Photosynthetic bacteria reaction center structure

P. Parot, J. Thiery and A. Verm glio, Charge recombination at low temperature in photosynthetic bacteria reaction centers, in "The Photosynthetic Bacterial Reaction Center Structure and dynamics" 251, J. Breton and A. Verm glio eds.. Plenum Publishing Corporation, New-York-London (1988). 

Fig. 2. (A) SDS-PAGE electrophoresis showing the polypeptide subunits of the reaction-center of Rb. sphaeroides R-26 (B) and (C) SDS-PAGE electrophoresis patterns of the LM-complex and the H-subunit obtained by treating the reaction center with SDS/ LDAO followed by centrifugation in a sucrose-density gradient. Figure from Okamura, Steiner and Feher (1974) Characterization of reaction centers from photosynthetic bacteria. I. Subunit structure of the protein mediating the primary photochemistry in Rhodopseudomonas sphaeroides R-26. Biochemistry, 13 137, 138.

We now summarize in Fig. 11 the reaction-center structure and the known electron-transport reactions in purple bacteria. A simplified representation of the reaction-center and the light-harvesting complexes contained in the bacterial membrane is shown in Fig. 11 (A), followed by a column model and a cofactor model in Fig. 11 (B). The cofactor model is used to illustrate the various electron-transport steps with the associated rate constants in Fig. 11 (C), where the cofactors in the starting state (oxidized or reduced) are shown in solid black. When a cofactor first becomes reduced or oxidized, it is shown as an open symbol. We will also use this cofactor model and reaction sequence as a framework for introducing the remaining chapters throughout the section on photosynthetic bacteria. 

J. L. Martin, J. Breton, J. C. Lambry, and G. Fleming. The primary electron transfer in photosynthetic purple bacteria Long range electron transfer in the femtosecond domain at low temperature. In J. Breton and A. Vermeglio, editors. The Photo synthetic Bacterial Reaction Center Structure and Dynamics, pages 195-203, New York and London, 1988. Plenum Press. 

Vos M H, Jones M R, Hunter C N, Breton J, Lambry J C and Martin J L 1996 Femtosecond spectroscopy and vibrational coherence of membrane-bound RCs of Rhodobacfe/ sp/raero/des genetically modified at positions M210 and LI 81 The Reaction Center of Photosynthetic Bacteria—Structure and Dynamics ed M E Michel-Beyerle (Berlin Springer) pp 271-80... 

Despite considerable efforts very few membrane proteins have yielded crystals that diffract x-rays to high resolution. In fact, only about a dozen such proteins are currently known, among which are porins (which are outer membrane proteins from bacteria), the enzymes cytochrome c oxidase and prostaglandin synthase, and the light-harvesting complexes and photosynthetic reaction centers involved in photosynthesis. In contrast, many other membrane proteins have yielded small crystals that diffract poorly, or not at all, using conventional x-ray sources. However, using the most advanced synchrotron sources (see Chapter 18) it is now possible to determine x-ray structures from protein crystals as small as 20 pm wide which will permit more membrane protein structures to be elucidated. 

Michel, H., Deisenhofer, J. Relevance of the photosynthetic reaction center from purple bacteria to the structure of photosystem II. BicKhemistry 27 1-7, 1988. 

The photosynthetic reaction center (RC) of purple nonsulfur bacteria is the core molecular assembly, located in a membrane of the bacteria, that initiates a series of electron transfer reactions subsequent to energy transfer events. The bacterial photosynthetic RCs have been characterized in more detail, both structurally and functionally, than have other transmembrane protein complexes [1-52]. 

M. E. Michel-Beyerle, The Reaction Center of Photosynthetic Bacteria Structure and Dynamics, Springer, Berlin, 1996. 

Antennas and Reaction Centers of Photosynthetic Bacteria. Structure, Interactions and Dynamics" Michel-Beyerle, M. E., Ed. Springer-Verlag, Berlin, 1985. 

Deisenhofer, J. Michel, H. (1991) Structures of bacterial photosynthetic reaction centers. Annu. Rev. Cell Biol. 7, 1-23. Description of the structure of the reaction center of purple bacteria and implications for the function of bacterial and plant reaction centers. 

Many cytochromes c are soluble but others are bound to membranes or to other proteins. A well-studied tetraheme protein binds to the reaction centers of many purple and green bacteria and transfers electrons to those photosynthetic centers.118 120 Cytochrome c2 plays a similar role in Rhodobacter, forming a complex of known three-dimensional structure.121 Additional cytochromes participate in both cyclic and noncyclic electron transport in photosynthetic bacteria and algae (see Chapter 23).120,122 124 Some bacterial membranes as well as those of mitochondria contain a cytochrome bct complex whose structure is shown in Fig. 18-8.125,126... 

Very few integral membrane proteins have been crystallized. The reaction-center proteins purified from membranes of photosynthetic bacteria are a notable exception. These proteins were discussed in chapter 15. Before their crystal structures were elucidated, analysis of hydropathy plots suggested that each of the two main protein subunits is folded into five transmembrane a helices, and one such helix was predicted to occur in another subunit. The crystal structures provided a beautiful confirmation of these predictions (see fig. 15.11a). Successful crystallization of the reaction-center proteins was achieved by including small,... 

The results of this study demonstrate that the antenna and the reaction center of R rubrum differ in then-specificities of carotenoid binding. Thus, the microorganism follows in this respect the pattern of other related phototrophic bacteria (Cogdell and Thomber, 1979 Cogdell et al., 1976). Such difference suggests strongly that the functional role of the carotenoid in each type of photosynthetic complex has differential aspects of importance sufficient to impose distinctive structural requirements. The available information on... 

Likhtenshtein, G.I., Kulikov, A.V., Kotelnikov, A.I. and Bogatyrenko V.R. (1982) Structure and action mechanism of reaction centers of photosynthetic bacteria. Photobiochem. Photobiol. 3, 178-182. Likhtenshtein, G.I., Kulikov, A. V., Kotelnikov, A.I., and Levchenko, L.A. (1986) Methods ofphysical labels -a combined approach to the study of microstructure and dynamics of biological systems. J. Biochem. Biophys. Meth. 12, 1-28. 

Since the first isolation of a reaction center preparation from the membrane of a facultative photosynthetic bacterium [6] our knowledge on the structure and function of these complexes has made great advances. Today the RC from purple bacteria, and particularly from the carotenoid-less strain R26 of Rhodopseudomonas sphaeroides, are by far the best known examples of photosynthetic complexes studied. Other RC from different bacteria species have also been studied and differences in components sometimes observed these differences will be mentioned below, whenever necessary, while discussing the properties of the preparations from Rp. sphaeroides R26. 

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