7o7u
Crystal structure of rsEGFP2 in the non-fluorescent off-state determined by serial femtosecond crystallography at room temperature
Structural highlights
FunctionGFP_AEQVI Energy-transfer acceptor. Its role is to transduce the blue chemiluminescence of the protein aequorin into green fluorescent light by energy transfer. Fluoresces in vivo upon receiving energy from the Ca(2+)-activated photoprotein aequorin. Publication Abstract from PubMedReversibly photoswitchable fluorescent proteins are essential markers for advanced biological imaging, and optimization of their photophysical properties underlies improved performance and novel applications. Here we establish a link between photoswitching contrast, one of the key parameters that dictate the achievable resolution in nanoscopy applications, and chromophore conformation in the non-fluorescent state of rsEGFP2, a widely employed label in REversible Saturable OpticaL Fluorescence Transitions (RESOLFT) microscopy. Upon illumination, the cis chromophore of rsEGFP2 isomerizes to two distinct off-state conformations, trans1 and trans2, located on either side of the V151 side chain. Reducing or enlarging the side chain at this position (V151A and V151L variants) leads to single off-state conformations that exhibit higher and lower switching contrast, respectively, compared to the rsEGFP2 parent. The combination of structural information obtained by serial femtosecond crystallography with high-level quantum chemical calculations and with spectroscopic and photophysical data determined in vitro suggests that the changes in switching contrast arise from blue- and red-shifts of the absorption bands associated to trans1 and trans2, respectively. Thus, due to elimination of trans2, the V151A variants of rsEGFP2 and its superfolding variant rsFolder2 display a more than two-fold higher switching contrast than their respective parent proteins, both in vitro and in E. coli cells. The application of the rsFolder2-V151A variant is demonstrated in RESOLFT nanoscopy. Our study rationalizes the connection between structural and photophysical chromophore properties and suggests a means to rationally improve fluorescent proteins for nanoscopy applications. Rational Control of Off-State Heterogeneity in a Photoswitchable Fluorescent Protein Provides Switching Contrast Enhancement.,Adam V, Hadjidemetriou K, Jensen N, Shoeman RL, Woodhouse J, Aquila A, Banneville AS, Barends TRM, Bezchastnov V, Boutet S, Byrdin M, Cammarata M, Carbajo S, Eleni Christou N, Coquelle N, De la Mora E, El Khatib M, Moreno Chicano T, Bruce Doak R, Fieschi F, Foucar L, Glushonkov O, Gorel A, Grunbein ML, Hilpert M, Hunter M, Kloos M, Koglin JE, Lane TJ, Liang M, Mantovanelli A, Nass K, Nass Kovacs G, Owada S, Roome CM, Schiro G, Seaberg M, Stricker M, Thepaut M, Tono K, Ueda K, Uriarte LM, You D, Zala N, Domratcheva T, Jakobs S, Sliwa M, Schlichting I, Colletier JP, Bourgeois D, Weik M Chemphyschem. 2022 Aug 12:e202200192. doi: 10.1002/cphc.202200192. PMID:35959919[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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