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Publication Abstract from PubMed

Enhanced Cyan Fluorescent Protein (ECFP) and its variant Cerulean are genetically-encoded fluorophores widely used as donors in FRET-based cell imaging experiments. First, we have confirmed through denaturation experiments that the double-peak spectroscopic signature of these fluorescent proteins originates from the indole ring of the chromophore. Then, to explain the improvement in the fluorescence properties of Cerulean when compared to ECFP, we have determined the high-resolution crystal structures of these two proteins at physiological pH, and performed molecular dynamics simulations. In both proteins, the N-terminal half of the seventh strand exhibits two conformations that have a complex set of van der Waals interactions with the chromophore and that our simulations suggest interconvert on the nanosecond timescale. The Y145A and H148D mutations in Cerulean stabilize these interactions and allow the chromophore to be more planar, better stabilized and less prone to collisional quenching, albeit only intermittently. As a consequence, the probability of non-radiative decay is significantly decreased. Our results highlight the considerable dynamical flexibility that exists in the vicinity of the tryptophan-based chromophore of these engineered fluorescent proteins, and provide insights which should allow the design of mutants with enhanced optical properties.

Intrinsic dynamics in ECFP and Cerulean control fluorescence quantum yield.,Lelimousin M, Noirclerc-Savoye M, Lazareno-Saez C, Paetzold B, Le Vot S, Chazal R, Macheboeuf P, Field MJ, Bourgeois D, Royant A Biochemistry. 2009 Sep 15. PMID:19754158^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.