Biochemistry 1997 Aug 12;36(32):9759-9765

Crystal structure and photodynamic behavior of the blue
emission variant Y66H/Y145F of green fluorescent protein.

Wachter RM, King BA, Heim R, Kallio K, Tsien RY, Boxer SG, Remington SJ

Institute of Molecular Biology, Department of Physics, University of Oregon, Eugene 97403,
USA.                

The crystal structure of a blue emission variant (Y66H/Y145F) of the Aequorea victoria green
fluorescent protein has been determined by molecular replacement and the model refined. The
crystallographic R-factor is 18.1% for all data from 20 to 2.1 A, and the model geometry is
excellent. The chromophore is non-native and is autocatalytically generated from the internal
tripeptide Ser65-His66-Gly67. The final electron density maps indicate that the formation of the
chromophore is complete, including 1,2 dehydration of His66 as indicated by the planarity of the
chromophore. The chromophore is in the cis conformation, with no evidence for any substantial
fraction of the trans configuration or uncyclized apoprotein, and is well-shielded from bulk
solvent by the folded protein. These characteristics indicate that the machinery for production of
the chromophore from a buried tripeptide unit is not only intact but also highly efficient in spite
of a major change in chromophore chemical structure. Nevertheless, there are significant
rearrangements in the hydrogen bond configuration around the chromophore as compared to
wild-type, indicating flexibility of the active site. pH titration of the intact protein and the
chromopeptide (pKa1 = 4.9 +/- 0.1, pKa2 = 12.0 +/- 0.1) suggests that the predominant form of
the chromophore in the intact protein is electrically neutral. In contrast to the wild-type protein
[Chattoraj, M., King, B. A., Bublitz, G. U., & Boxer, S. G. (1996) Proc. Natl. Acad. Sci. U.S.A.,
8362-8367], femtosecond fluorescence up-conversion spectroscopy of the intact protein and a
partially deuterated form strongly suggests that excited-state proton transfer is not coupled to
fluorescence emission.

PMID: 9245407, UI: 97392641