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

J Mol Biol. 2005 May 27;349(1):223-37. doi: 10.1016/j.jmb.2005.03.020. Epub 2005 Mar 22.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Luminescent Proteins / chemistry*
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism
  • Protein Structure, Tertiary
  • Sea Anemones / genetics
  • Sea Anemones / metabolism*
  • Structural Homology, Protein


  • Luminescent Proteins
  • red fluorescent protein

Associated data

  • PDB/1YZW