Photo-induced peptide cleavage in the green-to-red conversion of a fluorescent protein.
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.
Mizuno
Hideaki
H
Laboratory for Cell Function Dynamics, Advanced Technology Development Group, Brain Science Institute, The Institute of Physical and Chemical Science (RIKEN), 2-1 Hirosawa, Wako-city, Saitama 351-0198, Japan.
Mal
Tapas Kumar
TK
Tong
Kit I
KI
Ando
Ryoko
R
Furuta
Toshiaki
T
Ikura
Mitsuhiko
M
Miyawaki
Atsushi
A
D037421:Anthozoa / Q000737:chemistry; D006868:Hydrolysis / Q000528:radiation effects; D008164:Luminescent Proteins / Q000737:chemistry* / Q000528:radiation effects*; D008968:Molecular Conformation / Q000528:radiation effects; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry* / Q000528:radiation effects*; D010777:Photochemistry; D011499:Protein Processing, Post-Translational; D014466:Ultraviolet Rays
D008164:Luminescent Proteins; D010455:Peptides