Rosy dawn for fluorescent proteins (original) (raw)

Nature Biotechnology volume 17, pages 956–957 (1999)Cite this article

Green Fluorescent Protein (GFP) from the jellyfish Aequorea is the first protein discovered to possess intrinsic bright visible fluorescence. It converts the blue emission of the chemiluminescent protein aequorin into the green light emitted by the intact jellyfish. In the few years since its gene was cloned, GFP has become an indispensable tool for biologists and a fascinating puzzle for spectroscopists (see ref. 1 for a review). But Aequorea GFP is not the only fluorescent protein (FP) in nature, so what about exploiting some of the others? Until now the search for proteins with intrinsic visible fluorescence has focused on other bioluminescent organisms, such as the sea pens Renilla and Ptilosarcu . Although GFPs have been cloned from these species2, their sequences have not been disclosed and their emission wavelengths do not expand the palette of blue to yellowish green already available from mutants of Aequorea GFP. Unrelated FPs such as the phycobiliproteins, the antenna proteins in cyanobacteria, use small-molecule pigments as their chromophores3. For such FPs to be visible after heterologous expression, either their cofactors would either have to be supplied exogenously and successfully incorporated into the apoprotein, or else the genes encoding their entire biosynthetic pathway would have to be transferred.

An interesting puzzle is how to explain red emissions peaking at wavelengths as long as 583 nm—54 nm beyond the longest-wavelength mutant of Aequorea GFP. Matz and coworkers4 reasonably propose that a further post-translational reaction may have extended the π-conjugated system. One might add two more speculations: perhaps the chromophore's carbonyl becomes linked with an amine side chain to form an iminium cation, analogous to the reaction of retinal with Lys296 in rhodopsin. The 583 nm-emitting fluorophore may also share structural features with the mysterious red-fluorescent species formed from many Aequorea GFPs upon strong illumination under anaerobic conditions9,10. This red fluorescence has been attributed to porphyrin contamination in GFP-expressing cells11, but this explanation cannot be the whole story because the reddish fluorescence can also be generated from purified protein9, even in frozen solutions (L. Gross & R.Y. Tsien, unpublished observations). Perhaps the coral has learned how to make a similar modification without the need for illumination and exclusion of oxygen. Answers to these questions await a high-resolution structure of the red FP.

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Figure 1: (A) View of the Discosoma sp. coral (center) from which the red-emitting fluorescent protein was isolated.

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Authors and Affiliations

  1. the Howard Hughes Medical Institute and Department of Pharmacology, University of California, San Diego , 92093-0647, CA
    Roger Y. Tsien

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Tsien, R. Rosy dawn for fluorescent proteins.Nat Biotechnol 17, 956–957 (1999). https://doi.org/10.1038/13648

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