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Lolli G, Raboni S, Pasqualetto E, Benoni R, Campanini B, Ronda L, Mozzarelli A, Bettati S, Battistutta R. Insight into GFPmut2 pH Dependence by Single Crystal Microspectrophotometry and X-ray Crystallography. J Phys Chem B 2018; 122:11326-11337. [PMID: 30179482 DOI: 10.1021/acs.jpcb.8b07260] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The fluorescence of Green Fluorescent Protein (wtGFP) and variants has been exploited in distinct applications in cellular and analytical biology. GFPs emission depends on the population of the protonated (A-state) and deprotonated (B-state) forms of the chromophore. Whereas wtGFP is pH-independent, mutants in which Ser65 is replaced by either threonine or alanine (as in GFPmut2) are pH-dependent, with a p Ka around 6. Given the wtGFP pH-independence, only the structure of the protonated form was determined. The deprotonated form was deduced on the basis of the crystal structure of the Ser65Thr mutant at basic pH, assuming that it corresponds to the conformation populated in solution. Here, we present an investigation where structures of the protonated and deprotonated forms of GFPmut2 were determined from crystals grown in either MPD at pH 6 or PEG at pH 8.5, and moved to either higher or lower pH. Both crystal forms of GFPmut2 were titrated monitoring the process via polarized absorption microspectrophotometry in order to precisely correlate the protonation process with the structures. We found that (i) in solution, chromophore titration is not thermodynamically coupled with any residue and Glu222 is always protonated independent of the protonation state of the chromophore; (ii) the lack of coupling is reflected in the structural behavior of the chromophore and Glu222 environments, with only the former showing variations with pH; (iii) titrations of low-pH and high-pH grown crystals exhibit a Hill coefficient of about 0.75, indicating an anticooperative behavior not observed in solution; (iv) structures where pH was changed in the crystal point to Glu222 as the ionizable group responsible for the outset of the anticooperative behavior; and (v) in GFPmut2 the canonical GFP proton wire involving the chromophore is not interrupted at the level of Ser205 and Glu222 at basic pH as in the Ser65Thr mutant. This allows proposing the structure of the deprotonated state of GFPmut2 as an alternative model for the analogous state of wtGFP.
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Affiliation(s)
- Graziano Lolli
- Centro di Biologia Integrata - CIBIO , Università di Trento , 38123 Povo , Trento , Italy
| | - Samanta Raboni
- Dipartimento di Scienze degli Alimenti e del Farmaco , Università di Parma , 43124 Parma , Italy
| | - Elisa Pasqualetto
- Dipartimento di Scienze Chimiche , Università degli Studi di Padova and Istituto di Chimica Biomolecolare, Consiglio Nazionale delle Ricerche , 35131 Padua , Italy
| | - Roberto Benoni
- Dipartimento di Medicina e Chirurgia , Università di Parma , 43125 Parma , Italy
| | - Barbara Campanini
- Dipartimento di Scienze degli Alimenti e del Farmaco , Università di Parma , 43124 Parma , Italy
| | - Luca Ronda
- Dipartimento di Medicina e Chirurgia , Università di Parma , 43125 Parma , Italy
| | - Andrea Mozzarelli
- Dipartimento di Scienze degli Alimenti e del Farmaco , Università di Parma , 43124 Parma , Italy.,Istituto di Biofisica , Consiglio Nazionale delle Ricerche , 56124 Pisa , Italy.,Istituto Nazionale Biostrutture e Biosistemi , 00136 Rome , Italy
| | - Stefano Bettati
- Dipartimento di Medicina e Chirurgia , Università di Parma , 43125 Parma , Italy.,Istituto Nazionale Biostrutture e Biosistemi , 00136 Rome , Italy
| | - Roberto Battistutta
- Dipartimento di Scienze Chimiche , Università degli Studi di Padova and Istituto di Chimica Biomolecolare, Consiglio Nazionale delle Ricerche , 35131 Padua , Italy
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Vegh RB, Bloch DA, Bommarius AS, Verkhovsky M, Pletnev S, Iwaï H, Bochenkova AV, Solntsev KM. Hidden photoinduced reactivity of the blue fluorescent protein mKalama1. Phys Chem Chem Phys 2015; 17:12472-85. [DOI: 10.1039/c5cp00887e] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
We report a complete photocycle of the blue fluorescent protein exhibiting two delayed branches coupled to hidden proton transfer events.
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Affiliation(s)
- Russell B. Vegh
- School of Chemistry and Biochemistry
- Georgia Institute of Technology
- Atlanta
- USA
- Petit Institute of Bioengineering and Bioscience
| | - Dmitry A. Bloch
- Research Program in Structural Biology and Biophysics
- Institute of Biotechnology
- University of Helsinki
- Helsinki 00014
- Finland
| | - Andreas S. Bommarius
- School of Chemistry and Biochemistry
- Georgia Institute of Technology
- Atlanta
- USA
- Petit Institute of Bioengineering and Bioscience
| | - Michael Verkhovsky
- Research Program in Structural Biology and Biophysics
- Institute of Biotechnology
- University of Helsinki
- Helsinki 00014
- Finland
| | - Sergei Pletnev
- Synchrotron Radiation Research Section
- Macromolecular Crystallography Laboratory
- National Cancer Institute
- Argonne
- USA
| | - Hideo Iwaï
- Research Program in Structural Biology and Biophysics
- Institute of Biotechnology
- University of Helsinki
- Helsinki 00014
- Finland
| | | | - Kyril M. Solntsev
- School of Chemistry and Biochemistry
- Georgia Institute of Technology
- Atlanta
- USA
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Auerbach D, Klein M, Franz S, Carius Y, Lancaster CRD, Jung G. Replacement of Highly Conserved E222 by the Photostable Non-photoconvertible Histidine in GFP. Chembiochem 2014; 15:1404-8. [DOI: 10.1002/cbic.201402075] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Indexed: 11/12/2022]
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Jablonski AE, Vegh RB, Hsiang JC, Bommarius B, Chen YC, Solntsev KM, Bommarius AS, Tolbert LM, Dickson RM. Optically modulatable blue fluorescent proteins. J Am Chem Soc 2013; 135:16410-7. [PMID: 24099419 DOI: 10.1021/ja405459b] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Blue fluorescent proteins (BFPs) offer visualization of protein location and behavior, but often suffer from high autofluorescent background and poor signal discrimination. Through dual-laser excitation of bright and photoinduced dark states, mutations to the residues surrounding the BFP chromophore enable long-wavelength optical modulation of BFP emission. Such dark state engineering enables violet-excited blue emission to be increased upon lower energy, green coillumination. Turning this green coillumination on and off at a specific frequency dynamically modulates collected blue fluorescence without generating additional background. Interpreted as transient photoconversion between neutral cis and anionic trans chromophoric forms, mutations tune photoisomerization and ground state tautomerizations to enable long-wavelength depopulation of the millisecond-lived, spectrally shifted dark states. Single mutations to the tyrosine-based blue fluorescent protein T203V/S205V exhibit enhanced modulation depth and varied frequency. Importantly, analogous single point mutations in the nonmodulatable BFP, mKalama1, creates a modulatable variant. Building modulatable BFPs offers opportunities for improved BFP signal discrimination vs background, greatly enhancing their utility.
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Affiliation(s)
- Amy E Jablonski
- School of Chemistry and Biochemistry, ‡School of Chemical and Biomolecular Engineering, and §Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States
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Jablonski AE, Hsiang JC, Bagchi P, Hull N, Richards CI, Fahrni CJ, Dickson RM. Signal Discrimination Between Fluorescent Proteins in Live Cells by Long-wavelength Optical Modulation. J Phys Chem Lett 2012; 3:3585-3591. [PMID: 23419973 PMCID: PMC3570161 DOI: 10.1021/jz3016414] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Fluorescent proteins (FPs) have revolutionized molecular and cellular biology; yet, discrimination over cellular autofluorescence, spectral deconvolution, or detection at low concentrations remain challenging problems in many biological applications. By optically depopulating a photoinduced dark state with orange secondary laser co-excitation, the higher-energy green AcGFP fluorescence is dynamically increased. Modulating this secondary laser then modulates the higher-energy, collected fluorescence; enabling its selective detection by removing heterogeneous background from other FPs. Order-of-magnitude reduction in obscuring fluorophore background emission has been achieved in both fixed and live cells. This longwavelength modulation expands the dimensionality to discriminate FP emitters based on dark state lifetimes and enables signal of interest to be recovered by removing heterogeneous background emitter signals. Thus, AcGFP is not only useful for extracting weak signals from systems plagued by high background, but it is a springboard for further FP optimization and utilization for improving sensitivity and selectivity in biological fluorescence imaging.
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Daglio SC, Banterle N, D’Alfonso L, Collini M, Chirico G. Diffusion–Photodynamics Coupling in Fluorescence Correlation Spectroscopy Studies of Photoswitchable Green Fluorescent Proteins: An Analytical and Simulative Study. J Phys Chem B 2011; 115:10311-21. [DOI: 10.1021/jp205147n] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- S. C. Daglio
- Dipartimento di Fisica, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, I-20126, Milano, Italy
| | - N. Banterle
- Dipartimento di Fisica, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, I-20126, Milano, Italy
| | - L. D’Alfonso
- Dipartimento di Fisica, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, I-20126, Milano, Italy
| | - M. Collini
- Dipartimento di Fisica, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, I-20126, Milano, Italy
| | - G. Chirico
- Dipartimento di Fisica, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, I-20126, Milano, Italy
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Bettati S, Pasqualetto E, Lolli G, Campanini B, Battistutta R. Structure and single crystal spectroscopy of Green Fluorescent Proteins. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1814:824-33. [PMID: 20940063 DOI: 10.1016/j.bbapap.2010.10.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2010] [Revised: 10/01/2010] [Accepted: 10/04/2010] [Indexed: 11/15/2022]
Abstract
Usually, spectroscopic data on proteins in solution are interpreted at molecular level on the basis of the three-dimensional structures determined in the crystalline state. While it is widely recognized that the protein crystal structures are reliable models for the solution 3D structures, nevertheless it is also clear that sometimes the crystallization process can introduce some "artifacts" that can make difficult or even flaw the attempt to correlate the properties in solution with those in the crystalline state. In general, therefore, it would be desirable to identify some sort of control. In the case of the spectroscopic properties of proteins, the most straightforward check is to acquire data not only in solution but also on the crystals. In this regard, the Green Fluorescent Protein (GFP) is an interesting case in that a massive quantity of data correlating the spectroscopic properties in solution with the structural information in the crystalline state is available in literature. Despite that, a relatively limited amount of spectroscopic studies on single crystals of GFP or related FPs have been described. Here we review and discuss the main spectroscopic (in solution) and structural (in crystals) studies performed on the GFP and related fluorescent proteins, together with the spectroscopic analyses on various FPs members in the crystalline state. One main conclusion is that "in cristallo" spectroscopic studies are useful in providing new opportunities for gathering information not available in solution and are highly recommended to reliably correlate solution properties with structural features. This article is part of a Special Issue entitled: Protein Structure and Function in the Crystalline State.
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Affiliation(s)
- Stefano Bettati
- Department of Biochemistry and Molecular Biology, University of Parma, Viale Usberti 23/A, 43124 Parma, Italy
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Jiménez-Banzo A, Ragàs X, Abbruzzetti S, Viappiani C, Campanini B, Flors C, Nonell S. Singlet oxygen photosensitisation by GFP mutants: oxygen accessibility to the chromophore. Photochem Photobiol Sci 2010; 9:1336-41. [DOI: 10.1039/c0pp00125b] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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