Factors that determine the unusually low reduction potential of cytochrome c 550 in cyanobacterial photosystem II

Vrettos, John S.; Reifler, Michael J.; Kievit, Olaf; Lakshmi, K. V.; Paula, Julio C. de; Brudvig, Gary W.

doi:10.1007/s007750100249

Cited by 31 publications

(42 citation statements)

References 52 publications

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“…compatible with the model predicted theoretically (38) or that analyzed by single-particle analysis of cryoelectron microscopic images from higher plants (39). The structure of cyt c550 was modeled partially with the help of the recently reported structure of this cyt from two other cyanobacteria (40,41), generating a structure very similar to those from the other cyanobacteria. The newly assigned 12-kDa protein has an all-␣ architecture composed of five or more short ␣-helices, with no homologous structure in the database.…”

Section: Resultssupporting

confidence: 56%

Crystal structure of oxygen-evolving photosystem II fromThermosynechococcus vulcanusat 3.7-Å resolution

Kamiya

Shen

2002

Proc. Natl. Acad. Sci. U.S.A.

1,111

840

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To analyze the PSII structure in more detail, we have obtained the crystal structure of PSII from another thermophilic cyanobacterium, Thermosynechococcus vulcanus, at 3.7-Å resolution. The present structure was built on the basis of the sequences of PSII large subunits D1, D2, CP47, and CP43; extrinsic 33-and 12-kDa proteins and cytochrome c550; and several low molecular mass subunits, among which the structure of the 12-kDa protein was not reported previously. This yielded much information concerning the molecular interactions within this large protein complex. We also show the arrangement of chlorophylls and cofactors, including two ␤-carotenes recently identified in a region close to the reaction center, which provided important clues to the secondary electron transfer pathways around the reaction center. Furthermore, possible ligands for the Mn-cluster were determined. In particular, the C terminus of D1 polypeptide was shown to be connected to the Mn cluster directly. The structural information obtained here provides important insights into the mechanism of PSII reactions.T he photosystem II (PSII) complex is a multisubunit membrane-protein complex consisting of Ͼ14 membranespanning subunits, 3 hydrophilic peripheral subunits, and Ͼ40 cofactors, including chlorophylls (chls), carotenoids, Mn, Fe, and plastoquinones, with a total molecular mass of 320 kDa for a monomer (for review, see refs. 1-3). The PSII reaction center (RC) P680 is a (pair of) chl a coordinated by RC D1- and undergoes charge separation on absorption of light energy; the electrons thus generated are transferred to pheophytin, the first quinone acceptor Q A , and then the second quinone acceptor Q B . At the oxidizing side of PSII, a redoxactive tyrosine residue D1-Tyr-161 (Tyr Z ) reduces P680. The oxidized Tyr Z withdraws electrons from a Mn cluster consisting of four Mn atoms, which in turn withdraws electrons in a sequential way from water molecules, leading to the splitting of water and formation of molecular oxygen. This reaction provides us with the oxygen-rich atmospheric environment suitable for most of the organisms to live on the earth, whereas the protons yielded are the source for proton gradient across the thylakoid membrane required for ATP formation.In view of its importance, PSII has received extensive studies in the past several decades regarding its protein composition, function, and dynamic regulation. As a result, our understanding of the function and reaction mechanisms of PSII has increased greatly. However, studies of the structure of PSII have appeared only in recent years. The 3D image of PSII was first studied by electron cryomicroscopy of 2D crystals of various PSII particles, and a structure at 8-Å resolution has been reported for a CP47-RC-PSII complex, which lacked oxygen-evolving activity, and its related three extrinsic proteins (4, 5). Recently, 3D crystals have been obtained for oxygen-evolving PSII complexes from two species of thermophilic cyanobacteria (6-8), and the PSII crystal structure from one of...

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Section: Resultssupporting

confidence: 56%

Crystal structure of oxygen-evolving photosystem II fromThermosynechococcus vulcanusat 3.7-Å resolution

Kamiya

Shen

2002

Proc. Natl. Acad. Sci. U.S.A.

1,111

840

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“…The difference of E m between the isolated and the PSII-bound forms of cyt c 550 has been confirmed by theoretical calculations based on crystal structures of the isolated and PSII-bound forms (25). Some authors (13,24,26) have proposed that in conditions more native than isolated PSII core complexes, it is possible that the E m of cyt c 550 may be even higher than Ϫ80 mV, and thus a redox function in the water oxidation complex could be conceivable. Therefore, the precise determination of the redox potential of this protein is of fundamental importance to the understanding its function.…”

mentioning

confidence: 61%

“…PCC 6803 (9), Arthrospira maxima (10), and Thermosynechococcus elongatus (11) has confirmed a previously proposed bis-histidine coordinated heme that is very unusual for monoheme c-type cytochromes (8,11,12). Crystal structures of both isolated and PSII-bound forms of cyt c 550 show that the protein presents a hydrophobic inner core typical of monoheme cytochromes c, with three helices forming a nest for the prosthetic group and a fourth helical segment in the N-terminal domain protecting the heme from solvent, indicating that the heme structure is not very different from most c-type cytochromes (13).…”

mentioning

confidence: 99%

“…Using an electrochemical technique, a value 150 mV more positive (E m7 Ϸ Ϫ100 mV) was measured for E m of cyt c 550 from Synechocystis sp. PCC 6803 adsorbed to an electrode surface (13). This higher value was attributed to the exclusion of water from the site due to the protein binding to the electrode (13).…”

mentioning

confidence: 99%

“…PCC 6803 adsorbed to an electrode surface (13). This higher value was attributed to the exclusion of water from the site due to the protein binding to the electrode (13). The E m for cyt c 550 associated with PSII was not established until our group was able to measure it using intact PSII core complexes preparations from T. elongatus.…”

mentioning

confidence: 99%

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A High Redox Potential Form of Cytochrome c550 in Photosystem II from Thermosynechococcus elongatus

Guerrero

Sedoud

Kirilovsky

et al. 2011

Journal of Biological Chemistry

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Cytochrome c 550 (cyt c 550 ) is a component of photosystem II (PSII) from cyanobacteria, red algae, and some other eukaryotic algae. Its physiological role remains unclear. In the present work, measurements of the midpoint redox potential (E m ) were performed using intact PSII core complexes preparations from a histidine-tagged PSII mutant strain of the thermophilic cyanobacterium Thermosynechococcus (T.) elongatus. When redox titrations were done in the absence of redox mediators, an E m value of ؉200 mV was obtained for cyt c 550 . This value is ϳ300 mV more positive than that previously measured in the presence of mediators (E m ‫؍‬ ؊80 mV). The shift from the high potential form (E m ‫؍‬ ؉200 mV) to the low potential form (E m ‫؍‬ ؊80 mV) of cyt c 550 is attributed to conformational changes, triggered by the reduction of a component of PSII that is sequestered and out of equilibrium with the medium, most likely the Mn 4 Ca cluster. This reduction can occur when reduced low potential redox mediators are present or under highly reducing conditions even in the absence of mediators. Based on these observations, it is suggested that the E m of ؉200 mV obtained without mediators could be the physiological redox potential of the cyt c 550 in PSII. This value opens the possibility of a redox function for cyt c 550 in PSII.In all photosynthetic oxygen-evolving organisms, the primary steps of light conversion take place in a large pigmentprotein complex named PSII, 2 which drives light-induced electron transfer from water to plastoquinone with the concomitant production of molecular oxygen (for review, see Ref.1). The reaction center of PSII is made up of two membranespanning polypeptides, D1 and D2, which bind four chlorophylls, two pheophytins, two quinones, Q A and Q B (the primary and secondary quinone acceptors of the reaction centre of PSII), a non-heme iron atom, and a cluster made up of four manganese ions and one calcium ion. In green algae and higher plants, three extrinsic proteins are associated to reaction center in water-splitting active PSII complexes: 23-24, 16 -18, and 33 kDa proteins, whereas in cyanobacteria, red algae and some other eukaryotic algae, cyt c 550 , 12 kDa and 33 kDa proteins are found. The three-dimensional structure of PSII confirmed that cyt c 550 binds on the lumenal membrane surface in the vicinity of the D1 and CP43 (2-6).Cyt c 550 , encoded by the psbV gene, is a monoheme protein with a molecular mass of Ϸ 15 kDa and an isoelectric point between 3.8 and 5.0 (7, 8). The recent resolution of the threedimensional structure of the soluble form of cyt c 550 from three cyanobacteria, Synechocystis sp. PCC 6803 (9), Arthrospira maxima (10), and Thermosynechococcus elongatus (11) has confirmed a previously proposed bis-histidine coordinated heme that is very unusual for monoheme c-type cytochromes (8,11,12). Crystal structures of both isolated and PSII-bound forms of cyt c 550 show that the protein presents a hydrophobic inner core typical of monoheme cytochromes c, with three helices...

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Metal Ions in Cyanobacterial PhotosystemII

Loll

Biesiadka

2004

Handbook of Metalloproteins

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Development of oxygenic photosynthesis provided the primeval reducing atmosphere with oxygen that is essential for all presently existing higher forms of heterotrophic life including human beings. Oxygenic photosynthesis is initiated at photosystem II (PSII), a multi‐subunit protein complex that is decorated with various cofactors and located in the thylakoid membrane of cyanobacteria, algae and higher plants. PSII captures sunlight with its antenna proteins and converts it to chemical energy by catalyzing water oxidation to atmospheric oxygen, protons and electrons. The reducing electrons are exploited in subsequent steps in the formation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) used to reduce CO 2 to carbohydrates. We discuss here the presently most complete structure of cyanobacterial PSII that includes 35 chlorophyll a , 11 carotenoids, 2 pheophytins a , 2 plastoquinones, 2 hemes, bicarbonate, 14 lipids, 3 detergent molecules ( n ‐dodecyl‐β‐ D ‐maltoside), 4 Mn‐atoms, 2 Ca 2+ , and Fe 2+ that are embedded within 19 protein subunits per monomer. Water oxidation takes place at a redox‐active metal cluster that is composed of 4 Mn‐cations and 1 Ca 2+ cation. The arrangement, geometry and coordination of the metal ions in the Mn 4 Ca‐cluster provide information essential for understanding mechanistic aspects of water oxidation.

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Factors that determine the unusually low reduction potential of cytochrome c 550 in cyanobacterial photosystem II

Cited by 31 publications

References 52 publications

Crystal structure of oxygen-evolving photosystem II fromThermosynechococcus vulcanusat 3.7-Å resolution

Crystal structure of oxygen-evolving photosystem II fromThermosynechococcus vulcanusat 3.7-Å resolution

A High Redox Potential Form of Cytochrome c550 in Photosystem II from Thermosynechococcus elongatus

Metal Ions in Cyanobacterial PhotosystemII

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