Photosynthetic reaction center crystallography

The photosynthetic reaction center of a purple bacterium was the first membrane protein structure solved by crystallography. Although a more complex membrane protein than bacteriorhodopsin, it is constructed on the same principles. The reaction center has four protein... 

Hartmut was able to grow crystals of bacteriorhodopsin but they were not suitable for X-ray crystallography for various reasons. He went to scientific meetings where people interested in membrane proteins came together and at one of these meetings he heard about photosynthetic reaction centers and about purification protocols available at that time, and the big advantages that the purple bacteria can provide. Under certain conditions their membranes are filled with photosynthetic reaction centers. Thus you can have a good source of protein, which is extremely important. He tried to work with them and soon he had success. 

Deisenhofer was independent, too. This project was not simple crystallography, not at all. It was a most complex structure determination. Even the methods of measuring the intensities were not automated at the time. We had developed instruments. X-ray cameras and methods for that purpose also. We had a small workshop at that time, with a mechanic and an electronics person. One day the mechanic had a stroke. A week later the electronics person had a heart attack. They were very important in servicing the instruments. I was the only one in my department able to service the instruments. It was at a critical time for the photosynthetic reaction center work, around 1983, and I spent much time each day taking care of the instruments. It is a side issue, not even a scientific one, but it shows you that things may look different from the perspective of today s possibilities than they actually were. The work at that time required a background also concerning the availability of the samples for isomorphous replacement and methods to apply them. I have made many of these samples and I built up an enormous collection. 

Fig. 7. A frame of reference for the Rp. viridis RC-associated cytochrome complex (A) and a more detailed view of the cytochrome subunit with the four hemes shown (B). See text for the various nomenclatures used. P represents the [BChllj (the primary donor). The table also includes the redox-potential values of the hemes, and the wavelength of the a-band of the hemes both at room and cryogenic temperatures. Figure (A) the same as Fig. 7 in Chapter 2. (B) is taken from CRD Lancaster, U Ermler and H Michel (1995) The structure of photosynthetic reaction centers from purple bacteria as revealed by X-ray crystallography. In RE Blankenship, MT Madigan and CE Bauer (eds) Anoxygenic Photosysnthetic Bacteria, p 511. Kluwer.

Lancaster, C. R. D. Ermler, U. Michel, H. "The Structures of Photosynthetic Reaction Centers from Purple Bacteria as Revealed by X-ray Crystallography," in Anoxygenic Photosynthetic Bacteria Blankenship, R. E., Madigan, M. T. and Bauer, C. E., Ed. Kluwer Dordrecht, 1995, pp 503-526 and references thoein. 

Lancaster CRD, ErmlerU and Michel H (1995) The structures of photosynthetic reaction centers from purple bacteria as revealed by X-ray crystallography. In Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 503-526. Kluwer Academic Publishers, Dordrecht Lancaster CRD, Michel H, Honig B and Gunner MR (1996) Calculated coupling of electron and proton transfer in the photosyntheticreaction centre of Rhodopseudomonas viridis. Biophys 1 70 2469-2492... 

Carotenoids function in photosynthetic reaction centers (RC) as triplet quenchers of the primary donor chlorophyll or bacteriochlorophyll triplet states. The best studied RCs are those of purple photosynthetic bacteria where atomic models are available based on X-ray crystallography and optical as well as magnetic resonance spectroscopies have yielded a detailed picture of the flow of triplet energy transfer. Good reviews of these topics can be found in (Frank, 1992, 1993 Frank and Cogdell, 1996). 

Light-induced electron transport in bacterial photosynthetic reaction centers leads to the creation of a charge-separated state stable for milliseconds to seconds. The structures provided by X-ray crystallography (Michel et aL, 1986 Allen et al., 1988 Deisenhofer Michel, 1989 El-Kabbani et al., 1991) constitute a unique guideline to address questions on how the function may be related to the arrangement of the cofactors and of specific amino acid residues in their vicinity. The sequence of electron transfer reactions, the identity of the reaction partners, and the reaction mechanisms have been characterized from static and time-resolved absorbance measurements (for a review, see Parson Ke, 1982). Transfer of the first electron to the primary (Q ) and secondary (Qg) quinone electron acceptors has received considerable attention, since it is associated with intraprotein protolytic reactions (for a recent review, see Okamura Feher, 1992), which have a potential role in electrostatic charge stabilization. 

Organized molecular assemblies containing redox chromophores show specific and useful photoresponses which cannot be achieved in randomly dispersed systems. Ideal examples of such highly functional molecular assemblies can be found in nature as photosynthesis and vision. Recently the very precise and elegant molecular arrangements of the reaction center of photosynthetic bacteria was revealed by the X-ray crystallography [1]. The first step, the photoinduced electron transfer from photoreaction center chlorophyll dimer (a special pair) to pheophytin (a chlorophyll monomer without... 

Deisenhofer, J., and H. Michel, The photosynthetic reaction centre from the purple bacterium Rhodopseudomonas viridis. Science 245 1463, 1989. The structure of abacterial reaction center is revealed by x-ray crystallography. 

The Nobel Prize in chemistry was awarded to Johan Deisenhofer, Robert Huber, and Hartmut Michel in 1988 for unraveling the structure of the reaction center from the purple photosynthetic bacterium Rhodopseudomonas viridis using X-ray crystallography. 

The NATO Advanced Research Workshop entitled "The Photosynthetic Bacterial Reaction Center Structure, Spectroscopy, and Dynamics" was held May 10-15, 1992, in the Maison d Hotes of the Centre d Etudes Nucleaires de Cadarache near Aix-en-Provence in the south of France. This workshop is the most recent of a string of meetings which started in Feldafing (Germany) in March 1985, soon after the three-dimensional structure of the bacterial reaction center had been elucidated by X-ray crystallography. This was followed, in September 1987, by a workshop in Cadarache and, in March 1990, by a second meeting in Feldafing. 

Cytochrome C2 from Rhodospirillitan rubrum, a photosynthetic bacterium, is closely analogous in amino acid sequence and three dimensional structure to the soluble c-type cytochromes of eukaryotic species. X-ray crystallography studies have clearly established histidine and methionine as axial ligands to the heme group (Salemme et ai, 1973). Cytochrome C2 is thought to be the primary electron donor to the photosynthetic light reaction center. A number of studies have shown that the active site environment of this protein is similar to that of eurkaryotic cytochrome c. 

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