1
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Bagheri N, Chen H, Rabasovic M, Widengren J. Non-fluorescent transient states of tyrosine as a basis for label-free protein conformation and interaction studies. Sci Rep 2024; 14:6464. [PMID: 38499633 PMCID: PMC10948778 DOI: 10.1038/s41598-024-57054-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Accepted: 03/13/2024] [Indexed: 03/20/2024] Open
Abstract
The amino acids tryptophan, tyrosine, and phenylalanine have been extensively used for different label-free protein studies, based on the intensity, lifetime, wavelength and/or polarization of their emitted fluorescence. Similar to most fluorescent organic molecules, these amino acids can undergo transitions into dark meta-stable states, such as triplet and photo-radical states. On the one hand, these transitions limit the fluorescence signal, but they are also highly environment-sensitive and can offer an additional set of parameters, reflecting interactions, folding states, and immediate environments around the proteins. In this work, by analyzing the average intensity of tyrosine emission under different excitation modulations with the transient state monitoring (TRAST) technique, we explored the photo physics of tyrosine as a basis for such environment-sensitive readouts. From how the dark state transitions of tyrosine varied with excitation intensity and solvent conditions we first established a photophysical model for tyrosine. Next, we studied Calmodulin (containing two tyrosines), and how its conformation is changed upon calcium binding. From these TRAST experiments, performed with 280 nm time-modulated excitation, we show that tyrosine dark state transitions clearly change with the calmodulin conformation, and may thus represent a useful source of information for (label-free) analyses of protein conformations and interactions.
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Affiliation(s)
- Niusha Bagheri
- Experimental Biomolecular Physics, Department of Applied Physics, Royal Institute of Technology (KTH), Albanova University Center, 106 91, Stockholm, Sweden
| | - Hongjian Chen
- Experimental Biomolecular Physics, Department of Applied Physics, Royal Institute of Technology (KTH), Albanova University Center, 106 91, Stockholm, Sweden
| | - Mihailo Rabasovic
- Laboratory for Biophysics, Institute of Physics Belgrade, Pregrevica 118, 11080, Zemun-Belgrade, Serbia
| | - Jerker Widengren
- Experimental Biomolecular Physics, Department of Applied Physics, Royal Institute of Technology (KTH), Albanova University Center, 106 91, Stockholm, Sweden.
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2
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Kang XW, Wang K, Zhang X, Zhong D, Ding B. Elementary Reactions in the Functional Triads of the Blue-Light Photoreceptor BLUF Domain. J Phys Chem B 2024; 128:2065-2075. [PMID: 38391132 DOI: 10.1021/acs.jpcb.3c07988] [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: 02/24/2024]
Abstract
The blue light using the flavin (BLUF) domain is one of the smallest photoreceptors in nature, which consists of a unique bidirectional electron-coupled proton relay process in its photoactivation reaction cycle. This perspective summarizes our recent efforts in dissecting the photocycle into three elementary processes, including proton-coupled electron transfer (PCET), proton rocking, and proton relay. Using ultrafast spectroscopy, we have determined the temporal sequence, rates, kinetic isotope effects (KIEs), and concertedness of these elementary steps. Our findings provide important implications for illuminating the photoactivation mechanism of the BLUF domain and suggest an engineering platform to characterize intricate reactions involving proton motions that are ubiquitous in nonphotosensitive protein machines.
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Affiliation(s)
- Xiu-Wen Kang
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Kailin Wang
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Xiaofan Zhang
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Dongping Zhong
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
- Department of Physics, Department of Chemistry and Biochemistry, and Programs of Biophysics, Programs of Chemical Physics, and Programs of Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Bei Ding
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
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3
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Tolentino Collado J, Bodis E, Pasitka J, Szucs M, Fekete Z, Kis-Bicskei N, Telek E, Pozsonyi K, Kapetanaki SM, Greetham G, Tonge PJ, Meech SR, Lukacs A. Single Amino Acid Mutation Decouples Photochemistry of the BLUF Domain from the Enzymatic Function of OaPAC and Drives the Enzyme to a Switched-on State. J Mol Biol 2024; 436:168312. [PMID: 37827329 DOI: 10.1016/j.jmb.2023.168312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 09/29/2023] [Accepted: 10/05/2023] [Indexed: 10/14/2023]
Abstract
Photoactivated adenylate cyclases (PACs) are light-activated enzymes that combine a BLUF (blue-light using flavin) domain and an adenylate cyclase domain that are able to increase the levels of the important second messenger cAMP (cyclic adenosine monophosphate) upon blue-light excitation. The light-induced changes in the BLUF domain are transduced to the adenylate cyclase domain via a mechanism that has not yet been established. One critical residue in the photoactivation mechanism of BLUF domains, present in the vicinity of the flavin is the glutamine amino acid close to the N5 of the flavin. The role of this residue has been investigated extensively both experimentally and theoretically. However, its role in the activity of the photoactivated adenylate cyclase, OaPAC has never been addressed. In this work, we applied ultrafast transient visible and infrared spectroscopies to study the photochemistry of the Q48E OaPAC mutant. This mutation altered the primary electron transfer process and switched the enzyme into a permanent 'on' state, able to increase the cAMP levels under dark conditions compared to the cAMP levels of the dark-adapted state of the wild-type OaPAC. Differential scanning calorimetry measurements point to a less compact structure for the Q48E OaPAC mutant. The ensemble of these findings provide insight into the important elements in PACs and how their fine tuning may help in the design of optogenetic devices.
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Affiliation(s)
| | - Emoke Bodis
- Department of Biophysics, Medical School, University of Pecs, Szigeti str. 12, 7624 Pecs, Hungary
| | - Jonatan Pasitka
- Department of Biophysics, Medical School, University of Pecs, Szigeti str. 12, 7624 Pecs, Hungary
| | - Mihaly Szucs
- Department of Biophysics, Medical School, University of Pecs, Szigeti str. 12, 7624 Pecs, Hungary
| | - Zsuzsanna Fekete
- Department of Biophysics, Medical School, University of Pecs, Szigeti str. 12, 7624 Pecs, Hungary
| | - Nikolett Kis-Bicskei
- Department of Biophysics, Medical School, University of Pecs, Szigeti str. 12, 7624 Pecs, Hungary
| | - Elek Telek
- Department of Biophysics, Medical School, University of Pecs, Szigeti str. 12, 7624 Pecs, Hungary
| | - Kinga Pozsonyi
- Department of Biophysics, Medical School, University of Pecs, Szigeti str. 12, 7624 Pecs, Hungary
| | - Sofia M Kapetanaki
- Department of Biophysics, Medical School, University of Pecs, Szigeti str. 12, 7624 Pecs, Hungary
| | - Greg Greetham
- Central Laser Facility, Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot OX11 0QX, UK
| | - Peter J Tonge
- Department of Chemistry, Stony Brook University, New York 11794, United States.
| | - Stephen R Meech
- School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK.
| | - Andras Lukacs
- Department of Biophysics, Medical School, University of Pecs, Szigeti str. 12, 7624 Pecs, Hungary.
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4
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Zhou Y, Tang S, Chen Z, Zhou Z, Huang J, Kang XW, Zou S, Wang B, Zhang T, Ding B, Zhong D. Origin of the multi-phasic quenching dynamics in the BLUF domains across the species. Nat Commun 2024; 15:623. [PMID: 38245518 PMCID: PMC10799861 DOI: 10.1038/s41467-023-44565-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Accepted: 12/19/2023] [Indexed: 01/22/2024] Open
Abstract
Blue light using flavin (BLUF) photoreceptors respond to light via one of nature's smallest photo-switching domains. Upon photo-activation, the flavin cofactor in the BLUF domain exhibits multi-phasic dynamics, quenched by a proton-coupled electron transfer reaction involving the conserved Tyr and Gln. The dynamic behavior varies drastically across different species, the origin of which remains controversial. Here, we incorporate site-specific fluorinated Trp into three BLUF proteins, i.e., AppA, OaPAC and SyPixD, and characterize the percentages for the Wout, WinNHin and WinNHout conformations using 19F nuclear magnetic resonance spectroscopy. Using femtosecond spectroscopy, we identify that one key WinNHin conformation can introduce a branching one-step proton transfer in AppA and a two-step proton transfer in OaPAC and SyPixD. Correlating the flavin quenching dynamics with the active-site structural heterogeneity, we conclude that the quenching rate is determined by the percentage of WinNHin, which encodes a Tyr-Gln configuration that is not conducive to proton transfer.
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Affiliation(s)
- Yalin Zhou
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Siwei Tang
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Zijing Chen
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Zhongneng Zhou
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Jiulong Huang
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Xiu-Wen Kang
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Shuhua Zou
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Bingyao Wang
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Tianyi Zhang
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Bei Ding
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China.
| | - Dongping Zhong
- Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China.
- Department of Physics, Department of Chemistry and Biochemistry, and Programs of Biophysics, Chemical Physics, and Biochemistry, The Ohio State University, Columbus, OH, 43210, USA.
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5
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Gibbs CA, Ghazi N, Tao J, Warren JJ. An Investigation of the Influence of Tyrosine Local Interactions on Electron Hopping in a Model Protein. Molecules 2024; 29:350. [PMID: 38257263 PMCID: PMC10818705 DOI: 10.3390/molecules29020350] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 01/04/2024] [Accepted: 01/05/2024] [Indexed: 01/24/2024] Open
Abstract
Multi-step electron transfer reactions are important to the function of many cellular systems. The ways in which such systems have evolved to direct electrons along specific pathways are largely understood, but less so are the ways in which the reduction-oxidation potentials of individual redox sites are controlled. We prepared a series of three new artificial variants of Pseudomonas aeruginosa azurin where a tyrosine (Tyr109) is situated between the native Cu ion and a Ru(II) photosensitizer tethered to a histidine (His107). Arginine, glutamine, or methionine were introduced as position 122, which is near to Tyr109. We investigated the rate of CuI oxidation by a flash-quench generated Ru(III) oxidant over pH values from 5 to 9. While the identity of the residue at position 122 affects some of the physical properties of Tyr109, the rates of CuI oxidation are only weakly dependent on the identity of the residue at 122. The results highlight that more work is still needed to understand how non-covalent interactions of redox active groups are affected in redox proteins.
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Affiliation(s)
| | | | | | - Jeffrey J. Warren
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
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6
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Tolentino Collado J, Iuliano JN, Pirisi K, Jewlikar S, Adamczyk K, Greetham GM, Towrie M, Tame JRH, Meech SR, Tonge PJ, Lukacs A. Unraveling the Photoactivation Mechanism of a Light-Activated Adenylyl Cyclase Using Ultrafast Spectroscopy Coupled with Unnatural Amino Acid Mutagenesis. ACS Chem Biol 2022; 17:2643-2654. [PMID: 36038143 PMCID: PMC9486806 DOI: 10.1021/acschembio.2c00575] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The hydrogen bonding network that surrounds the flavin in blue light using flavin adenine dinucleotide (BLUF) photoreceptors plays a crucial role in sensing and communicating the changes in the electronic structure of the flavin to the protein matrix upon light absorption. Using time-resolved infrared spectroscopy (TRIR) and unnatural amino acid incorporation, we investigated the photoactivation mechanism and the role of the conserved tyrosine (Y6) in the forward reaction of the photoactivated adenylyl cyclase from Oscillatoria acuminata (OaPAC). Our work elucidates the direct connection between BLUF photoactivation and the structural and functional implications on the partner protein for the first time. The TRIR results demonstrate the formation of the neutral flavin radical as an intermediate species on the photoactivation pathway which decays to form the signaling state. Using fluorotyrosine analogues to modulate the physical properties of Y6, the TRIR data reveal that a change in the pKa and/or reduction potential of Y6 has a profound effect on the forward reaction, consistent with a mechanism involving proton transfer or proton-coupled electron transfer from Y6 to the electronically excited FAD. Decreasing the pKa from 9.9 to <7.2 and/or increasing the reduction potential by 200 mV of Y6 prevents proton transfer to the flavin and halts the photocycle at FAD•-. The lack of protonation of the anionic flavin radical can be directly linked to photoactivation of the adenylyl cyclase (AC) domain. While the 3F-Y6 and 2,3-F2Y6 variants undergo the complete photocycle and catalyze the conversion of ATP into cAMP, enzyme activity is abolished in the 3,5-F2Y6 and 2,3,5-F3Y6 variants where the photocycle is halted at FAD•-. Our results thus show that proton transfer plays an essential role in initiating the structural reorganization of the AC domain that results in AC activity.
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Affiliation(s)
| | - James N. Iuliano
- Department
of Chemistry, Stony Brook University, New York, New York 11794, United States
| | - Katalin Pirisi
- Department
of Biophysics, Medical School, University
of Pecs, Szigeti Street 12, Pecs 7624, Hungary
| | - Samruddhi Jewlikar
- Department
of Chemistry, Stony Brook University, New York, New York 11794, United States
| | - Katrin Adamczyk
- School
of Chemistry, University of East Anglia, Norwich NR4 7TJ, U.K.
| | - Gregory M. Greetham
- Central
Laser Facility, Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot OX11 0QX, U.K.
| | - Michael Towrie
- Central
Laser Facility, Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot OX11 0QX, U.K.
| | - Jeremy R. H. Tame
- Drug
Design Laboratory, Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Yokohama 230-0045, Japan
| | - Stephen R. Meech
- School
of Chemistry, University of East Anglia, Norwich NR4 7TJ, U.K.,
| | - Peter J. Tonge
- Department
of Chemistry, Stony Brook University, New York, New York 11794, United States,
| | - Andras Lukacs
- Department
of Biophysics, Medical School, University
of Pecs, Szigeti Street 12, Pecs 7624, Hungary,
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7
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Zhuang B, Liebl U, Vos MH. Flavoprotein Photochemistry: Fundamental Processes and Photocatalytic Perspectives. J Phys Chem B 2022; 126:3199-3207. [PMID: 35442696 DOI: 10.1021/acs.jpcb.2c00969] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Flavins are highly versatile redox-active and colored cofactors in a large variety of proteins. These do include photoenzymes and photoreceptors, although the vast majority performs non-light-driven physiological functions. Nevertheless, electron transfer between flavins and specific nearby amino acid residues (in particular tyrosine, tryptophan, and presumably histidine and arginine) takes place upon excitation of flavin in many flavoproteins. For oxidized flavoproteins these reactions potentially have a photoprotective role. In this Perspective, we outline work on the characterization of early reaction intermediates not only in the relatively well-studied resting oxidized forms but also in the fully reduced and the intrinsically unstable semireduced forms, where ultrafast photooxidation of flavin was recently demonstrated. Along different lines, flavoprotein-based novel photocatalysts for biotechnological applications are presently emerging, employing both substrate photooxidation and photoreduction strategies. Deep insight into the fundamental flavin photochemical reactions may help in guiding and optimizing their development and in the exploration of novel photocatalytic approaches.
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Affiliation(s)
- Bo Zhuang
- LOB, CNRS, INSERM, Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau Cedex, France
| | - Ursula Liebl
- LOB, CNRS, INSERM, Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau Cedex, France
| | - Marten H Vos
- LOB, CNRS, INSERM, Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau Cedex, France
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8
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Uriarte LM, Vitale R, Niziński S, Hadjidemetriou K, Zala N, Lukacs A, Greetham GM, Sazanovich IV, Weik M, Ruckebusch C, Meech SR, Sliwa M. Structural Information about the trans-to- cis Isomerization Mechanism of the Photoswitchable Fluorescent Protein rsEGFP2 Revealed by Multiscale Infrared Transient Absorption. J Phys Chem Lett 2022; 13:1194-1202. [PMID: 35085441 DOI: 10.1021/acs.jpclett.1c02920] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
RsEGFP2 is a reversibly photoswitchable fluorescent protein used in super-resolved optical microscopies, which can be toggled between a fluorescent On state and a nonfluorescent Off state. Previous time-resolved ultraviolet-visible spectroscopic studies have shown that the Off-to-On photoactivation extends over the femto- to millisecond time scale and involves two picosecond lifetime excited states and four ground state intermediates, reflecting a trans-to-cis excited state isomerization, a millisecond deprotonation, and protein structural reorganizations. Femto- to millisecond time-resolved multiple-probe infrared spectroscopy (TRMPS-IR) can reveal structural aspects of intermediate species. Here we apply TRMPS-IR to rsEGFP2 and implement a Savitzky-Golay derivative analysis to correct for baseline drift. The results reveal that a subpicosecond twisted excited state precursor controls the trans-to-cis isomerization and the chromophore reaches its final position in the protein pocket within 100 ps. A new step with a time constant of 42 ns is reported and assigned to structural relaxation of the protein that occurs prior to the deprotonation of the chromophore on the millisecond time scale.
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Affiliation(s)
- Lucas M Uriarte
- Univ. Lille, CNRS, UMR 8516, LASIRE, Laboratoire de Spectroscopie pour les Interactions, la Réactivité et l'Environnement, Lille 59000, France
| | - Raffaele Vitale
- Univ. Lille, CNRS, UMR 8516, LASIRE, Laboratoire de Spectroscopie pour les Interactions, la Réactivité et l'Environnement, Lille 59000, France
| | - Stanisław Niziński
- Univ. Lille, CNRS, UMR 8516, LASIRE, Laboratoire de Spectroscopie pour les Interactions, la Réactivité et l'Environnement, Lille 59000, France
- Quantum Electronics Laboratory, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, Poznan 61-614, Poland
| | | | - Ninon Zala
- Univ. Grenoble Alpes, CEA, CNRS, Institut de Biologie Structurale, 38000 Grenoble, France
| | - Andras Lukacs
- Department of Biophysics, Medical School, University of Pecs, Szigeti ut 12, 7624 Pecs, Hungary
| | - Gregory M Greetham
- Central Laser Facility, Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot, Oxon OX11 0QX, U.K
| | - Igor V Sazanovich
- Central Laser Facility, Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot, Oxon OX11 0QX, U.K
| | - Martin Weik
- Univ. Grenoble Alpes, CEA, CNRS, Institut de Biologie Structurale, 38000 Grenoble, France
| | - Cyril Ruckebusch
- Univ. Lille, CNRS, UMR 8516, LASIRE, Laboratoire de Spectroscopie pour les Interactions, la Réactivité et l'Environnement, Lille 59000, France
| | - Stephen R Meech
- School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K
| | - Michel Sliwa
- Univ. Lille, CNRS, UMR 8516, LASIRE, Laboratoire de Spectroscopie pour les Interactions, la Réactivité et l'Environnement, Lille 59000, France
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9
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Mathis P, Sage E, Byrdin M. Pushing the limits of flash photolysis to unravel the secrets of biological electron and proton transfer. Photochem Photobiol Sci 2022; 21:1533-1544. [DOI: 10.1007/s43630-021-00134-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/05/2021] [Indexed: 11/25/2022]
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10
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Bin Mohd Yusof MS, Lim YL, Loh ZH. Ultrafast vibrational wave packet dynamics of the aqueous tyrosyl radical anion induced by photodetachment. Phys Chem Chem Phys 2021; 23:18525-18534. [PMID: 34581329 DOI: 10.1039/d1cp02975d] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The ultrafast dynamics triggered by the photodetachment of the tyrosinate dianion in aqueous environment shed light on the elementary processes that accompany the interaction of ionizing radiation with biological matter. Photodetachment of the tryosinate dianion yields the tyrosyl radical anion, an important intermediate in biological redox reactions, although the study of its ultrafast dynamics is limited. Here, we utilize femtosecond optical pump-probe spectroscopy to investigate the ultrafast structural reorganization dynamics that follow the photodetachment of the tyrosinate dianion in aqueous solution. Photodetachment of the tyrosinate dianion leads to vibrational wave packet motion along seven vibrational modes that are coupled to the photodetachment process. The vibrational modes are assigned with the aid of density functional theory (DFT) calculations. Our results offer a glimpse of the elementary dynamics of ionized biomolecules and suggest the possibility of extending this approach to investigate the ionization-induced structural rearrangement of other aromatic amino acids and larger biomolecules.
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Affiliation(s)
- Muhammad Shafiq Bin Mohd Yusof
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore.
| | - Yong Liang Lim
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore.
| | - Zhi-Heng Loh
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore.
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11
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Photochemical processes in flavo-enzymes as a probe for active site dynamics: TrmFO of Thermus thermophilus. Photochem Photobiol Sci 2021; 20:663-670. [PMID: 33977512 DOI: 10.1007/s43630-021-00052-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Accepted: 05/03/2021] [Indexed: 10/21/2022]
Abstract
Quenching of flavin fluorescence by electron transfer from neighboring aromatic residues is ubiquitous in flavoproteins. Apart from constituting a functional process in specific light-active systems, time-resolved spectral characterization of the process can more generally be employed as a probe for the active site configuration and dynamics. In the C51A variant of the bacterial RNA-transforming flavoenzyme TrmFO from the bacterium Thermus thermophilus, fluorescence is very short-lived (~ 1 ps), and close-by Tyr343 is known to act as the main quencher, as confirmed here by the very similar dynamics observed in protein variants with modified other potential quenchers, Trp283 and Trp214. When Tyr343 is modified to redox-inactive phenylalanine, slower and highly multiphasic kinetics are observed on the picosecond-nanosecond timescale, reflecting heterogeneous electron donor-acceptor configurations. We demonstrate that Trp214, which is located on a potentially functional flexible loop, contributes to electron donor quenching in this variant. Contrasting with observations in other nucleic acid-transforming enzymes, these kinetics are strikingly temperature-independent. This indicates (a) near-barrierless electron transfer reactions and (b) no exchange between different configurations on the timescale up to at least 2 ns, despite the presumed flexibility of Trp214. Results of extensive molecular dynamics simulations are presented to explain this unexpected finding in terms of slowly exchanging protein configurations.
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