title: Crystallographic evidence for water-assisted photo-induced peptide cleavage in the stony coral fluorescent protein Kaede.
abstract: A coral fluorescent protein from Trachyphyllia geoffroyi, Kaede, possesses a tripeptide of His62-Tyr63-Gly64, which forms a chromophore with green fluorescence. This chromophore's fluorescence turns red following UV light irradiation. We have previously shown that such photoconversion is achieved by a formal beta-elimination reaction, which results in a cleavage of the peptide bond found between the amide nitrogen and the alpha-carbon at His62. However, the stereochemical arrangement of the chromophore and the precise structural basis for this reaction mechanism previously remained unknown. Here, we report the crystal structures of the green and red form of Kaede at 1.4 A and 1.6 A resolutions, respectively. Our structures depict the cleaved peptide bond in the red form. The chromophore conformations both in the green and red forms are similar, except a well-defined water molecule in the proximity of the His62 imidazole ring in the green form. We propose a molecular mechanism for green-to-red photoconversion, which is assisted by the water molecule.
authors: Division of Signaling Biology, Ontario Cancer Institute and Department of Medical Biophysics, 101 College St., Toronto, Ontario, M5G 1L7, Canada.
authors: Ikuko
authors: I
authors: Hayashi
authors: Laboratory for Cell Function and Dynamics, Advanced Technology Development Group, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako-city, Saitama, 351-0198, Japan.
authors: Hideaki
authors: H
authors: Mizuno
authors: Division of Signaling Biology, Ontario Cancer Institute and Department of Medical Biophysics, 101 College St., Toronto, Ontario, M5G 1L7, Canada.
authors: Kit I
authors: KI
authors: Tong
authors: Department of Biomolecular Science and Research Center for Advanced Materials with Integrated Properties, Toho University, 2-2-1 Miyama, Funabashi, Chiba, 274-8510, Japan.
authors: Toshiaki
authors: T
authors: Furuta
authors: Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors: Fujie
authors: F
authors: Tanaka
authors: Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors: Masato
authors: M
authors: Yoshimura
authors: Laboratory for Cell Function and Dynamics, Advanced Technology Development Group, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako-city, Saitama, 351-0198, Japan.
authors: Atsushi
authors: A
authors: Miyawaki
authors: Division of Signaling Biology, Ontario Cancer Institute and Department of Medical Biophysics, 101 College St., Toronto, Ontario, M5G 1L7, Canada. Electronic address: mikura@uhnres.utoronto.ca.
authors: Mitsuhiko
authors: M
authors: Ikura
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000737:chemistry*; D018360:Crystallography, X-Ray; D049452:Green Fluorescent Proteins / Q000737:chemistry / Q000378:metabolism; D008027:Light; D008164:Luminescent Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D010777:Photochemistry; D020836:Protein Structure, Quaternary; D014867:Water / Q000737:chemistry*
chemical_list: C513582:Kaede protein, Trachyphyllia geoffroyi; D008164:Luminescent Proteins; D010455:Peptides; D014867:Water; D049452:Green Fluorescent Proteins