Photophysics and high-resolution spectroscopy of green fluorescent protein

Abstract

The green fluorescent protein (GFP) has recently attracted great attention because it is the only cloned protein that exhibits strong fluorescence without any extraneous chromophores [1]. When fused to other proteins, it becomes a marker for gene expression and allows visualization of dynamic events inside living cells [2, 3]. Although the crystal structure of GFP has been solved [4], its photophysical properties remained puzzling. It was known that wild-type GFP in the ground state can exist in two forms, A (neutral) and B (anionic), and it was suggested [5] that a photoconversion from A to B involves an excited-state proton transfer, while an intermediate I-form, not identified in the spectra, was held responsible for the green fluorescence observed at 508 nm.