular biology Vol. 349; no. 1; pp. 223 - 237
• Main Authors: Wilmann, Pascal G, Petersen, Jan, Pettikiriarachchi, Anne, Buckle, Ashley M, Smith, Sean C, Olsen, Seth, Perugini, Matthew A, Devenish, Rodney J, Prescott, Mark, Rossjohn, Jamie
• Format: Journal Article
• Language: English
• Published: Netherlands 27.05.2005
• Subjects: Animals; Luminescent Proteins - chemistry; Luminescent Proteins - genetics; Luminescent Proteins - metabolism; Protein Structure, Tertiary; Red Fluorescent Protein; Sea Anemones - genetics; Sea Anemones - metabolism; Structural Homology, Protein
• ISSN: 0022-2836
• DOI: 10.1016/j.jmb.2005.03.020

We have determined the crystal structure of HcRed, a far-red fluorescent protein isolated from Heteractis crispa, to 2.1A resolution. HcRed was observed to form a dimer, in contrast to the monomeric form of green fluorescent protein (GFP) or the tetrameric forms of the GFP-like proteins (eqFP611, Rtms5 and DsRed). Unlike the well-defined chromophore conformation observed in GFP and the GFP-like proteins, the HcRed chromophore was observed to be considerably mobile. Within the HcRed structure, the cyclic tripeptide chromophore, Glu(64)-Tyr(65)-Gly(66), was observed to adopt both a cis coplanar and a trans non-coplanar conformation. As a result of these two conformations, the hydroxyphenyl moiety of the chromophore makes distinct interactions within the interior of the beta-can. These data together with a quantum chemical model of the chromophore, suggest the cis coplanar conformation to be consistent with the fluorescent properties of HcRed, and the trans non-coplanar conformation to be consistent with non-fluorescent properties of hcCP, the chromoprotein parent of HcRed. Moreover, within the GFP-like family, it appears that where conformational freedom is permissible then flexibility in the chromophore conformation is possible.