On the role of tryptophan as a superexchange mediator for quinone reduction in photosynthetic reaction centers

Plato, M.; Michel‐Beyerle, M. E.; Bixon, M.; Jortner, J.

doi:10.1016/0014-5793(89)80018-3

Cited by 58 publications

(31 citation statements)

References 23 publications

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“…Hence, it most probably reflects an enhanced -electron coupling provided by the additional aromatic residue [19] and further supporting the notion of an optimal "Trp48 ET pathway". Indeed, aromatic residues are often found in positions where they may enhance the electronic coupling between ET donor and acceptor in several systems probably selected by evolution for efficient electron transfer [19][20][21][22].…”

Section: Azurinsmentioning

confidence: 99%

Electron transfer in blue copper proteins

Farver

Pecht

2011

Coordination Chemistry Reviews

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Section: Azurinsmentioning

confidence: 99%

Electron transfer in blue copper proteins

Farver

Pecht

2011

Coordination Chemistry Reviews

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“…An aromatic residue D2-W253 is found to be located between the QA head group and the "active" pheophytin and is separated from the porphyrin by 3.1 8, and from the QA by 3.7 A. This residue has been suggested to be a "superexchange" mediator for the electron transport between pheophytin and plastoquinone (Plato et al, 1989). Another residue in between the same pheophytin and QA is D2-1213, which is positioned 4.5 A from the porphyrin of pheophytin and 4.7 8, from the head group of QA, and may play a role similar to D2-W253.…”

Section: Pheophytinsmentioning

confidence: 99%

Modeling of the D1/D2 proteins and cofactors of the photosystem II reaction center: Implications for herbicide and bicarbonate binding

1996

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A three-dimensional model of the photosystem I1 (PSII) reaction center from the cyanobacterium Synechocystis sp. PCC 6803 was generated based on homology with the anoxygenic purple bacterial photosynthetic reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis, for which the X-ray crystallographic structures are available. The model was constructed with an alignment of Dl and D2 sequences with the L and M subunits of the bacterial reaction center, respectively, and by using as a scaffold the structurally conserved regions (SCRs) from bacterial templates. The structurally variant regions were built using a novel sequence-specific approach of searching for the best-matched protein segments in the Protein Data Bank with the "basic local alignment search tool" (Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ, 1990, J Mol Biol 215:403-410). and imposing the matching conformational preference on the corresponding D l and D2 regions. The structure thus obtained was refined by energy minimization. The modeled D l and D2 proteins contain five transmembrane a-helices each, with cofactors (4 chlorophylls, 2 pheophytins, 2 plastoquinones, and a non-heme iron) essential for PSII primary photochemistry embedded in them. A p-carotene, considered important for PSII photoprotection, was also included in the model. Four different possible conformations of the primary electron donor P680 chlorophylls were proposed, one based on the homology with the bacterial template and the other three on existing experimental suggestions in literature. The P680 conformation based on homology was preferred because it has the lowest energy.Redox active tyrosine residues important for P680' reduction as well as residues important for PSI1 cofactor binding were analyzed. Residues involved in interprotein interactions in the model were also identified. Herbicide 3-(3,4-dichlorophenyI)-I , 1 -dimethylurea (DCMU) was also modeled in the plastoquinone QB binding niche using the structural information available from a DCMU-binding bacterial reaction center.A bicarbonate anion, known to play a role in PSII, but not in anoxygenic photosynthetic bacteria, was modeled in the non-heme iron site, providing a bidentate ligand to the iron. By modifying the previous hypothesis of Blubaugh and Govindjee (1988, Photosyn Res 1 9 3 -1 2 8 ) , we modeled a second bicarbonate and a water molecule in the Qe site and we proposed a hypothesis to explain the mechanism of QB protonation mediated by bicarbonate and water. The bicarbonate, stabilized by DLR257, donates a proton to Qi-through the intermediate of DLH252; and a water molecule donates another proton to Qi-. Based on the discovery of a "water transport channel" in the bacterial reaction center, an analogous channel for transporting water and bicarbonate is proposed in our PSII model. The putative channel appears to be primarily positively charged near QB and the non-heme iron, in contrast to the polarity distribution in the bacterial water transport channel. The constructed model has ...

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“…sphaeroides (1)(2)(3)(4). The indole ring of the tryptophan M252 is in van der Waals contact with both the bacteriopheophytin HA and the quinone QA and was suspected from this unique position to participate as a (superexchange) mediator in electron transfer (5). At the same time tryptophan M252 may contribute via a charge transfer interaction to the binding of quinone to the QA site (6).…”

Section: Introductionmentioning

confidence: 98%