1
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Fu X, Diao W, Luo Y, Liu Y, Wang Z. Theoretical Insight into the Fluorescence Spectral Tuning Mechanism: A Case Study of Flavin-Dependent Bacterial Luciferase. J Chem Theory Comput 2024; 20:8652-8664. [PMID: 39298275 DOI: 10.1021/acs.jctc.4c00950] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/21/2024]
Abstract
Bioluminescence of bacteria is widely applied in biological imaging, environmental toxicant detection, and many other situations. Understanding the spectral tuning mechanism not only helps explain the diversity of colors observed in nature but also provides principles for bioengineering new color variants for practical applications. In this study, time-dependent density functional theory (TD-DFT) and quantum mechanics and molecular mechanics (QM/MM) calculations have been employed to understand the fluorescence spectral tuning mechanism of bacterial luciferase with a focus on the electrostatic effect. The spectrum can be tuned by both a homogeneous dielectric environment and oriented external electric fields (OEEFs). Increasing the solvent polarity leads to a redshift of the fluorescence emission maximum, λF, accompanied by a substantial increase in density. In contrast, applying an OEEF along the long axis of the isoalloxazine ring (X-axis) leads to a significant red- or blue-shift in λF, depending on the direction of the OEEF, yet with much smaller changes in intensity. The effect of polar solvents is directionless, and the red-shifts can be attributed to the larger dipole moment of the S1 state compared with that of the S0 state. However, the effect of OEEFs directly correlates with the difference dipole moment between the S1 and S0 states, which is directional and is determined by the charge redistribution upon deexcitation. Moreover, the electrostatic effect of bacterial luciferase is in line with the presence of an internal electric field (IEF) pointing in the negative X direction. Finally, the key residues that contribute to this IEF and strategies for modulating the spectrum through site-directed point mutations are discussed.
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Affiliation(s)
- Xiaodi Fu
- Center for Advanced Materials Research, Beijing Normal University, Zhuhai 519087, China
| | - Wenwen Diao
- Oujiang Laboratory (Zhejiang Lab for Regenerative Medicine, Vision and Brain Health), Wenzhou 325000, China
| | - Yanling Luo
- School of Chinese Materia Medica, Tianjin University of Traditional Chinese Medicine, Tianjin 301617, China
| | - Yajun Liu
- Center for Advanced Materials Research, Beijing Normal University, Zhuhai 519087, China
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Zhanfeng Wang
- Center for Advanced Materials Research, Beijing Normal University, Zhuhai 519087, China
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2
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Pieri E, Walker AR, Zhu M, Martínez TJ. Conical Intersection Accessibility Dictates Brightness in Red Fluorescent Proteins. J Am Chem Soc 2024; 146:17646-17658. [PMID: 38885641 DOI: 10.1021/jacs.4c00458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/20/2024]
Abstract
Red fluorescent protein (RFP) variants are highly sought after for in vivo imaging since longer wavelengths improve depth and contrast in fluorescence imaging. However, the lower energy emission wavelength usually correlates with a lower fluorescent quantum yield compared to their green emitting counterparts. To guide the rational design of bright variants, we have theoretically assessed two variants (mScarlet and mRouge) which are reported to have very different brightness. Using an α-CASSCF QM/MM framework (chromophore and all protein residues within 6 Å of it in the QM region, for a total of more than 450 QM atoms), we identify key points on the ground and first excited state potential energy surfaces. The brighter variant mScarlet has a rigid scaffold, and the chromophore stays largely planar on the ground state. The dimmer variant mRouge shows more flexibility and can accommodate a pretwisted chromophore conformation which provides easier access to conical intersections. The main difference between the variants lies in the intersection seam regions, which appear largely inaccessible in mScarlet but partially accessible in mRouge. This observation is mainly related with changes in the cavity charge distribution, the hydrogen-bonding network involving the chromophore and a key ARG/THR mutation (which changes both charge and steric hindrance).
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Affiliation(s)
- Elisa Pieri
- Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, United States
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599, United States
| | - Alice R Walker
- Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, United States
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
- Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States
| | - Mingning Zhu
- Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, United States
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Todd J Martínez
- Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, United States
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
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3
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Tam C, Zhang KYJ. FPredX: Interpretable models for the prediction of spectral maxima, brightness, and oligomeric states of fluorescent proteins. Proteins 2021; 90:732-746. [PMID: 34676905 DOI: 10.1002/prot.26270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Revised: 09/19/2021] [Accepted: 10/15/2021] [Indexed: 11/06/2022]
Abstract
Fluorescent protein (FP) design is among the challenging protein design problems due to the tradeoffs among multiple properties to be optimized. Despite the accumulated efforts in design and characterization, progress has been slow in gaining a full understanding of sequence-property relationships to tackle the multiobjective design problem in FPs. In this study, we approach this problem by developing FPredX, a collection of gradient-boosted decision tree models, which mapped FP sequences to four major design targets of FPs, including excitation maximum, emission maximum, brightness, and oligomeric state. By training using one-hot encoded multiple aligned sequences with hyperparameters optimization in each model, FPredX models showed excellent prediction performance for all target properties compared with existing methods. We further interpreted the FPredX models by comparing the importance of positions along the aligned FP sequence to the predictive performance and suggested positions, which showed differential importance deemed by FPredX models to the prediction of each target property.
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Affiliation(s)
- Chunlai Tam
- Laboratory for Structural Bioinformatics, Center for Biosystems Dynamics Research, RIKEN, Yokohama, Japan.,Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Japan
| | - Kam Y J Zhang
- Laboratory for Structural Bioinformatics, Center for Biosystems Dynamics Research, RIKEN, Yokohama, Japan.,Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Japan
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4
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Rathnachalam S, Menger MFS, Faraji S. Influence of the Environment on Shaping the Absorption of Monomeric Infrared Fluorescent Proteins. J Phys Chem B 2021; 125:2231-2240. [PMID: 33626280 PMCID: PMC7957859 DOI: 10.1021/acs.jpcb.0c10466] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 01/25/2021] [Indexed: 12/05/2022]
Abstract
Infrared fluorescent proteins (iRFPs) are potential candidates for deep-tissue in vivo imaging. Here, we provide molecular-level insights into the role of the protein environment in the structural stability of the chromophore within the protein binding pocket through the flexible hydrogen-bonding network using molecular dynamics simulation. Furthermore, we present systematic excited-state analysis to characterize the nature of the first two excited states and the role of the environment in shaping the nature of the chromophore's excited states within the hybrid quantum mechanics/molecular mechanics framework. Our results reveal that the environment red-shifts the absorption of the chromophore by about 0.32 eV compared to the isolated counterpart, and besides the structural stability, the protein environment does not alter the nature of the excited state of the chromophore significantly. Our study contributes to the fundamental understanding of the excited-state processes of iRFPs in a complex environment and provides a design principle for developing iRFPs with desired spectral properties.
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Affiliation(s)
- Sivasudhan Rathnachalam
- Theoretical Chemistry
Group,
Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747AG, The Netherlands
| | - Maximilian F. S.
J. Menger
- Theoretical Chemistry
Group,
Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747AG, The Netherlands
| | - Shirin Faraji
- Theoretical Chemistry
Group,
Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747AG, The Netherlands
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5
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Cloin BMC, De Zitter E, Salas D, Gielen V, Folkers GE, Mikhaylova M, Bergeler M, Krajnik B, Harvey J, Hoogenraad CC, Van Meervelt L, Dedecker P, Kapitein LC. Efficient switching of mCherry fluorescence using chemical caging. Proc Natl Acad Sci U S A 2017; 114:7013-7018. [PMID: 28630286 PMCID: PMC5502588 DOI: 10.1073/pnas.1617280114] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Fluorophores with dynamic or controllable fluorescence emission have become essential tools for advanced imaging, such as superresolution imaging. These applications have driven the continuing development of photoactivatable or photoconvertible labels, including genetically encoded fluorescent proteins. These new probes work well but require the introduction of new labels that may interfere with the proper functioning of existing constructs and therefore require extensive functional characterization. In this work we show that the widely used red fluorescent protein mCherry can be brought to a purely chemically induced blue-fluorescent state by incubation with β-mercaptoethanol (βME). The molecules can be recovered to the red fluorescent state by washing out the βME or through irradiation with violet light, with up to 80% total recovery. We show that this can be used to perform single-molecule localization microscopy (SMLM) on cells expressing mCherry, which renders this approach applicable to a very wide range of existing constructs. We performed a detailed investigation of the mechanism underlying these dynamics, using X-ray crystallography, NMR spectroscopy, and ab initio quantum-mechanical calculations. We find that the βME-induced fluorescence quenching of mCherry occurs both via the direct addition of βME to the chromophore and through βME-mediated reduction of the chromophore. These results not only offer a strategy to expand SMLM imaging to a broad range of available biological models, but also present unique insights into the chemistry and functioning of a highly important class of fluorophores.
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Affiliation(s)
- Bas M C Cloin
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Elke De Zitter
- Biochemistry, Molecular and Structural Biology, Department of Chemistry, KU Leuven, 3001 Heverlee, Belgium
| | - Desiree Salas
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Vincent Gielen
- Biochemistry, Molecular and Structural Biology, Department of Chemistry, KU Leuven, 3001 Heverlee, Belgium
| | - Gert E Folkers
- NMR Spectroscopy, Department of Chemistry, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Marina Mikhaylova
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Maike Bergeler
- Quantum Chemistry and Physical Chemistry, Department of Chemistry, KU Leuven, 3001 Heverlee, Belgium
| | - Bartosz Krajnik
- Molecular Imaging and Photonics, Department of Chemistry, KU Leuven, 3001 Heverlee, Belgium
- Institute of Physics, Faculty of Physics, Astronomy, and Informatics, Nicolaus Copernicus University, 87-100 Torun, Poland
| | - Jeremy Harvey
- Quantum Chemistry and Physical Chemistry, Department of Chemistry, KU Leuven, 3001 Heverlee, Belgium
| | - Casper C Hoogenraad
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Luc Van Meervelt
- Biochemistry, Molecular and Structural Biology, Department of Chemistry, KU Leuven, 3001 Heverlee, Belgium
| | - Peter Dedecker
- Biochemistry, Molecular and Structural Biology, Department of Chemistry, KU Leuven, 3001 Heverlee, Belgium;
| | - Lukas C Kapitein
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands;
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6
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Acharya A, Bogdanov AM, Grigorenko BL, Bravaya KB, Nemukhin AV, Lukyanov KA, Krylov AI. Photoinduced Chemistry in Fluorescent Proteins: Curse or Blessing? Chem Rev 2016; 117:758-795. [PMID: 27754659 DOI: 10.1021/acs.chemrev.6b00238] [Citation(s) in RCA: 178] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Photoinduced reactions play an important role in the photocycle of fluorescent proteins from the green fluorescent protein (GFP) family. Among such processes are photoisomerization, photooxidation/photoreduction, breaking and making of covalent bonds, and excited-state proton transfer (ESPT). Many of these transformations are initiated by electron transfer (ET). The quantum yields of these processes vary significantly, from nearly 1 for ESPT to 10-4-10-6 for ET. Importantly, even when quantum yields are relatively small, at the conditions of repeated illumination the overall effect is significant. Depending on the task at hand, fluorescent protein photochemistry is regarded either as an asset facilitating new applications or as a nuisance leading to the loss of optical output. The phenomena arising due to phototransformations include (i) large Stokes shifts, (ii) photoconversions, photoactivation, and photoswitching, (iii) phototoxicity, (iv) blinking, (v) permanent bleaching, and (vi) formation of long-lived intermediates. The focus of this review is on the most recent experimental and theoretical work on photoinduced transformations in fluorescent proteins. We also provide an overview of the photophysics of fluorescent proteins, highlighting the interplay between photochemistry and other channels (fluorescence, radiationless relaxation, and intersystem crossing). The similarities and differences with photochemical processes in other biological systems and in dyes are also discussed.
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Affiliation(s)
- Atanu Acharya
- Department of Chemistry, University of Southern California , Los Angeles, California 90089-0482, United States
| | - Alexey M Bogdanov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Moscow, Russia.,Nizhny Novgorod State Medical Academy , Nizhny Novgorod, Russia
| | - Bella L Grigorenko
- Department of Chemistry, Lomonosov Moscow State University , Moscow, Russia.,Emanuel Institute of Biochemical Physics, Russian Academy of Sciences , Moscow, Russia
| | - Ksenia B Bravaya
- Department of Chemistry, Boston University , Boston, Massachusetts United States
| | - Alexander V Nemukhin
- Department of Chemistry, Lomonosov Moscow State University , Moscow, Russia.,Emanuel Institute of Biochemical Physics, Russian Academy of Sciences , Moscow, Russia
| | - Konstantin A Lukyanov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Moscow, Russia.,Nizhny Novgorod State Medical Academy , Nizhny Novgorod, Russia
| | - Anna I Krylov
- Department of Chemistry, University of Southern California , Los Angeles, California 90089-0482, United States
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7
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Faraji S, Krylov AI. On the Nature of an Extended Stokes Shift in the mPlum Fluorescent Protein. J Phys Chem B 2015; 119:13052-62. [PMID: 26402581 DOI: 10.1021/acs.jpcb.5b07724] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Far-red fluorescent proteins (FPs) enable deep-tissue in vivo imaging. Combining FPs with large and small Stokes shifts enables single-excitation/dual-emission multicolor applications. Using a quantum mechanics/molecular mechanics (QM/MM) scheme, we carried out a series of simulations to identify the origin of an extended Stokes shift (0.2 eV) observed in mPlum, one of the most far-red-shifted FPs. We demonstrated that the red shift of emission is largely due to the excited-state relaxation of the chromophore itself. Rigid protein environment suppresses the relaxation; however, if the hydrogen-bond network around the chromophore is sufficiently flexible, it can rearrange upon electronic excitation, allowing the chromophore to relax. The reorganization of the hydrogen-bond network is driven by changes in bonding and charge distributions of the chromophore in the excited state. The ILE65 and GLU16 residues play the most important role. The MD simulations reveal two ground-state populations with the direct (Chro-ILE65···GLU16) and water-mediated (Chro-ILE65···Wat321···GLU16) hydrogen-bond patterns. In the excited state, both populations relax to a single emitting state with the water-mediated (Chro-ILE65···Wat321···GLU16) hydrogen-bond pattern, which provides a better match for the excited-state charge distribution (the acylimine's oxygen has a larger negative charge in S1 than in S0). The extended Stokes shift arises due to the conversion of the direct hydrogen-bond pattern to the water-mediated one accompanied by large structural relaxation of the electronically excited chromophore. This conclusion is supported by calculations for the GLU16LEU mutant, which has only one hydrogen-bond pattern. Consequently, no interconversion is possible, and the computed Stokes shift is small, in agreement with the experiment. Our theoretical findings provide support to a recent study of the Stokes shifts in mPlum and its mutants.
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Affiliation(s)
- Shirin Faraji
- Department of Chemistry, University of Southern California , Los Angeles, California 90089-0482, United States
| | - Anna I Krylov
- Department of Chemistry, University of Southern California , Los Angeles, California 90089-0482, United States
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8
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Khrenova M, Topol I, Collins J, Nemukhin A. Estimating orientation factors in the FRET theory of fluorescent proteins: the TagRFP-KFP pair and beyond. Biophys J 2015; 108:126-32. [PMID: 25564859 PMCID: PMC4286598 DOI: 10.1016/j.bpj.2014.11.1859] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Revised: 10/20/2014] [Accepted: 11/06/2014] [Indexed: 11/29/2022] Open
Abstract
The orientation factor κ(2), one of the key parameters defining Förster resonance energy transfer efficiency, is determined by the transition dipole moment orientations of the donor and acceptor species. Using the results of quantum chemical and quantum mechanical/molecular mechanical calculations for the chromophore-containing pockets in selected colored proteins of the green fluorescent protein family, we derived transition dipole moments corresponding to the S0,min → S1 excitation for green fluorescent protein, red fluorescent protein (TagRFP), and kindling fluorescent protein, and the S1,min → S0 emission for TagRFP. These data allowed us to estimate κ(2) values for the TagRFP-linker-kindling fluorescent protein tetrameric complex required for constructing novel sensors.
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Affiliation(s)
- Maria Khrenova
- Department of Chemistry, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Igor Topol
- Advanced Biomedical Computing Center, Information Systems Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland.
| | - Jack Collins
- Advanced Biomedical Computing Center, Information Systems Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland
| | - Alexander Nemukhin
- Department of Chemistry, Lomonosov Moscow State University, Moscow, Russian Federation; Emanuel Institute of Biochemical Physics, Moscow, Russian Federation
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9
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Kang B, Baek KY, Lee JY. Electric Field Effect on trans-p-Hydroxybenzylideneimidazolidinone: A DFT Study and Implication to Green Fluorescent Protein. B KOREAN CHEM SOC 2015. [DOI: 10.1002/bkcs.10063] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Baotao Kang
- Department of Chemistry; Sungkyunkwan University; Suwon 440746 Korea
| | - Kyung Yup Baek
- Department of Chemistry; Sungkyunkwan University; Suwon 440746 Korea
| | - Jin Yong Lee
- Department of Chemistry; Sungkyunkwan University; Suwon 440746 Korea
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10
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Harczuk I, Murugan NA, Vahtras O, Ågren H. Studies of pH-Sensitive Optical Properties of the deGFP1 Green Fluorescent Protein Using a Unique Polarizable Force Field. J Chem Theory Comput 2014; 10:3492-502. [PMID: 26588314 DOI: 10.1021/ct5001318] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The aim of this study is to identify the responsible molecular forms for the pH dependent optical properties of the deGFP1 green fluorescent protein mutant. We have carried out static and dynamic type calculations for all four protonation states of the chromophore to unravel the contributions due to finite temperature and the flexible protein backbone on the pH dependent optical properties. In particular, we have used a combined molecular dynamics and density functional-molecular mechanics linear response approach by means of which the optical property calculations were carried out for the chromophore in the explicitly treated solvent and bioenvironment. Two different models were used to describe the environment-electronic embedding and polarizable electronic embedding-accounting for the polarization of the chromophore and the mutual polarization between the chromophore and the environment, respectively. For this purpose a polarizable force field was derived quantum mechanically for the protein environment by use of analytical response theory. While the gas-phase calculations for the chromophore predict that the induced red shift going from low to high pH is attributed to the change of molecular forms from neutral to zwitterionic, the two more advanced models that explicitly account for the protein backbone attribute the pH shift to a neutral to anionic conversion. Some ramifications of the results for the use of GFPs as pH sensors are discussed.
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Affiliation(s)
- I Harczuk
- Division of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology , S-106 91 Stockholm, Sweden
| | - N Arul Murugan
- Division of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology , S-106 91 Stockholm, Sweden
| | - O Vahtras
- Division of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology , S-106 91 Stockholm, Sweden
| | - H Ågren
- Division of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology , S-106 91 Stockholm, Sweden
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11
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Drobizhev M, Stoltzfus C, Topol I, Collins J, Wicks G, Mikhaylov A, Barnett L, Hughes T, Rebane A. Multiphoton photochemistry of red fluorescent proteins in solution and live cells. J Phys Chem B 2014; 118:9167-79. [PMID: 25004113 PMCID: PMC4126731 DOI: 10.1021/jp502477c] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Revised: 07/02/2014] [Indexed: 12/13/2022]
Abstract
Genetically encoded fluorescent proteins (FPs), and biosensors based on them, provide new insights into how living cells and tissues function. Ultimately, the goal of the bioimaging community is to use these probes deep in tissues and even in entire organisms, and this will require two-photon laser scanning microscopy (TPLSM), with its greater tissue penetration, lower autofluorescence background, and minimum photodamage in the out-of-focus volume. However, the extremely high instantaneous light intensities of femtosecond pulses in the focal volume dramatically increase the probability of further stepwise resonant photon absorption, leading to highly excited, ionizable and reactive states, often resulting in fast bleaching of fluorescent proteins in TPLSM. Here, we show that the femtosecond multiphoton excitation of red FPs (DsRed2 and mFruits), both in solution and live cells, results in a chain of consecutive, partially reversible reactions, with individual rates driven by a high-order (3-5 photon) absorption. The first step of this process corresponds to a three- (DsRed2) or four-photon (mFruits) induced fast isomerization of the chromophore, yielding intermediate fluorescent forms, which then subsequently transform into nonfluorescent products. Our experimental data and model calculations are consistent with a mechanism in which ultrafast electron transfer from the chromophore to a neighboring positively charged amino acid residue triggers the first step of multiphoton chromophore transformations in DsRed2 and mFruits, consisting of decarboxylation of a nearby deprotonated glutamic acid residue.
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Affiliation(s)
- Mikhail Drobizhev
- Department of Physics and Department of
Cell Biology and Neuroscience, Montana State
University, Bozeman, Montana 59717, United
States
| | - Caleb Stoltzfus
- Department of Physics and Department of
Cell Biology and Neuroscience, Montana State
University, Bozeman, Montana 59717, United
States
| | - Igor Topol
- Leidos
Biomedical Research, Inc., Frederick National Laboratory for Cancer
Research, Frederick, Maryland 21702-1201, United States
| | - Jack Collins
- Leidos
Biomedical Research, Inc., Frederick National Laboratory for Cancer
Research, Frederick, Maryland 21702-1201, United States
| | - Geoffrey Wicks
- Department of Physics and Department of
Cell Biology and Neuroscience, Montana State
University, Bozeman, Montana 59717, United
States
| | - Alexander Mikhaylov
- Department of Physics and Department of
Cell Biology and Neuroscience, Montana State
University, Bozeman, Montana 59717, United
States
| | - Lauren Barnett
- Department of Physics and Department of
Cell Biology and Neuroscience, Montana State
University, Bozeman, Montana 59717, United
States
| | - Thomas
E. Hughes
- Department of Physics and Department of
Cell Biology and Neuroscience, Montana State
University, Bozeman, Montana 59717, United
States
| | - Aleksander Rebane
- Department of Physics and Department of
Cell Biology and Neuroscience, Montana State
University, Bozeman, Montana 59717, United
States
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12
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Nachimuthu S, Lai KH, Taufany F, Jiang JC. Theoretical study on molecular design and optical properties of organic sensitizers. Phys Chem Chem Phys 2014; 16:15389-99. [PMID: 24946111 DOI: 10.1039/c4cp01653j] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
A series of organic sensitizers based on different configurations such as D-π-A, D-[π]n-A, D-π-[A]n, [D]n-π-A, D-π-A-π-D, D-π-[A]n-π-D and D-[π-A]n-π-D (where n = 1-4) are designed using theoretical methods. The effects of repeating π-linker, donor-acceptor moieties and the substitution of additional donor-acceptor moieties on the optoelectronic properties have been addressed. Our results show that the strength of the acceptor units changes the mono band absorption into dual band absorption in all the considered strategies. We found that repeating π-linker/donor moieties in the D-π-A series enhances the intensity of the absorption and can tune their absorption spectra from UV-to-visible and visible to near IR regions by repeating acceptor units. Also, the present results indicate that the D-π-A-π-D configuration shows improved optical properties than the conventional D-π-A structure. This theoretical study explores the new configurations and design strategies of organic dyes for developing efficient light harvesting devices working in the whole visible and near IR regions.
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Affiliation(s)
- Santhanamoorthi Nachimuthu
- Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei-106, Taiwan.
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13
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Konold P, Regmi CK, Chapagain PP, Gerstman BS, Jimenez R. Hydrogen bond flexibility correlates with Stokes shift in mPlum variants. J Phys Chem B 2014; 118:2940-8. [PMID: 24611679 DOI: 10.1021/jp412371y] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Fluorescent proteins have revolutionized molecular biology research and provide a means of tracking subcellular processes with extraordinary spatial and temporal precision. Species with emission beyond 650 nm offer the potential for deeper tissue penetration and lengthened imaging times; however, the origin of their extended Stokes shift is not fully understood. We employed spectrally resolved transient grating spectroscopy and molecular dynamics simulations to investigate the relationship between the flexibility of the chromophore environment and Stokes shift in mPlum. We examined excited state solvation dynamics in a panel of strategic point mutants of residues E16 and I65 proposed to participate in a hydrogen-bonding interaction thought responsible for its red-shifted emission. We observed two characteristic relaxation constants of a few picoseconds and tens of picoseconds that were assigned to survival times of direct and water-mediated hydrogen bonds at the 16-65 position. Moreover, variants of the largest Stokes shift (mPlum, I65V) exhibited significant decay on both time scales, indicating the bathochromic shift correlates with a facile switching between a direct and water-mediated hydrogen bond. This dynamic model underscores the role of environmental flexibility in the mechanism of excited state solvation and provides a template for engineering next-generation red fluorescent proteins.
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Affiliation(s)
- Patrick Konold
- JILA, University of Colorado and NIST , Boulder, Colorado 80309, United States
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Kang B, Liu H, Jang DJ, Lee JY. Electric field effect on the ground state proton transfer in the H-bonded HBDI complex: an implication of the green fluorescent protein. RSC Adv 2014. [DOI: 10.1039/c4ra00974f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
In this paper, first-principles calculations were performed regarding the electric field effect on the ground state proton transfer (GSPT) in the H-bonded p-hydroxybenzylideneimidazolidinone (HBDI) network that represents the active site of the green fluorescent protein (GFP).
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Affiliation(s)
- Baotao Kang
- Department of Chemistry
- Sungkyunkwan University
- Suwon, Korea
| | - Hongguang Liu
- Department of Chemistry
- Sungkyunkwan University
- Suwon, Korea
| | - Du-Jeon Jang
- Department of Chemistry
- Seoul National University
- Seoul 151-742, Korea
| | - Jin Yong Lee
- Department of Chemistry
- Sungkyunkwan University
- Suwon, Korea
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15
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Nadal-Ferret M, Gelabert R, Moreno M, Lluch JM. How Does the Environment Affect the Absorption Spectrum of the Fluorescent Protein mKeima? J Chem Theory Comput 2013; 9:1731-42. [DOI: 10.1021/ct301003t] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Marc Nadal-Ferret
- Departament
de Química and ‡Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Ricard Gelabert
- Departament
de Química and ‡Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Miquel Moreno
- Departament
de Química and ‡Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - José M. Lluch
- Departament
de Química and ‡Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
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16
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List NH, Olsen JMH, Jensen HJA, Steindal AH, Kongsted J. Molecular-Level Insight into the Spectral Tuning Mechanism of the DsRed Chromophore. J Phys Chem Lett 2012; 3:3513-3521. [PMID: 26290981 DOI: 10.1021/jz3014858] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We present a detailed study of the protein environmental effects on the one- and two-photon absorption (1PA and 2PA, respectively) properties of the S0-S1 transition in the DsRed protein using the polarizable embedding density functional theory formalism. We find that steric factors and chromophore-protein interactions act in concert to enhance the 2PA activity inside the protein while adversely blue-shifting the 1PA maximum. A two-state model reveals that the 2PA intensity gain is primarily governed by the increased change in the permanent dipole moment between the ground and the excited states acquired inside the protein. Our results indicate that this mainly is attributable to counter-directional contributions stemming from Lys163 and the conserved Arg95 with the former additionally identified as a key residue in the color tuning mechanism. The results provide new insight into the tuning mechanism of DsRed and suggest a possible strategy for simultaneous improvement of its 1PA and 2PA properties.
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Affiliation(s)
- Nanna H List
- †Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Jógvan Magnus H Olsen
- †Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Hans Jørgen Aa Jensen
- †Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Arnfinn H Steindal
- ‡Centre of Theoretical and Computational Chemistry, Department of Chemistry, N-9037 Tromsø, Norway
| | - Jacob Kongsted
- †Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense M, Denmark
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17
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Affiliation(s)
- Fedor V. Subach
- Department of Anatomy and Structural Biology, and Gruss-Lipper Biophotonics Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Vladislav V. Verkhusha
- Department of Anatomy and Structural Biology, and Gruss-Lipper Biophotonics Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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18
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Bravaya KB, Grigorenko BL, Nemukhin AV, Krylov AI. Quantum chemistry behind bioimaging: insights from ab initio studies of fluorescent proteins and their chromophores. Acc Chem Res 2012; 45:265-75. [PMID: 21882809 DOI: 10.1021/ar2001556] [Citation(s) in RCA: 116] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The unique properties of green fluorescent protein (GFP) have been harnessed in a variety of bioimaging techniques, revolutionizing many areas of the life sciences. Molecular-level understanding of the underlying photophysics provides an advantage in the design of new fluorescent proteins (FPs) with improved properties; however, because of its complexity, many aspects of the GFP photocycle remain unknown. In this Account, we discuss computational studies of FPs and their chromophores that provide qualitative insights into mechanistic details of their photocycle and the structural basis for their optical properties. In a reductionist framework, studies of well-defined model systems (such as isolated chromophores) help to understand their intrinsic properties, while calculations including protein matrix and/or solvent demonstrate, on the atomic level, how these properties are modulated by the environment. An interesting feature of several anionic FP chromophores in the gas phase is their low electron detachment energy. For example, the bright excited ππ* state of the model GFP chromophore (2.6 eV) lies above the electron detachment continuum (2.5 eV). Thus, the excited state is metastable with respect to electron detachment. This autoionizing character needs to be taken into account in interpreting gas-phase measurements and is very difficult to describe computationally. Solvation (and even microsolvation by a single water molecule) stabilizes the anionic states enough such that the resonance excited state becomes bound. However, even in stabilizing environments (such as protein or solution), the anionic chromophores have relatively low oxidation potentials and can act as light-induced electron donors. Protein appears to affect excitation energies very little (<0.1 eV), but alters ionization or electron detachment energies by several electron volts. Solvents (especially polar ones) have a pronounced effect on the chromophore's electronic states; for example, the absorption wavelength changes considerably, the ground-state barrier for cis-trans isomerization is reduced, and fluorescence quantum yield drops dramatically. Calculations reveal that these effects can be explained in terms of electrostatic interactions and polarization, as well as specific interactions such as hydrogen bonding. The availability of efficient computer implementations of predictive electronic structure methods is essential. Important challenges include developing faster codes (to enable better equilibrium sampling and excited-state dynamics modeling), creating algorithms for properties calculations (such as nonlinear optical properties), extending standard excited-state methods to autoionizing (resonance) states, and developing accurate QM/MM schemes. The results of sophisticated first-principle calculations can be interpreted in terms of simpler, qualitative molecular orbital models to explain general trends. In particular, an essential feature of the anionic GFP chromophore is an almost perfect resonance (mesomeric) interaction between two Lewis structures, giving rise to charge delocalization, bond-order scrambling, and, most importantly, allylic frontier molecular orbitals spanning the methine bridge. We demonstrate that a three-center Hückel-like model provides a useful framework for understanding properties of FPs. It can explain changes in absorption wavelength upon protonation or other structural modifications of the chromophore, the magnitude of transition dipole moment, barriers to isomerization, and even non-Condon effects in one- and two-photon absorption.
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Affiliation(s)
- Ksenia B. Bravaya
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | - Bella L. Grigorenko
- Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow 119991, Russia
| | - Alexander V. Nemukhin
- Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow 119991, Russia
- N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow 119334, Russia
| | - Anna I. Krylov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
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19
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Topol I, Collins J, Nemukhin A. Modeling Structures and Spectra of Fluorescent Proteins in the Coordinate-Locking Cluster Approach: Application to the Photoswitchable Protein AsFP595. ACTA ACUST UNITED AC 2012. [DOI: 10.4236/cmb.2012.23008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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