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Photosynthetic reaction center variants made via genetic code expansion show Tyr at M210 tunes the initial electron transfer mechanism. Proc Natl Acad Sci U S A 2021; 118:2116439118. [PMID: 34907018 DOI: 10.1073/pnas.2116439118] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/02/2021] [Indexed: 11/18/2022] Open
Abstract
Photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides were engineered to vary the electronic properties of a key tyrosine (M210) close to an essential electron transfer component via its replacement with site-specific, genetically encoded noncanonical amino acid tyrosine analogs. High fidelity of noncanonical amino acid incorporation was verified with mass spectrometry and X-ray crystallography and demonstrated that RC variants exhibit no significant structural alterations relative to wild type (WT). Ultrafast transient absorption spectroscopy indicates the excited primary electron donor, P*, decays via a ∼4-ps and a ∼20-ps population to produce the charge-separated state P+HA - in all variants. Global analysis indicates that in the ∼4-ps population, P+HA - forms through a two-step process, P*→ P+BA -→ P+HA -, while in the ∼20-ps population, it forms via a one-step P* → P+HA - superexchange mechanism. The percentage of the P* population that decays via the superexchange route varies from ∼25 to ∼45% among variants, while in WT, this percentage is ∼15%. Increases in the P* population that decays via superexchange correlate with increases in the free energy of the P+BA - intermediate caused by a given M210 tyrosine analog. This was experimentally estimated through resonance Stark spectroscopy, redox titrations, and near-infrared absorption measurements. As the most energetically perturbative variant, 3-nitrotyrosine at M210 creates an ∼110-meV increase in the free energy of P+BA - along with a dramatic diminution of the 1,030-nm transient absorption band indicative of P+BA - formation. Collectively, this work indicates the tyrosine at M210 tunes the mechanism of primary electron transfer in the RC.
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2
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Tamura H, Saito K, Ishikita H. The origin of unidirectional charge separation in photosynthetic reaction centers: nonadiabatic quantum dynamics of exciton and charge in pigment-protein complexes. Chem Sci 2021; 12:8131-8140. [PMID: 34194703 PMCID: PMC8208306 DOI: 10.1039/d1sc01497h] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 05/03/2021] [Indexed: 11/21/2022] Open
Abstract
Exciton charge separation in photosynthetic reaction centers from purple bacteria (PbRC) and photosystem II (PSII) occurs exclusively along one of the two pseudo-symmetric branches (active branch) of pigment-protein complexes. The microscopic origin of unidirectional charge separation in photosynthesis remains controversial. Here we elucidate the essential factors leading to unidirectional charge separation in PbRC and PSII, using nonadiabatic quantum dynamics calculations in conjunction with time-dependent density functional theory (TDDFT) with the quantum mechanics/molecular mechanics/polarizable continuum model (QM/MM/PCM) method. This approach accounts for energetics, electronic coupling, and vibronic coupling of the pigment excited states under electrostatic interactions and polarization of whole protein environments. The calculated time constants of charge separation along the active branches of PbRC and PSII are similar to those observed in time-resolved spectroscopic experiments. In PbRC, Tyr-M210 near the accessary bacteriochlorophyll reduces the energy of the intermediate state and drastically accelerates charge separation overcoming the electron-hole interaction. Remarkably, even though both the active and inactive branches in PSII can accept excitons from light-harvesting complexes, charge separation in the inactive branch is prevented by a weak electronic coupling due to symmetry-breaking of the chlorophyll configurations. The exciton in the inactive branch in PSII can be transferred to the active branch via direct and indirect pathways. Subsequently, the ultrafast electron transfer to pheophytin in the active branch prevents exciton back transfer to the inactive branch, thereby achieving unidirectional charge separation.
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Affiliation(s)
- Hiroyuki Tamura
- Department of Applied Chemistry, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8654 Japan
- Research Center for Advanced Science and Technology, The University of Tokyo 4-6-1 Komaba, Meguro-ku Tokyo 153-8904 Japan
| | - Keisuke Saito
- Department of Applied Chemistry, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8654 Japan
- Research Center for Advanced Science and Technology, The University of Tokyo 4-6-1 Komaba, Meguro-ku Tokyo 153-8904 Japan
| | - Hiroshi Ishikita
- Department of Applied Chemistry, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8654 Japan
- Research Center for Advanced Science and Technology, The University of Tokyo 4-6-1 Komaba, Meguro-ku Tokyo 153-8904 Japan
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3
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Lin CY, Boxer SG. Mechanism of Color and Photoacidity Tuning for the Protonated Green Fluorescent Protein Chromophore. J Am Chem Soc 2020; 142:11032-11041. [PMID: 32453950 DOI: 10.1021/jacs.0c02796] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The neutral or A state of the green fluorescent protein (GFP) chromophore is a remarkable example of a photoacid naturally embedded in the protein environment and accounts for the large Stokes shift of GFP in response to near UV excitation. Its color tuning mechanism has been largely overlooked, as it is less preferred for imaging applications than the redder anionic or B state. Past studies, based on site-directed mutagenesis or solvatochromism of the isolated chromophore, have concluded that its color tuning range is much narrower than its anionic counterpart. However, as we performed extensive investigation on more GFP mutants, we found that the color of the neutral chromophore can be more sensitive to protein electrostatics than can the anionic counterpart. Electronic Stark spectroscopy reveals a fundamentally different electrostatic color tuning mechanism for the neutral state of the chromophore that demands a three-form model as compared to that of the anionic state, which requires only two forms ( J. Am. Chem. Soc. 2019, 141, 15250-15265). Specifically, an underlying zwitterionic charge-transfer state is required to explain its sensitivity to electrostatics. As the Stokes shift is tightly linked to excited-state proton transfer (ESPT) of the protonated chromophore, we infer design principles of the GFP chromophore as a photoacid through the color tuning mechanisms of both protonation states. The three-form model could also be applied to similar biological and nonbiological dyes and complements the failure of the two-form model for donor-acceptor systems with localized ground-state electronic distributions.
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Affiliation(s)
- Chi-Yun Lin
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Steven G Boxer
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
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Sevinc PC, Dhital B, Govind Rao V, Wang Y, Lu HP. Probing Electric Field Effect on Covalent Interactions at a Molecule–Semiconductor Interface. J Am Chem Soc 2016; 138:1536-42. [PMID: 26735967 DOI: 10.1021/jacs.5b10253] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Papatya C. Sevinc
- Department of Chemistry and
Center for Photochemical Sciences, Bowling Green State University, Bowling
Green, Ohio 43403, United States
| | - Bharat Dhital
- Department of Chemistry and
Center for Photochemical Sciences, Bowling Green State University, Bowling
Green, Ohio 43403, United States
| | - Vishal Govind Rao
- Department of Chemistry and
Center for Photochemical Sciences, Bowling Green State University, Bowling
Green, Ohio 43403, United States
| | - Yuanmin Wang
- Department of Chemistry and
Center for Photochemical Sciences, Bowling Green State University, Bowling
Green, Ohio 43403, United States
| | - H. Peter Lu
- Department of Chemistry and
Center for Photochemical Sciences, Bowling Green State University, Bowling
Green, Ohio 43403, United States
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5
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Saggu M, Carter B, Zhou X, Faries K, Cegelski L, Holten D, Boxer SG, Kirmaier C. Putative hydrogen bond to tyrosine M208 in photosynthetic reaction centers from Rhodobacter capsulatus significantly slows primary charge separation. J Phys Chem B 2014; 118:6721-32. [PMID: 24902471 PMCID: PMC4064694 DOI: 10.1021/jp503422c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
![]()
Slow, ∼50
ps, P* → P+HA– electron
transfer is observed in Rhodobacter
capsulatus reaction centers (RCs) bearing the native
Tyr residue at M208 and the single amino acid change of isoleucine
at M204 to glutamic acid. The P* decay kinetics are unusually homogeneous
(single exponential) at room temperature. Comparative solid-state
NMR of [4′-13C]Tyr labeled wild-type and M204E RCs
show that the chemical shift of Tyr M208 is significantly altered
in the M204E mutant and in a manner consistent with formation of a
hydrogen bond to the Tyr M208 hydroxyl group. Models based on RC crystal
structure coordinates indicate that if such a hydrogen bond is formed
between the Glu at M204 and the M208 Tyr hydroxyl group, the −OH
would be oriented in a fashion expected (based on the calculations
by Alden et al., J. Phys. Chem.1996, 100, 16761–16770) to destabilize P+BA– in free energy. Alteration
of the environment of Tyr M208 and BA by Glu M204 via this
putative hydrogen bond has a powerful influence on primary charge
separation.
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Affiliation(s)
- Miguel Saggu
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
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6
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Guo Z, Lin S, Woodbury NW. Utilizing the Dynamic Stark Shift as a Probe for Dielectric Relaxation in Photosynthetic Reaction Centers During Charge Separation. J Phys Chem B 2013; 117:11383-90. [DOI: 10.1021/jp4037843] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Zhi Guo
- The
Biodesign Institute at Arizona State University, ‡Department of Chemistry and Biochemistry, and §Department of
Physics, Arizona State University, Tempe, Arizona 85287-5201, United States
| | - Su Lin
- The
Biodesign Institute at Arizona State University, ‡Department of Chemistry and Biochemistry, and §Department of
Physics, Arizona State University, Tempe, Arizona 85287-5201, United States
| | - Neal W. Woodbury
- The
Biodesign Institute at Arizona State University, ‡Department of Chemistry and Biochemistry, and §Department of
Physics, Arizona State University, Tempe, Arizona 85287-5201, United States
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Wang H, Hao Y, Jiang Y, Lin S, Woodbury NW. Role of Protein Dynamics in Guiding Electron-Transfer Pathways in Reaction Centers from Rhodobacter sphaeroides. J Phys Chem B 2011; 116:711-7. [DOI: 10.1021/jp211702b] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Haiyu Wang
- State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
- The Biodesign Institute, and Department of Chemistry and Biochemistry, Arizona State University, 1001 McAllister Ave., Tempe, Arizona 85287, United States
| | - Yawei Hao
- State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Ying, Jiang
- State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Su Lin
- The Biodesign Institute, and Department of Chemistry and Biochemistry, Arizona State University, 1001 McAllister Ave., Tempe, Arizona 85287, United States
| | - Neal W. Woodbury
- The Biodesign Institute, and Department of Chemistry and Biochemistry, Arizona State University, 1001 McAllister Ave., Tempe, Arizona 85287, United States
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Affiliation(s)
- Steven G. Boxer
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
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9
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Williams JC, Allen JP. Directed Modification of Reaction Centers from Purple Bacteria. THE PURPLE PHOTOTROPHIC BACTERIA 2009. [DOI: 10.1007/978-1-4020-8815-5_18] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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10
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Wang H, Lin S, Katilius E, Laser C, Allen JP, Williams JC, Woodbury NW. Unusual Temperature Dependence of Photosynthetic Electron Transfer due to Protein Dynamics. J Phys Chem B 2008; 113:818-24. [DOI: 10.1021/jp807468c] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Haiyu Wang
- The Biodesign Institute at Arizona State University, 1001 South McAllister Avenue, Tempe, Arizona 85287-5201, and The Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604
| | - Su Lin
- The Biodesign Institute at Arizona State University, 1001 South McAllister Avenue, Tempe, Arizona 85287-5201, and The Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604
| | - Evaldas Katilius
- The Biodesign Institute at Arizona State University, 1001 South McAllister Avenue, Tempe, Arizona 85287-5201, and The Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604
| | - Christa Laser
- The Biodesign Institute at Arizona State University, 1001 South McAllister Avenue, Tempe, Arizona 85287-5201, and The Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604
| | - James P. Allen
- The Biodesign Institute at Arizona State University, 1001 South McAllister Avenue, Tempe, Arizona 85287-5201, and The Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604
| | - JoAnn C. Williams
- The Biodesign Institute at Arizona State University, 1001 South McAllister Avenue, Tempe, Arizona 85287-5201, and The Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604
| | - Neal W. Woodbury
- The Biodesign Institute at Arizona State University, 1001 South McAllister Avenue, Tempe, Arizona 85287-5201, and The Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604
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11
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Wang H, Lin S, Woodbury NW. Excitation wavelength dependence of primary charge separation in reaction centers from Rhodobacter sphaeroides. J Phys Chem B 2008; 112:14296-301. [PMID: 18939793 DOI: 10.1021/jp8058799] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The excitation wavelength dependence of the initial electron transfer rate in both wild type and mutant reaction centers from Rhodobacter sphaeroides has been studied between 840 and 920 nm as a function of temperature (10-295 K). The dynamics of primary charge separation show no resolvable excitation wavelength dependence at room temperature over this spectral range. A small variation in rate with excitation wavelength is observed at cryogenic temperatures. The low temperature results cannot be explained in terms either of a nonequilibrium model that assumes that the primary charge separation starts from a vibrationally hot state or a model that assumes a static inhomogeneous distribution of electron transfer driving forces. Instead these results are consistent with the concept that primary charge separation kinetics are controlled by the dynamics of protein conformational diffusion.
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Affiliation(s)
- Haiyu Wang
- Biodesign Institute at Arizona State University and Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-5201, USA
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12
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Treynor TP, Boxer SG. Probing Excited-State Electron Transfer by Resonance Stark Spectroscopy: 3. Theoretical Foundations and Practical Applications. J Phys Chem B 2004. [DOI: 10.1021/jp048988x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Thomas P. Treynor
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
| | - Steven G. Boxer
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
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