1
|
Significant impact of deprotonated status on the photoisomerization dynamics of bacteriophytochrome chromophore. CHINESE CHEM LETT 2022. [DOI: 10.1016/j.cclet.2022.107850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
2
|
Grigorenko BL, Polyakov IV, Nemukhin AV. Modeling photophysical properties of the bacteriophytochrome-based fluorescent protein IFP1.4. J Chem Phys 2021; 154:065101. [PMID: 33588533 DOI: 10.1063/5.0026475] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
An enhanced interest in the phytochrome-based fluorescent proteins is explained by their ability to absorb and emit light in the far-red and infra-red regions particularly suitable for bioimaging. The fluorescent protein IFP1.4 was engineered from the chromophore-binding domain of a bacteriophytochrome in attempts to increase the fluorescence quantum yield. We report the results of simulations of structures in the ground S0 and excited S1 electronic states of IFP1.4 using the methods of quantum chemistry and quantum mechanics/molecular mechanics. We construct different protonation states of the biliverdin (BV) chromophore in the red-absorbing form of the protein by moving protons from the BV pyrrole rings to a suitable acceptor within the system and show that these structures are close in energy but differ by absorption bands. For the first time, we report structures of the minimum energy conical intersection points S1/S0 on the energy surfaces of BV in the protein environment and describe their connection to the local minima in the excited S1 state. These simulations allow us to characterize the deactivation routes in IFP1.4.
Collapse
Affiliation(s)
- Bella L Grigorenko
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, 119991 Moscow, Russian Federation
| | - Igor V Polyakov
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, 119991 Moscow, Russian Federation
| | - Alexander V Nemukhin
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, 119991 Moscow, Russian Federation
| |
Collapse
|
3
|
Mishima K, Shoji M, Umena Y, Boero M, Shigeta Y. Role of the Propionic Acid Side-Chain of C-Phycocyanin Chromophores in the Excited States for the Photosynthesis Process. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2020. [DOI: 10.1246/bcsj.20200187] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Kenji Mishima
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
| | - Mitsuo Shoji
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
- JST-PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Yasufumi Umena
- Department of Physiology, Division of Biophysics, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan
| | - Mauro Boero
- University of Strasbourg, Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS, UMR 7504, 23 rue du Loess, F-67034 France
| | - Yasuteru Shigeta
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
| |
Collapse
|
4
|
Competing excited-state deactivation processes in bacteriophytochromes. ADVANCES IN QUANTUM CHEMISTRY 2020. [DOI: 10.1016/bs.aiq.2020.05.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
5
|
Bizimana LA, Farfan CA, Brazard J, Turner DB. E to Z Photoisomerization of Phytochrome Cph1Δ Exceeds the Born-Oppenheimer Adiabatic Limit. J Phys Chem Lett 2019; 10:3550-3556. [PMID: 31181167 DOI: 10.1021/acs.jpclett.9b01137] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The Born-Oppenheimer adiabatic limit applies broadly in chemistry because most reactions occur on the ground electronic state. Photochemical reactions involve two or more electronic states and need not be subject to this adiabatic limit. The spectroscopic signatures of nonadiabatic processes are subtle, and therefore, experimental investigations have been limited to the few systems dominated by single photochemical outcomes. Systems with branched excited-state pathways have been neglected, despite their potential to reveal insights into photochemical reactivity. Here we present experimental evidence from coherent three-dimensional electronic spectroscopy that the E to Z photoisomerization of phytochrome Cph1 is strongly nonadiabatic, and the simulations reproduce the measured features only when the photoisomerization proceeds nonadiabatically near, but not through, a conical intersection. The results broaden the general understanding of photoisomerization mechanisms and motivate future studies of nonadiabatic processes with multiple outcomes arising from branching on excited-state potential energy surfaces.
Collapse
Affiliation(s)
- Laurie A Bizimana
- Department of Chemistry , New York University , 100 Washington Square East , New York , New York 10003 , United States
| | - Camille A Farfan
- Department of Chemistry , New York University , 100 Washington Square East , New York , New York 10003 , United States
| | - Johanna Brazard
- Department of Chemistry , New York University , 100 Washington Square East , New York , New York 10003 , United States
| | - Daniel B Turner
- Department of Chemistry , New York University , 100 Washington Square East , New York , New York 10003 , United States
| |
Collapse
|
6
|
Nemukhin AV, Grigorenko BL, Khrenova MG, Krylov AI. Computational Challenges in Modeling of Representative Bioimaging Proteins: GFP-Like Proteins, Flavoproteins, and Phytochromes. J Phys Chem B 2019; 123:6133-6149. [DOI: 10.1021/acs.jpcb.9b00591] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Alexander V. Nemukhin
- Department of Chemistry, Lomonosov Moscow State University, Moscow 119991, Russia
- Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow 119334, Russia
| | - Bella L. Grigorenko
- Department of Chemistry, Lomonosov Moscow State University, Moscow 119991, Russia
- Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow 119334, Russia
| | - Maria G. Khrenova
- Department of Chemistry, Lomonosov Moscow State University, Moscow 119991, Russia
- Federal Research Center of Biotechnology, Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow 119071, Russian
| | - Anna I. Krylov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| |
Collapse
|
7
|
Orozco-Gonzalez Y, Kabir MP, Gozem S. Electrostatic Spectral Tuning Maps for Biological Chromophores. J Phys Chem B 2019; 123:4813-4824. [DOI: 10.1021/acs.jpcb.9b00489] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
| | - Mohammad Pabel Kabir
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Samer Gozem
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| |
Collapse
|
8
|
Modi V, Donnini S, Groenhof G, Morozov D. Protonation of the Biliverdin IXα Chromophore in the Red and Far-Red Photoactive States of a Bacteriophytochrome. J Phys Chem B 2019; 123:2325-2334. [PMID: 30762368 PMCID: PMC6727380 DOI: 10.1021/acs.jpcb.9b01117] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
![]()
The
tetrapyrrole chromophore biliverdin IXα (BV) in the bacteriophytochrome
from Deinococcus radiodurans (DrBphP)
is usually assumed to be fully protonated, but this assumption has
not been systematically validated by experiments or extensive computations.
Here, we use force field molecular dynamics simulations and quantum
mechanics/molecular mechanics calculations with density functional
theory and XMCQDPT2 methods to investigate the effect of the five
most probable protonation forms of BV on structural stability, binding
pocket interactions, and absorption spectra in the two photochromic
states of DrBphP. While agreement with X-ray structural data and measured
UV/vis spectra suggest that in both states the protonated form of
the chromophore dominates, we also find that a minor population with
a deprotonated D-ring could contribute to the red-shifted tail in
the absorption spectra.
Collapse
|
9
|
Li X, Hu D, Xie Y, Lan Z. Analysis of trajectory similarity and configuration similarity in on-the-fly surface-hopping simulation on multi-channel nonadiabatic photoisomerization dynamics. J Chem Phys 2018; 149:244104. [DOI: 10.1063/1.5048049] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Affiliation(s)
- Xusong Li
- CAS Key Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China
- Sino-Danish Center for Education and Research/Sino-Danish College, University of Chinese Academy of Sciences, Beijing 100049, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Deping Hu
- CAS Key Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yu Xie
- The Environmental Research Institute, MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China
| | - Zhenggang Lan
- CAS Key Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China
- Sino-Danish Center for Education and Research/Sino-Danish College, University of Chinese Academy of Sciences, Beijing 100049, China
- The Environmental Research Institute, MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China
| |
Collapse
|
10
|
Gozem S, Luk HL, Schapiro I, Olivucci M. Theory and Simulation of the Ultrafast Double-Bond Isomerization of Biological Chromophores. Chem Rev 2017; 117:13502-13565. [DOI: 10.1021/acs.chemrev.7b00177] [Citation(s) in RCA: 175] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Samer Gozem
- Department
of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Hoi Ling Luk
- Chemistry
Department, Bowling Green State University, Overman Hall, Bowling Green, Ohio 43403, United States
| | - Igor Schapiro
- Fritz
Haber Center for Molecular Dynamics, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Massimo Olivucci
- Chemistry
Department, Bowling Green State University, Overman Hall, Bowling Green, Ohio 43403, United States
- Dipartimento
di Biotecnologie, Chimica e Farmacia, Università di Siena, via A. Moro
2, 53100 Siena, Italy
| |
Collapse
|
11
|
Singer P, Wörner S, Lamparter T, Diller R. Spectroscopic Investigation on the Primary Photoreaction of Bathy Phytochrome Agp2-Pr ofAgrobacterium fabrum: Isomerization in a pH-dependent H-bond Network. Chemphyschem 2016; 17:1288-97. [DOI: 10.1002/cphc.201600199] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Indexed: 11/08/2022]
Affiliation(s)
- Patrick Singer
- Department of Physics; University of Kaiserslautern; Erwin-Schrödinger-Strasse, Geb. 46 67663 Kaiserslautern Germany), Fax: +49-631-205-3902
| | - Sybille Wörner
- Botanical Institute; Karlsruhe Institute of Technology; Kaiserstraße 2 76131 Karlsruhe Germany
| | - Tilman Lamparter
- Botanical Institute; Karlsruhe Institute of Technology; Kaiserstraße 2 76131 Karlsruhe Germany
| | - Rolf Diller
- Department of Physics; University of Kaiserslautern; Erwin-Schrödinger-Strasse, Geb. 46 67663 Kaiserslautern Germany), Fax: +49-631-205-3902
| |
Collapse
|
12
|
Falklöf O, Durbeej B. Steric Effects Govern the Photoactivation of Phytochromes. Chemphyschem 2016; 17:954-7. [DOI: 10.1002/cphc.201501080] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Indexed: 11/05/2022]
Affiliation(s)
- Olle Falklöf
- Division of Theoretical Chemistry, IFM; Linköping University; 581 83 Linköping Sweden
| | - Bo Durbeej
- Division of Theoretical Chemistry, IFM; Linköping University; 581 83 Linköping Sweden
| |
Collapse
|
13
|
Zhuang X, Wang J, Lan Z. Tracking of the Molecular Motion in the Primary Event of Photoinduced Reactions of a Phytochromobilin Model. J Phys Chem B 2013; 117:15976-86. [DOI: 10.1021/jp408799b] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Xuhui Zhuang
- Key
Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong 266101, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
- The
Qingdao Key Lab of Solar Energy Utilization and Energy Storage Technology, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong 266101, P. R. China
| | - Jun Wang
- Key
Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong 266101, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
- The
Qingdao Key Lab of Solar Energy Utilization and Energy Storage Technology, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong 266101, P. R. China
| | - Zhenggang Lan
- Key
Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong 266101, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
- The
Qingdao Key Lab of Solar Energy Utilization and Energy Storage Technology, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong 266101, P. R. China
| |
Collapse
|
14
|
Falklöf O, Durbeej B. Modeling of phytochrome absorption spectra. J Comput Chem 2013; 34:1363-74. [DOI: 10.1002/jcc.23265] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 01/31/2013] [Accepted: 02/07/2013] [Indexed: 11/07/2022]
Affiliation(s)
- Olle Falklöf
- Division of Computational Physics; IFM; Linköping University; SE-581 83; Linköping; Sweden
| | - Bo Durbeej
- Division of Computational Physics; IFM; Linköping University; SE-581 83; Linköping; Sweden
| |
Collapse
|
15
|
Strambi A, Durbeej B. Initial excited-state relaxation of the bilin chromophores of phytochromes: a computational study. Photochem Photobiol Sci 2011; 10:569-79. [DOI: 10.1039/c0pp00307g] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
|
16
|
Durbeej B. On the primary event of phytochrome: quantum chemical comparison of photoreactions at C4, C10 and C15. Phys Chem Chem Phys 2009; 11:1354-61. [PMID: 19224036 DOI: 10.1039/b811813b] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Phytochromes are widespread photoreceptors responsive to red and far-red light that exist in two photochromic forms Pr (inactive) and Pfr (active). The Pr --> Pfr conversion proceeds through a series of events initiated by Z-->E photoisomerization of the tetrapyrrole chromophore, believed to occur at C15 of the methine bridge between rings C and D. Recent crystal structures show that ring D in Pr is less tightly packed by the protein than rings A, B and C, which should favor the C15 reaction over reactions at C4 (AB methine bridge) and C10 (BC). In the present work, quantum chemical methods are used to establish the intrinsic reactivity of the chromophore towards all three possible Z-->E isomerization events in the absence of steric effects and specific interactions with the protein. Using a level of theory that reproduces spectroscopic data with an accuracy of approximately 0.2 eV, it is demonstrated that isolated conditions allow the C10 photoreaction to substantially dominate. This finding suggests that the different degrees of ring-packing observed in the protein are crucial not only to facilitate a reaction at C15, but also to prevent an intrinsically more favorable reaction at C10 from taking place.
Collapse
Affiliation(s)
- Bo Durbeej
- Department of Chemistry, University of Siena, Via Aldo Moro 2, I-53100, Siena, Italy.
| |
Collapse
|
17
|
Matute RA, Contreras R, Pérez-Hernández G, González L. The Chromophore Structure of the Cyanobacterial Phytochrome Cph1 As Predicted by Time-Dependent Density Functional Theory. J Phys Chem B 2008; 112:16253-6. [DOI: 10.1021/jp807471e] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
18
|
Anders Borg O, Durbeej B. Which factors determine the acidity of the phytochromobilin chromophore of plant phytochrome? Phys Chem Chem Phys 2008; 10:2528-37. [PMID: 18446253 DOI: 10.1039/b719190a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Quantum chemical calculations aimed at identifying the factors controlling the acidity of phytochromobilin, the tetrapyrrole chromophore of the plant photoreceptor phytochrome, are reported. Phytochrome is converted from an inactive (Pr) to an active form (Pfr) through a series of events initiated by a Z --> E photoisomerization of phytochromobilin, forming the Lumi-R intermediate, and much controversy exists as to whether the protonation state of the chromophore (cationic in Pr with all nitrogens protonated) changes during the photoactivation. Here, relative ground (S0) and excited-state (S1) pKa s of all four pyrrole moieties of phytochromobilin in all 64 possible configurations with respect to the three methine bridges are calculated in a protein-like environment, using a recently benchmarked level of theory. Accordingly, the relationships between acidity and chromophore geometry and charge distribution, hydrogen bonding, and light absorption are investigated in some detail, and discussed in terms of possible mechanisms making a proton transfer reaction more probable along the Pr --> Pfr reaction than in the parent cationic Pr state. It is found that charge distribution in the cationic species, intra-molecular hydrogen bonding in the neutral, and hydrogen bonding with two highly conserved aspartate and histidine residues have a significant effect on the acidity, while overall chromophore geometry and electronic state are less important factors. Furthermore, based on the calculations, two processes that may facilitate a proton transfer by substantially lowering the pKa s relative to their Pr values are identified: (i) a thermal Z,anti --> Z,syn isomerization at C5, occurring after formation of Lumi-R; (ii) a perturbation of the hydrogen bonding network which in Pr comprises the nitrogens of pyrroles A, B and C and the two aspartate and histidine residues.
Collapse
Affiliation(s)
- O Anders Borg
- Department of Quantum Chemistry, Uppsala University, Box 518, S-75120, Uppsala, Sweden
| | | |
Collapse
|
19
|
Borg OA, Durbeej B. Relative Ground and Excited-State pKa Values of Phytochromobilin in the Photoactivation of Phytochrome: A Computational Study. J Phys Chem B 2007; 111:11554-65. [PMID: 17845025 DOI: 10.1021/jp0727953] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The conversion of the plant photoreceptor phytochrome from an inactive (Pr) to an active form (Pfr) is accomplished by a red-light induced Z --> E photoisomerization of its phytochromobilin chromophore. In recent years, the question whether the photoactivation involves a change in chromophore protonation state has been the subject of many experimental studies. Here, we have used quantum chemical methods to calculate relative ground and excited-state pKa values of the different pyrrole moieties of phytochromobilin in a protein-like environment. Assuming (based on experimental data) a Pr ZaZsZa chromophore and considering isomerizations at C15 and C5, it is found that moieties B and C are the strongest acids both in the ground state and in the bright first singlet excited state, which is rationalized in simple geometric and electronic terms. It is also shown that neither light absorption nor isomerization increases the acidity of phytochromobilin relative to the reference Pr state with all pyrrolenic nitrogens protonated. Hence, provided that the subset of chromophore geometries under investigation is biologically relevant, there appears to be no intrinsic driving force for a proton-transfer event. In a series of benchmark calculations, the performance of ab initio and time-dependent density functional theory methods for excited-state studies of phytochromobilin is evaluated in light of available experimental data.
Collapse
Affiliation(s)
- O Anders Borg
- Department of Quantum Chemistry, Uppsala University, Box 518, S-75120 Uppsala, Sweden
| | | |
Collapse
|
20
|
Durbeej B, Eriksson LA. Protein-bound chromophores astaxanthin and phytochromobilin: excited state quantum chemical studies. Phys Chem Chem Phys 2006; 8:4053-71. [PMID: 17028694 DOI: 10.1039/b605682b] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present an overview of excited state quantum chemical calculations aimed at elucidating controversial issues regarding the photochemistry of the protein-bound chromophores astaxanthin and phytochromobilin. In particular, we show how the application of time-dependent density functional theory and other single-reference quantum chemical excited state methods have contributed to shed new light on the origin of the >0.5 eV bathochromic shift of the electronic absorption by the carotenoid astaxanthin in the protein macromolecular complex crustacyanin, and the mechanism for C15-Z,syn --> C15-E,anti isomerization of the tetrapyrrole phytochromobilin that underlies the photoactivation of the plant photoreceptor phytochrome. Within the approximation that exciton coupling is neglected, the calculations on astaxanthin provide support for the notion that the bathochromic shift, which is responsible for the slate-blue coloration of lobster shell, is due to polarization rather than a conformational change of the chromophore in the protein-bound state. Furthermore, the polarization is attributed to a hydrogen-bonded protonated histidine residue. The calculations on phytochromobilin, in turn, suggest that a stepwise C15-Z,syn --> C15-E,syn (photochemical), C15-E,syn --> C15-E,anti (thermal) mechanism is much more favorable than a concerted, fully photochemical mechanism, and that neutral forms of the chromophore are much less likely to photoisomerize than the parent, protonated form. Accordingly, the calculations indirectly support the view that the photoactivation of phytochrome does not involve a proton transfer from the chromophore to the surrounding protein.
Collapse
Affiliation(s)
- Bo Durbeej
- Department of Chemistry, University of Siena, Via Aldo Moro 2, I-53100, Siena, Italy.
| | | |
Collapse
|