Structural Plasticity of Reaction Centers from Purple Bacteria

Jones, Michael R.

doi:10.1007/978-1-4020-8815-5_16

Cited by 22 publications

(19 citation statements)

References 197 publications

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“…viridis , but the quinone in this position has been shown by numerous studies (in most cases the UQ 10 in Rba. sphaeroides ) to be replaceable by a large variety of quinone molecules [4,6,32]. Our result implies a possibility of the MQ exchange between the Q A site and quinone pool but at a much reduced rate with respect to the UQ at Q B site, because the binding affinity of the quinone at Q A site is much greater than that of the quinone at Q B site (−21 vs. −11 kJ/mol for Δ G °) [33].…”

Section: Discussionmentioning

confidence: 71%

Characterization of the quinones in purple sulfur bacterium Thermochromatium tepidum

Kimura

Kawakami

et al. 2015

FEBS Letters

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a b s t r a c tQuinone distributions in the thermophilic purple sulfur bacterium Thermochromatium tepidum have been investigated at different levels of the photosynthetic apparatus. Here we show that, on average, the intracytoplasmic membrane contains 18 ubiquinones (UQ) and 4 menaquinones (MQ) per reaction center (RC). About one-third of the quinones are retained in the light-harvest ing-reaction center core complex (LH1-RC) with a similar ratio of UQ to MQ. The numbers of quinones essentially remains unchanged during crystallization of the LH1-RC. There are 1-2 UQ and 1 MQ associated with the RC-only complex in the purified solution sample. Our results suggest that a large proportion of the quinones are confined to the core complex and at least five UQs remain invisible in the current LH1-RC crystal structure.

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Section: Discussionmentioning

confidence: 71%

Characterization of the quinones in purple sulfur bacterium Thermochromatium tepidum

Kimura

Kawakami

et al. 2015

FEBS Letters

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“…Solubilized membranes were ultracentrifuged at 541000g, and six His-tagged RCs were purified from the supernatant using affinity chromatography. 37 The concentration of RCs after purification was determined by their absorption at 804 nm, as described by Goldsmith and Boxer (see the Supporting Information). 38 Planar gold working electrodes (RMS roughness <2 nm) were fabricated by evaporating an adhesion layer of 20 nm of Cr (at a deposition rate of 2 A°/s) followed by 500 nm gold (at a deposition rate of ∼1 A°/s) onto glass substrates (Varian ebeam evaporator).…”

Section: Methodsmentioning

confidence: 99%

“…Membranes were resuspended in 10 mM Tris (pH 8) and 150 mM NaCl and solubilized with 1.5% N , N -dimethyldodecylamine N -oxide (LDAO). Solubilized membranes were ultracentrifuged at 541000 g , and six His-tagged RCs were purified from the supernatant using affinity chromatography . The concentration of RCs after purification was determined by their absorption at 804 nm, as described by Goldsmith and Boxer (see the Supporting Information).…”

Section: Methodsmentioning

confidence: 99%

The Role of Gold-Adsorbed Photosynthetic Reaction Centers and Redox Mediators in the Charge Transfer and Photocurrent Generation in a Bio-Photoelectrochemical Cell

Yaghoubi

Jun

et al. 2012

J. Phys. Chem. C

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Bacterial photosynthetic reaction centers (RCs) are promising materials for solar energy harvesting, due to their high quantum efficiency. A simple approach for making a photovoltaic device is to apply solubilized RCs and charge carrier mediators to the electrolyte of an electrochemical cell. However, the adsorption of analytes on the electrodes can affect the charge transfer from RCs to the electrodes. In this work, photovoltaic devices were fabricated incorporating RCs from purple bacteria, ubiquinone-10 (Q2), and cytochrome c (Cyt c) (the latter two species acting as redox mediators). The adsorption of each of these three species on the gold working electrode was investigated, and the roles of adsorbed species in the photocurrent generation and the cycle of charge transfer were studied by a series of photochronoamperometric, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and cyclic voltammetry (CV) tests. It was shown that both redox mediators were required for photocurrent generation; hence, the RC itself is likely unable to inject electrons into the gold electrode directly. The reverse redox reactions of mediators at the electrodes generates electrical current. Cyclic voltammograms for the RC-exposed gold electrode revealed a redox couple due to the adsorbed RC at ∼ +0.5 V (vs NHE), which confirmed that the RC was still redox active, upon adsorption to the gold. Photochronoamperometric studies also indicated that RCs adsorb, and are strongly bound to the surface of the gold, retaining functionality and contributing significantly to the process of photocurrent generation. Similar experiments showed the adsorption of Q2 and Cyt c on unmodified gold surfaces. It was indicated by the photochronoamperometric tests that the photocurrent derives from Q2-mediated charge transfer between the RCs and the gold electrode, while solubilized Cyt c mediates charge transfer between the P-side of adsorbed RC and the Pt counter electrode. Also, the stability of the adsorbed RCs and mediators was evaluated by measuring the photocurrent response over a period of 1 week. It is found that ∼46% of the adsorbed RCs remain active after a week under aerobic conditions. A significantly extended lifetime is expected by removing oxygen from the electrolyte and sealing the device.

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“…Previous studies have used mutagenesis to examine the role of the protein environment in establishing these electron transfer properties [39,43]. In some cases, alterations of the amino acid residues coordinating cofactors have resulted in the binding of different cofactors, for examining the alteration of a His that coordinates P results in the incorporation of a bacteriopheophytin-bacteriochlorophyll heterodimer [44][45][46].…”

Section: Discussionmentioning

confidence: 99%

A bound iron porphyrin is redox active in hybrid bacterial reaction centers modified to possess a four-helix bundle domain

Allen

Chamberlain

Olson

et al. 2021

Photochem Photobiol Sci

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In this paper we report the design of hybrid reaction centers with a novel redox-active cofactor. Reaction centers perform the primary photochemistry of photosynthesis, namely the light-induced transfer of an electron from the bacteriochlorophyll dimer to a series of electron acceptors. Hybrid complexes were created by the fusion of an artificial four-helix bundle to the M-subunit of the reaction center. Despite the large modification, optical spectra show that the purified hybrid reaction centers assemble as active complexes that retain the characteristic cofactor absorption peaks and are capable of light-induced charge separation. The four-helix bundle could bind iron-protoporphyrin in either a reduced and oxidized state. After binding iron-protoporphyrin to the hybrid reaction centers, light excitation results in a new derivative signal with a maximum at 402 nm and minimum at 429 nm. This signal increases in amplitude with longer light durations and persists in the dark. No signal is observed when iron-protoporphyrin is added to reaction centers without the four-helix bundle domain or when a redox-inactive zinc-protoporphyrin is bound. The results are consistent with the signal arising from a new redox reaction, electron transfer from the iron-protoporphyrin to the oxidized bacteriochlorophyll dimer. These outcomes demonstrate the feasibility of binding porphyrins to the hybrid reaction centers to gain new light-driven functions.

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Structural Plasticity of Reaction Centers from Purple Bacteria

Cited by 22 publications

References 197 publications

Characterization of the quinones in purple sulfur bacterium Thermochromatium tepidum

Characterization of the quinones in purple sulfur bacterium Thermochromatium tepidum

The Role of Gold-Adsorbed Photosynthetic Reaction Centers and Redox Mediators in the Charge Transfer and Photocurrent Generation in a Bio-Photoelectrochemical Cell

A bound iron porphyrin is redox active in hybrid bacterial reaction centers modified to possess a four-helix bundle domain

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