2Q57

X-ray structure of Cerulean GFP: A tryptophan-based chromophore useful for fluorescence lifetime imaging

Summary for 2Q57

• Entry DOI: 10.2210/pdb2q57/pdb
• Descriptor: Cerulean Green fluorescent protein (2 entities in total)
• Functional Keywords: beta barrel, fluorescent protein
• Biological source: Aequorea victoria
• Total number of polymer chains: 1
• Total formula weight: 28703.44

Authors

Malo, G.D. (deposition date: 2007-05-31, release date: 2007-11-27, Last modification date: 2024-10-16)

Primary citation

Malo, G.D.,Pouwels, L.J.,Wang, M.,Weichsel, A.,Montfort, W.R.,Rizzo, M.A.,Piston, D.W.,Wachter, R.M.
X-ray structure of Cerulean GFP: a tryptophan-based chromophore useful for fluorescence lifetime imaging.
Biochemistry, 46:9865-9873, 2007

PubMed Abstract: The crystal structure of the cyan-fluorescent Cerulean green fluorescent protein (GFP), a variant of enhanced cyan fluorescent protein (ECFP), has been determined to 2.0 A. Cerulean bears an internal fluorophore composed of an indole moiety derived from Y66W, conjugated to the GFP-like imidazolinone ring via a methylene bridge. Cerulean undergoes highly efficient fluorescence resonance energy transfer (FRET) to yellow acceptor molecules and exhibits significantly reduced excited-state heterogeneity. This feature was rationally engineered in ECFP by substituting His148 with an aspartic acid [Rizzo et al. (2004) Nat. Biotechnol. 22, 445], rendering Cerulean useful for fluorescence lifetime imaging microscopy (FLIM). The X-ray structure is consistent with a single conformation of the chromophore and surrounding residues and may therefore provide a structural rationale for the previously described monoexponential fluorescence decay. Unexpectedly, the carboxyl group of H148D is found in a buried position, directly contacting the indole nitrogen of the chromophore via a bifurcated hydrogen bond. Compared to the similarly constructed ECFP chromophore, the indole group of Cerulean is rotated around the methylene bridge to adopt a cis-coplanar conformation with respect to the imidazolinone ring, resulting in a close edge-to-edge contact of the two ring systems. The double-humped absorbance spectrum persists in single-crystal absorbance measurements, casting doubt on the idea that ground state conformational heterogeneity forms the basis of the two overlapping transitions. At low pH, a blue shift in absorbance of 10-15 nm suggests a pH-induced structural transition that proceeds with a time constant of 47 (+/-2) min and is reversible. Possible interpretations in terms of chromophore isomerization are presented.

PubMed: 17685554
DOI: 10.1021/bi602664c

Experimental method

X-RAY DIFFRACTION (2 Å)