scholarly journals An examination of how structural changes can affect the rate of electron transfer in a mutated bacterial photoreaction centre

2000 ◽  
Vol 351 (3) ◽  
pp. 567-578 ◽  
Author(s):  
Justin P. RIDGE ◽  
Paul K. FYFE ◽  
Katherine E. McAULEY ◽  
Marion E. VAN BREDERODE ◽  
Bruno ROBERT ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Structural Changes ◽  
Structural Model ◽  
Transient Absorption ◽  
Photosynthetic Bacterium ◽  
Primary Electron ◽  
Interface Region ◽  
Reaction Centre ◽  
Primary Donor ◽  
Out Of Plane

A series of reaction centres bearing mutations at the (Phe) M197 position were constructed in the photosynthetic bacterium Rhodobacter sphaeroides. This residue is adjacent to the pair of bacteriochlorophyll molecules (PL and PM) that is the primary donor of electrons (P) in photosynthetic light-energy transduction. All of the mutations affected the optical and electrochemical properties of the P bacteriochlorophylls. A mutant reaction centre with the change Phe M197 to Arg (FM197R) was crystallized, and a structural model constructed at 2.3 Å (1Å = 0.1nm) resolution. The mutation resulted in a change in the structure of the protein at the interface region between the P bacteriochlorophylls and the monomeric bacteriochlorophyll that is the first electron acceptor (BL). The new Arg residue at the M197 position undergoes a significant reorientation, creating a cavity at the interface region between P and BL. The acetyl carbonyl substituent group of the PM bacteriochlorophyll undergoes an out-of-plane rotation, which decreases the edge-to-edge distance between the macrocycles of PM and BL. In addition, two new buried water molecules partially filled the cavity that is created by the reorientation of the Arg residue. These waters are in a suitable position to connect the macrocycles of P and BL via three hydrogen bonds. Transient absorption measurements show that, despite an inferred decrease in the driving force for primary electron transfer in the FM197R reaction centre, there is little effect on the overall rate of the primary reaction in the bulk of the reaction-centre population. Examination of the X-ray crystal structure reveals a number of small changes in the structure of the reaction centre in the interface region between the P and BL bacteriochlorophylls that could account for this faster-than-predicted rate of primary electron transfer.

Photosynthetic Reaction Center Variants Made via Genetic Code Expansion Show Tyr at M210 Tunes the Initial Electron Transfer Mechanism

2021 ◽  
Author(s):  
Jared Weaver ◽  
Chi-Yun Lin ◽  
Kaitlyn M. Faries ◽  
Irimpan Mathews ◽  
Silvia Russi ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Free Energy ◽  
Amino Acid ◽  
Near Infrared ◽  
Transient Absorption ◽  
Global Analysis ◽  
Primary Electron ◽  
Wild Type ◽  
Electron Transfer Mechanism ◽  
Noncanonical Amino Acid

Photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides were engineered to vary the electronic properties of a key tyrosine close to an essential electron transfer component (M210) 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. Ultrafast transient absorption spectroscopy indicates the excited primary electron donor, P*, decays via an approximately 4 ps and 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 2-step process P* –> P+BA– –> P+HA-, while in the 20 ps population it forms via a 1-step P* –> P+HA– superexchange mechanism. The percentage of P* population that decays via the superexchange route varies from approximately 25% to 45% among variants while in wild-type this percentage is approximately 15%. Increases in the P* population which decays via superexchange correlates with increases in 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 approximately 110 meV increase in the free energy of P+BA– along with a dramatic diminution of the 1030 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.<br>

WAVE PACKET MOTIONS COUPLED TO ELECTRON TRANSFER IN REACTION CENTERS OF CHLOROFLEXUS AURANTIACUS

2008 ◽  
Vol 06 (04) ◽  
pp. 643-666 ◽  
Author(s):  
ANDREI G. YAKOVLEV ◽  
TATIANA A. SHKUROPATOVA ◽  
LYUDMILA G. VASILIEVA ◽  
ANATOLI YA. SHKUROPATOV ◽  
VLADIMIR A. SHUVALOV
Keyword(s):  
Electron Transfer ◽  
Absorption Band ◽  
Wave Packet ◽  
Transient Absorption ◽  
Primary Electron ◽  
Reaction Centers ◽  
Stimulated Emission ◽  
Spectral Evolution ◽  
Absorption Bands ◽  
Absorbance Changes

Transient absorption difference spectroscopy with ~20 femtosecond (fs) resolution was applied to study the time and spectral evolution of low-temperature (90 K) absorbance changes in isolated reaction centers (RCs) of Chloroflexus (C.) aurantiacus. In RCs, the composition of the B-branch chromophores is different with respect to that of purple bacterial RCs by occupying the BB binding site of accessory bacteriochlorophyll by bacteriopheophytin molecule (ΦB). It was found that the nuclear wave packet motion induced on the potential energy surface of the excited state of the primary electron donor P* by ~20 fs excitation leads to a coherent formation of the states [Formula: see text] and [Formula: see text] (BA is a bacteriochlorophyll monomer in the A-branch of cofactors). The processes were studied by measuring coherent oscillations in kinetics of the absorbance changes at 900 nm and 940 nm (P* stimulated emission), at 750 nm and 785 nm (ΦB absorption bands), and at 1,020–1028 nm ([Formula: see text] absorption band). In RCs, the immediate bleaching of the P band at 880 nm and the appearance of the stimulated wave packet emission at 900 nm were accompanied (with a small delay of 10–20 fs) by electron transfer from P* to the B-branch with bleaching of the ΦB absorption band at 785 nm due to [Formula: see text] formation. These data are consistent with recent measurements for the mutant HM182L Rb. sphaeroides RCs (Yakovlev et al., Biochim Biophys Acta1757:369–379, 2006). Only at a delay of 120 fs was the electron transfer from P* to the A-branch observed with a development of the [Formula: see text] absorption band at 1028 nm. This development was in phase with the appearance of the P* stimulated emission at 940 nm. The data on the A-branch electron transfer in C. aurantiacus RCs are consistent with those observed in native RCs of Rb. sphaeroides. The mechanism of charge separation in RCs with the modified B-branch pigment composition is discussed in terms of coupling between the nuclear wave packet motion and electron transfer from P* to ΦB and BA primary acceptors in the B-branch and A-branch, respectively.

scholarly journals What is β–carotene doing in the photosystem II reaction centre?

2002 ◽  
Vol 357 (1426) ◽  
pp. 1431-1440 ◽  
Author(s):  
Alison Telfer
Keyword(s):  
Electron Transfer ◽  
Photosystem Ii ◽  
Excitation Energy ◽  
Triplet State ◽  
Singlet Oxygen ◽  
Spin Exchange ◽  
Primary Electron ◽  
Triplet States ◽  
Reaction Centre ◽  
Β Carotene

During photosynthesis carotenoids normally serve as antenna pigments, transferring singlet excitation energy to chlorophyll, and preventing singlet oxygen production from chlorophyll triplet states, by rapid spin exchange and decay of the carotenoid triplet to the ground state. The presence of two β–carotene molecules in the photosystem II reaction centre (RC) now seems well established, but they do not quench the triplet state of the primary electron–donor chlorophylls, which are known as P 680 . The β–carotenes cannot be close enough to P 680 for triplet quenching because that would also allow extremely fast electron transfer from β–carotene to P + 680 , preventing the oxidation of water. Their transfer of excitation energy to chlorophyll, though not very efficient, indicates close proximity to the chlorophylls ligated by histidine 118 towards the periphery of the two main RC polypeptides. The primary function of the β–carotenes is probably the quenching of singlet oxygen produced after charge recombination to the triplet state of P 680 . Only when electron donation from water is disturbed does β–carotene become oxidized. One β–carotene can mediate cyclic electron transfer via cytochrome b 559. The other is probably destroyed upon oxidation, which might trigger a breakdown of the polypeptide that binds the cofactors that carry out charge separation.

scholarly journals Photosynthetic reaction center variants made via genetic code expansion show Tyr at M210 tunes the initial electron transfer mechanism

2021 ◽  
Vol 118 (51) ◽  
pp. e2116439118
Author(s):  
Jared Bryce Weaver ◽  
Chi-Yun Lin ◽  
Kaitlyn M. Faries ◽  
Irimpan I. Mathews ◽  
Silvia Russi ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Free Energy ◽  
Amino Acid ◽  
Near Infrared ◽  
Transient Absorption ◽  
Global Analysis ◽  
Primary Electron ◽  
Transient Absorption Spectroscopy ◽  
Electron Transfer Mechanism ◽  
Noncanonical Amino Acid

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.

Photosynthetic Reaction Center Variants Made via Genetic Code Expansion Show Tyr at M210 Tunes the Initial Electron Transfer Mechanism

2021 ◽  
Author(s):  
Jared Weaver ◽  
Chi-Yun Lin ◽  
Kaitlyn M. Faries ◽  
Irimpan Mathews ◽  
Silvia Russi ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Free Energy ◽  
Amino Acid ◽  
Near Infrared ◽  
Transient Absorption ◽  
Global Analysis ◽  
Primary Electron ◽  
Wild Type ◽  
Electron Transfer Mechanism ◽  
Noncanonical Amino Acid

Photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides were engineered to vary the electronic properties of a key tyrosine close to an essential electron transfer component (M210) 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. Ultrafast transient absorption spectroscopy indicates the excited primary electron donor, P*, decays via an approximately 4 ps and 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 2-step process P* –> P+BA– –> P+HA-, while in the 20 ps population it forms via a 1-step P* –> P+HA– superexchange mechanism. The percentage of P* population that decays via the superexchange route varies from approximately 25% to 45% among variants while in wild-type this percentage is approximately 15%. Increases in the P* population which decays via superexchange correlates with increases in 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 approximately 110 meV increase in the free energy of P+BA– along with a dramatic diminution of the 1030 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.<br>

scholarly journals Photosynthetic Reaction Center Variants Made via Genetic Code Expansion Show Tyr at M210 Tunes the Initial Electron Transfer Mechanism

2021 ◽  
Author(s):  
Jared Weaver ◽  
Chi-Yun Lin ◽  
Kaitlyn M. Faries ◽  
Irimpan Mathews ◽  
Silvia Russi ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Free Energy ◽  
Amino Acid ◽  
Near Infrared ◽  
Transient Absorption ◽  
Global Analysis ◽  
Primary Electron ◽  
Wild Type ◽  
Electron Transfer Mechanism ◽  
Noncanonical Amino Acid

Photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides were engineered to vary the electronic properties of a key tyrosine close to an essential electron transfer component (M210) 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. Ultrafast transient absorption spectroscopy indicates the excited primary electron donor, P*, decays via an approximately 4 ps and 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 2-step process P* –> P+BA– –> P+HA-, while in the 20 ps population it forms via a 1-step P* –> P+HA– superexchange mechanism. The percentage of P* population that decays via the superexchange route varies from approximately 25% to 45% among variants while in wild-type this percentage is approximately 15%. Increases in the P* population which decays via superexchange correlates with increases in 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 approximately 110 meV increase in the free energy of P+BA– along with a dramatic diminution of the 1030 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.

scholarly journals Ultrafast Dynamical Study Using Time-resolved Laue Diffraction

2014 ◽  
Vol 70 (a1) ◽  
pp. C766-C766
Author(s):  
Sreevidya Thekku Veedu
Keyword(s):  
Electron Transfer ◽  
Time Scales ◽  
Structural Changes ◽  
Reaction Centre ◽  
Dynamical Study ◽  
Light Harvesting Complexes ◽  
Time Resolved ◽  
Wide Range ◽  
Donor Acceptor ◽  
Excitation Processes

Electron transfer reactions are fundamental processes in chemistry and also in biology [1-3]. Light harvesting complexes are functional centers in plants where sunlight is converted into chemical energy. In this, optical excitation in a chromophore unit leads to the transfer of electrons within the system. However, due to the complexity of the biological photo-reaction centre, recent spectroscopic efforts have concentrated on a smaller chemical model which share characteristic with their biological counter parts. A promising model is the so-called D-A (donor-acceptor) systems, which are chemically synthetic molecules with electron transfer capabilities. The electrical conductivity is a function of the optical state of the system. An optically switching diode is an interesting application of donor-acceptor molecules. We aimed to determine photo-induced structural changes in Pyrene-N,N-dimethylaniline (PyDMA). Static structures for many molecules are available at high resolution but the mechanism by which these molecules function and the structures of intermediate states often remain elusive. Knowledge of the geometry of molecular excited states at atomic resolution is crucial for a full understanding of photo-induced chemical processes. Time-resolved X-ray diffraction (TR-XRD) using polychromatic synchrotron radiation allows a detailed study of the time evolution of structural intermediates and short living states of chemical systems at wide range of time-scales, drawing a complete picture of the photo-induced charge transfer process. Investigation of photo-excitation processes in molecular single crystals, where the initial photo-excitation processes occur on extremely short time-scales (femto-/picosecond time domain) and have been in the focus of scientific investigations due to their possible applications, e.g. as optical switches.

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