The 2.1 Å 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: Elsevier Ltd 27.05.2005
• Subjects: chromophore configuration; fluorescent protein; HcRed; structure; GFP; fluorescent protein; BSA; HcRed; CPs; FPs; vdw; chromophore configuration; structure
• ISSN: 0022-2836; 1089-8638
• 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 2.1 Å 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 β-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.