Photo-induced peptide cleavage in the green-to-red conversion of a fluorescent protein

Mol Cell. 2003 Oct;12(4):1051-8. doi: 10.1016/s1097-2765(03)00393-9.


Green fluorescent protein from the jellyfish (Aequorea GFP) and GFP-like proteins from coral species encode light-absorbing chromophores within their protein sequences. A coral fluorescent protein, Kaede, contains a tripeptide, His(62)-Tyr(63)-Gly(64), which acts as a green chromophore that is photoconverted to red. Here, we present the structural basis for the green-to-red photoconversion. As in Aequorea GFP, a chromophore, 4-(p-hydroxybenzylidene)-5-imidazolinone, derived from the tripeptide mediates green fluorescence in Kaede. UV irradiation causes an unconventional cleavage within Kaede protein between the amide nitrogen and the alpha carbon (Calpha) at His(62) via a formal beta-elimination reaction, which requires the whole, intact protein for its catalysis. The subsequent formation of a double bond between His(62)-Calpha and -Cbeta extends the pi-conjugation to the imidazole ring of His(62), creating a new red-emitting chromophore, 2-[(1E)-2-(5-imidazolyl)ethenyl]-4-(p-hydroxybenzylidene)-5-imidazolinone. The present study not only reveals diversity in the chemical structure of fluorescent proteins but also adds a new dimension to posttranslational modification mechanisms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anthozoa / chemistry
  • Hydrolysis / radiation effects
  • Luminescent Proteins / chemistry*
  • Luminescent Proteins / radiation effects*
  • Molecular Conformation / radiation effects
  • Molecular Structure
  • Peptides / chemistry*
  • Peptides / radiation effects*
  • Photochemistry
  • Protein Processing, Post-Translational
  • Ultraviolet Rays*


  • Luminescent Proteins
  • Peptides