A conserved interaction with the chromophore of fluorescent proteins

Protein Sci. 2012 Feb;21(2):171-7. doi: 10.1002/pro.762. Epub 2011 Dec 21.


The chromophore of fluorescent proteins, including the green fluorescent protein (GFP), contains a highly conjugated imidazolidinone ring. In many fluorescent proteins, the carbonyl group of the imidazolidinone ring engages in a hydrogen bond with the side chain of an arginine residue. Prior studies have indicated that such an electrophilic carbonyl group in a protein often accepts electron density from a main-chain oxygen. A survey of high-resolution structures of fluorescent proteins indicates that electron lone pairs of a main-chain oxygen-Thr62 in GFP-donate electron density into an antibonding orbital of the imidazolidinone carbonyl group. This n→π* electron delocalization prevents structural distortion during chromophore excitation that could otherwise lead to fluorescence quenching. In addition, this interaction is present in on-pathway intermediates leading to the chromophore, and thus could direct its biogenesis. Accordingly, this n→π* interaction merits inclusion in computational and photophysical analyses of the chromophore, and in speculations about the molecular evolution of fluorescent proteins.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Catalytic Domain / genetics
  • Chromogenic Compounds / chemistry
  • Chromogenic Compounds / metabolism*
  • Conserved Sequence* / physiology
  • Fluorescence
  • Green Fluorescent Proteins / chemistry
  • Green Fluorescent Proteins / metabolism
  • Hydrogen Bonding
  • Imidazolidines / chemistry
  • Imidazolidines / metabolism
  • Luminescent Proteins / chemistry*
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism*
  • Models, Biological
  • Models, Molecular
  • Protein Binding / genetics
  • Protein Binding / physiology
  • Protein Interaction Domains and Motifs* / genetics


  • Chromogenic Compounds
  • Imidazolidines
  • Luminescent Proteins
  • Green Fluorescent Proteins