6 results on '"Proctor MS"'
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2. Twisted Carotenoids Do Not Support Efficient Intramolecular Singlet Fission in the Orange Carotenoid Protein.
- Author
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Sutherland GA, Pidgeon JP, Lee HKH, Proctor MS, Hitchcock A, Wang S, Chekulaev D, Tsoi WC, Johnson MP, Hunter CN, and Clark J
- Subjects
- Spectrum Analysis methods, Bacterial Proteins chemistry, Light, Carotenoids chemistry, Canthaxanthin
- Abstract
Singlet exciton fission is the spin-allowed generation of two triplet electronic excited states from a singlet state. Intramolecular singlet fission has been suggested to occur on individual carotenoid molecules within protein complexes provided that the conjugated backbone is twisted out of plane. However, this hypothesis has been forwarded only in protein complexes containing multiple carotenoids and bacteriochlorophylls in close contact. To test the hypothesis on twisted carotenoids in a "minimal" one-carotenoid system, we study the orange carotenoid protein (OCP). OCP exists in two forms: in its orange form (OCPo), the single bound carotenoid is twisted, whereas in its red form (OCPr), the carotenoid is planar. To enable room-temperature spectroscopy on canthaxanthin-binding OCPo and OCPr without laser-induced photoconversion, we trap them in a trehalose glass. Using transient absorption spectroscopy, we show that there is no evidence of long-lived triplet generation through intramolecular singlet fission despite the canthaxanthin twist in OCPo.
- Published
- 2023
- Full Text
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3. High cyclic electron transfer via the PGR5 pathway in the absence of photosynthetic control.
- Author
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Degen GE, Jackson PJ, Proctor MS, Zoulias N, Casson SA, and Johnson MP
- Subjects
- Protons, Electrons, NADP metabolism, Carbon Dioxide metabolism, Photosynthesis, Electron Transport, Photosystem I Protein Complex genetics, Photosystem I Protein Complex metabolism, Adenosine Triphosphate metabolism, Arabidopsis Proteins metabolism, Arabidopsis metabolism, Photosynthetic Reaction Center Complex Proteins genetics, Photosynthetic Reaction Center Complex Proteins metabolism
- Abstract
The light reactions of photosynthesis couple electron and proton transfers across the thylakoid membrane, generating NADPH, and proton motive force (pmf) that powers the endergonic synthesis of ATP by ATP synthase. ATP and NADPH are required for CO2 fixation into carbohydrates by the Calvin-Benson-Bassham cycle. The dominant ΔpH component of the pmf also plays a photoprotective role in regulating photosystem II light harvesting efficiency through nonphotochemical quenching (NPQ) and photosynthetic control via electron transfer from cytochrome b6f (cytb6f) to photosystem I. ΔpH can be adjusted by increasing the proton influx into the thylakoid lumen via upregulation of cyclic electron transfer (CET) or decreasing proton efflux via downregulation of ATP synthase conductivity (gH+). The interplay and relative contributions of these two elements of ΔpH control to photoprotection are not well understood. Here, we showed that an Arabidopsis (Arabidopsis thaliana) ATP synthase mutant hunger for oxygen in photosynthetic transfer reaction 2 (hope2) with 40% higher proton efflux has supercharged CET. Double crosses of hope2 with the CET-deficient proton gradient regulation 5 and ndh-like photosynthetic complex I lines revealed that PROTON GRADIENT REGULATION 5 (PGR5)-dependent CET is the major pathway contributing to higher proton influx. PGR5-dependent CET allowed hope2 to maintain wild-type levels of ΔpH, CO2 fixation and NPQ, however photosynthetic control remained absent and PSI was prone to photoinhibition. Therefore, high CET in the absence of ATP synthase regulation is insufficient for PSI photoprotection., Competing Interests: Conflict of interest statement. None declared., (© American Society of Plant Biologists 2023. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)
- Published
- 2023
- Full Text
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4. Zeta-Carotene Isomerase (Z-ISO) Is Required for Light-Independent Carotenoid Biosynthesis in the Cyanobacterium Synechocystis sp. PCC 6803.
- Author
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Proctor MS, Morey-Burrows FS, Canniffe DP, Martin EC, Swainsbury DJK, Johnson MP, Hunter CN, Sutherland GA, and Hitchcock A
- Abstract
Carotenoids are crucial photosynthetic pigments utilized for light harvesting, energy transfer, and photoprotection. Although most of the enzymes involved in carotenoid biosynthesis in chlorophototrophs are known, some are yet to be identified or fully characterized in certain organisms. A recently characterized enzyme in oxygenic phototrophs is 15- cis -zeta(ζ)-carotene isomerase (Z-ISO), which catalyzes the cis -to- trans isomerization of the central 15-15' cis double bond in 9,15,9'-tri- cis -ζ-carotene to produce 9,9'-di- cis -ζ-carotene during the four-step conversion of phytoene to lycopene. Z-ISO is a heme B-containing enzyme best studied in angiosperms. Homologs of Z-ISO are present in organisms that use the multi-enzyme poly- cis phytoene desaturation pathway, including algae and cyanobacteria, but appear to be absent in green bacteria. Here we confirm the identity of Z-ISO in the model unicellular cyanobacterium Synechocystis sp. PCC 6803 by showing that the protein encoded by the slr1599 open reading frame has ζ-carotene isomerase activity when produced in Escherichia coli . A Synechocystis Δslr1599 mutant synthesizes a normal quota of carotenoids when grown under illumination, where the photolabile 15-15' cis double bond of 9,15,9'-tri- cis -ζ-carotene is isomerized by light, but accumulates this intermediate and fails to produce 'mature' carotenoid species during light-activated heterotrophic growth, demonstrating the requirement of Z-ISO for carotenoid biosynthesis during periods of darkness. In the absence of a structure of Z-ISO, we analyze AlphaFold models of the Synechocystis , Zea mays (maize), and Arabidopsis thaliana enzymes, identifying putative protein ligands for the heme B cofactor and the substrate-binding site.
- Published
- 2022
- Full Text
- View/download PDF
5. Cryo-EM structures of the Synechocystis sp. PCC 6803 cytochrome b6f complex with and without the regulatory PetP subunit.
- Author
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Proctor MS, Malone LA, Farmer DA, Swainsbury DJK, Hawkings FR, Pastorelli F, Emrich-Mills TZ, Siebert CA, Hunter CN, Johnson MP, and Hitchcock A
- Subjects
- Cryoelectron Microscopy, Electron Transport physiology, Photosynthesis, Thylakoids genetics, Thylakoids metabolism, Cytochrome b6f Complex chemistry, Cytochrome b6f Complex metabolism, Cytochrome b6f Complex physiology, Synechocystis metabolism, Synechocystis physiology
- Abstract
In oxygenic photosynthesis, the cytochrome b6f (cytb6f) complex links the linear electron transfer (LET) reactions occurring at photosystems I and II and generates a transmembrane proton gradient via the Q-cycle. In addition to this central role in LET, cytb6f also participates in a range of processes including cyclic electron transfer (CET), state transitions and photosynthetic control. Many of the regulatory roles of cytb6f are facilitated by auxiliary proteins that differ depending upon the species, yet because of their weak and transient nature the structural details of these interactions remain unknown. An apparent key player in the regulatory balance between LET and CET in cyanobacteria is PetP, a ∼10 kDa protein that is also found in red algae but not in green algae and plants. Here, we used cryogenic electron microscopy to determine the structure of the Synechocystis sp. PCC 6803 cytb6f complex in the presence and absence of PetP. Our structures show that PetP interacts with the cytoplasmic side of cytb6f, displacing the C-terminus of the PetG subunit and shielding the C-terminus of cytochrome b6, which binds the heme cn cofactor that is suggested to mediate CET. The structures also highlight key differences in the mode of plastoquinone binding between cyanobacterial and plant cytb6f complexes, which we suggest may reflect the unique combination of photosynthetic and respiratory electron transfer in cyanobacterial thylakoid membranes. The structure of cytb6f from a model cyanobacterial species amenable to genetic engineering will enhance future site-directed mutagenesis studies of structure-function relationships in this crucial ET complex., (© 2022 The Author(s).)
- Published
- 2022
- Full Text
- View/download PDF
6. The terminal enzymes of (bacterio)chlorophyll biosynthesis.
- Author
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Proctor MS, Sutherland GA, Canniffe DP, and Hitchcock A
- Abstract
(Bacterio)chlorophylls are modified tetrapyrroles that are used by phototrophic organisms to harvest solar energy, powering the metabolic processes that sustain most of the life on Earth. Biosynthesis of these pigments involves enzymatic modification of the side chains and oxidation state of a porphyrin precursor, modifications that differ by species and alter the absorption properties of the pigments. (Bacterio)chlorophylls are coordinated by proteins that form macromolecular assemblies to absorb light and transfer excitation energy to a special pair of redox-active (bacterio)chlorophyll molecules in the photosynthetic reaction centre. Assembly of these pigment-protein complexes is aided by an isoprenoid moiety esterified to the (bacterio)chlorin macrocycle, which anchors and stabilizes the pigments within their protein scaffolds. The reduction of the isoprenoid 'tail' and its addition to the macrocycle are the final stages in (bacterio)chlorophyll biosynthesis and are catalysed by two enzymes, geranylgeranyl reductase and (bacterio)chlorophyll synthase. These enzymes work in conjunction with photosynthetic complex assembly factors and the membrane biogenesis machinery to synchronize delivery of the pigments to the proteins that coordinate them. In this review, we summarize current understanding of the catalytic mechanism, substrate recognition and regulation of these crucial enzymes and their involvement in thylakoid biogenesis and photosystem repair in oxygenic phototrophs., Competing Interests: The authors declare that there are no competing interests associated with the manuscript., (© 2022 The Authors.)
- Published
- 2022
- Full Text
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