Photosynthetic architecture

Strzepek RF and Harrison PJ (2004) Photosynthetic architecture differs in coastal and oceanic diatoms. Nature 431 689-692. 

Traditionally, the electron and proton transport pathways of photosynthetic membranes (33) have been represented as a "Z" rotated 90° to the left with noncycHc electron flow from left to right and PSII on the left-most and PSI on the right-most vertical in that orientation (25,34). Other orientations and more complex graphical representations have been used to depict electron transport (29) or the sequence and redox midpoint potentials of the electron carriers. As elucidation of photosynthetic membrane architecture and electron pathways has progressed, PSI has come to be placed on the left as the "Z" convention is being abandoned. Figure 1 describes the orientation in the thylakoid membrane of the components of PSI and PSII with noncycHc electron flow from right to left. 

What molecular architecture couples the absorption of light energy to rapid electron-transfer events, in turn coupling these e transfers to proton translocations so that ATP synthesis is possible Part of the answer to this question lies in the membrane-associated nature of the photosystems. Membrane proteins have been difficult to study due to their insolubility in the usual aqueous solvents employed in protein biochemistry. A major breakthrough occurred in 1984 when Johann Deisenhofer, Hartmut Michel, and Robert Huber reported the first X-ray crystallographic analysis of a membrane protein. To the great benefit of photosynthesis research, this protein was the reaction center from the photosynthetic purple bacterium Rhodopseudomonas viridis. This research earned these three scientists the 1984 Nobel Prize in chemistry. 

Ferreira, K.N., Iverson, T.M., Maghlaoui, K., Barber, J. and Iwata, S., (2004). Architecture of the photosynthetic oxygen-evolving center. Science, 303, 1831-1838... 

Schulten, K. (ed.) (1999). In From Simplicity to Complexity and Back. Function, Architecture, and Mechanism of Light-Harvesting Systems in Photosynthetic Systems. Simplicity and Complexity in Proteins and Nucleic Acids. Dahlem University Press. 

The (a-SS-a)2 architecture of Robertson et al. has shown wide utility as a basis structure in the systematic design of ever more sophisticated metalloprotein maquettes of the photosynthetic 36) and respiratory complexes toward the goal of testing the fundamentals of biological... 

Until a recent x-ray diffraction study (17) provided direct evidence of the arrangement of the pigment species in the reaction center of the photosynthetic bacterium Rhodopseudomonas Viridis, a considerable amount of all evidence pertaining to the internal molecular architecture of plant or bacterial reaction centers was inferred from the results of in vitro spectroscopic experiments and from work on model systems (5, 18, 19). Aside from their use as indirect probes of the structure and function of plant and bacterial reaction centers, model studies have also provided insights into the development of potential biomimetic solar energy conversion systems. In this regard, the work of Netzel and co-workers (20-22) is particularly noteworthy, and in addition, is quite relevant to the material discussed at this conference. 

The first issue can be addressed in two ways a primary ET species which has a large optical absorption cross-section can be chosen or arrays of molecules with large optical absorption cross-sections can be used as "antennas" that will efficiently collect and transport the electronic excitation energy to the primary ET species, in direct analogy to photosynthetic systems. While in the latter case it should be possible to develop systems with more efficient solar photon collection, the number of primary ET species will have to be reduced due to the spatial limitations, which will also reduce the potential electric current that can be produced by the system. Thus, questions related to the detailed molecular architecture of biomimetic solar energy conversion devices will have to address this issue, and it is quite likely that a number of compromises will have to be made before optimal design characteristics are obtained. 

Ferreira KN et al (2004) Architecture of the photosynthetic oxygen-evolving center. Science... 

This work > is of importance in relevant to the water oxidation reaction in the photosynthetic membrane. The oxidation of two water molecules to evolve dioxygen in photosystem II is understood to be realized by an enzymatic organization of a special Mn cluster in a protein architecture This oxygen... 

C.A. Siebert, P. Qian, D. Fotiadis, A. Engel, C.N. Hunter, P.A. BuUough, Molecular architecture of photosynthetic membranes in Rhodobacter sphaeroides the Role of Pufx. EMBO J. 23, 690-700 (2004)... 

Fullerene-porphyrin architectures as photosynthetic antenna and reaction center models 02CSR22. 

DJ Lundell, RC Williams and AN Glazer (1981) Molecular architecture of a light-harvesting antenna. In vitro assembly of the rod substructures of Synechococcus 6301 phycobilisomes. J Biol Chem 256 3580-3592 S Brody and E Rabinowitch (1957) Excitation lifetime of photosynthetic pigments. Science 125 555 G Tomita and E Rabinowitch (1962) Excitation energy transfer between pigments in photosynthetic cells. Biophys J 2 483-499... 

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