2q57
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(New page: 200px<br /><applet load="2q57" size="350" color="white" frame="true" align="right" spinBox="true" caption="2q57, resolution 2.00Å" /> '''X-ray structure of C...)
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Revision as of 09:59, 23 January 2008
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X-ray structure of Cerulean GFP: A tryptophan-based chromophore useful for fluorescence lifetime imaging
Overview
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.
About this Structure
2Q57 is a Single protein structure of sequence from Aequorea victoria. Full crystallographic information is available from OCA.
Reference
X-ray structure of Cerulean GFP: a tryptophan-based chromophore useful for fluorescence lifetime imaging., Malo GD, Pouwels LJ, Wang M, Weichsel A, Montfort WR, Rizzo MA, Piston DW, Wachter RM, Biochemistry. 2007 Sep 4;46(35):9865-73. Epub 2007 Aug 8. PMID:17685554
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