Prosthecochloris aestuarii

The bacteriochlorophyll a protein from the green phot osynthetic bacterium Prosthecochloris aestuarii has been determined at 2.8 A resolution.389 It is made up of three identical subunits, tightly packed around a three-fold symmetry axis. Each subunit consists of a core of seven bacteriochlorophyll a molecules enclosed within a bag of protein. There are extensive contacts between the phytyl chains of the seven bacteriochlorophylls within each subunit. These tails form an inner hydrophobic core. The seven magnesiums appear to be five-coordinate. In five cases the fifth ligand is a histidine side-chain, in one case a protein backbone carbonyl oxygen, and in the other case a water molecule. It appears that the removal of one or more of the bacteriochlorophyll molecules would destabilize the protein. It is unlikely that the chlorophyll can be reversibly removed from the protein. 

Schmidt, K.A., Neerken, S., Permentier, H.P., Hager-Braun, C., and Amesz, J. (2000) Electron transfer in reaction center core complex from green sulfur bacteria Prosthecochloris aestuarii and Chlorobium tepidum, Biochemistry 39, 7212-7220. 

Historically the first X-ray structure [43-45] to undergo exciton analysis was that of the water-soluble BChl a-protein from the green photosynthetic bacterium Prosthecochloris aestuarii. The analysis [16] raised questions, and controversies, that remain unresolved after a decade. It is reviewed again here to emphasize these difficulties, to correct some misconceptions in the literature [4,46,47] regarding possible sources of the difficulties, and to discuss more recent developments. Exciton analysis of photosynthetic pigment-protein complexes is iipt likely to become a truly useful procedure until it produces results that agree with all relevant spectra of this particular complex. 

DETronrud, MF Schmid and BW Mathews (1986) Structure and x-ray amino acid sequence of a bacteriochlo-rophyll a protein from Prosthecochloris aestuarii refined at 1.9 resolution. J Mol Biol 188 443-454 T Katoh, M MImuro and S Takalchl (1989) Light-harvesting particles Isolated from a brown alga, DIctyota dichotoma. A supramolecular assembly of fucoxanthin-chlorophyll-protein complexes. Biochim Biophys Acta 976 233-240... 

Fig. 3. Top row absorption spectra of the 3-FMO/RC-core (A), 1-FMO/RC-core (B) and RC-core (C) complexes. The table lists various spectroscopic properties, chemical compositions, and photochemical activities. Spectra and data from Francke, Permentier, Franken, Neerken and Amesz (1997) Isolation and properties of photochemically active reaction center complexes from the green sulfur bacterium Prosthecochloris aestuarii. Biochemistry 36 14169.

Fig. 4. Light-induced absorbance changes (A) open symbols/solid line for Complex I" solid symbols/dashed line for the PP (ghotosystem-gigment) complex normalized to equal absorbance at 810 nm. (B) both traces for the RCPP (reaction center gigment grotein) complex, but on different AA scales. See text for discussion. Figures from Swarthoff and Amesz (1979) Photo-chemically active pigment-protein complexes from the green photosynthetic bacterium Prosthecochloris aestuarii. Biochim Biophys Acta. 548 p. 430, 431.

Fig. 5. Kinetics of absorbance changes in Complex I of Pc. aestuarii at various waveiengths induced by 532-nm puises of 16-ps duration. See text for details. Figure source Nuijs, Vasmei, Joppe, Duysens and Amesz (1985) Excited states and primary charge separation in the pigment system of the green photosynthetic bacterium Prosthecochloris aestuarii as studied by pico- second absorbance difference spectroscopy. Biochim Biophys Acta 807 30.

Fig. 6. Absorbance changes induced by 33-ps, 850-nm laser pulses in Complex 1 obtained from membranes of the green sulfur bacterium Pc. aestuarff. (A) Membrane with "closed RCs (sample containing FeCy and under background Illumination) (B) membrane with open RCs (sample containing Asc and PMS). Solid-line traces represent absorbance changes observed at the time the excitation flash was applied, and the dotted-line traces are for changes observed at 350 ps after the flash. Figure source Shuvalov, Amesz and Duysens (1986) Picosecond spectroscopy of isolated membranes of the photosynthetic green sulfur bacterium Prosthecochloris aestuarii upon selective excitation of the primary electron donor. Biochim Biophys Acta. 851 2, 3.

T Swarthoff and J Amesz (1979) Photochemically active pigment-protein complexes from the green photosynthetic bacterium Prosthecochloris aestuarii. Biochim Biophys Acta 548 427-432... 

FI Vasmel, T Swarthoff, FIJM Kramer and J Amesz (1983) Isolation and properties of a pigment protein complex associated with the reaction center of the green photosynthetic sulfur bacterium Prosthecochloris aestuarii. Biochim Biophys Acta 725 361-367... 

C Francke, FIP Permentier, EM Franken, S Neerken and J Amesz (1997) Isolation and properties of photochemically active reaction center complexes from the green sulfur bacterium Prosthecochloris aestuarii. Biochemistry 36 14167-14172... 

T Swarthoff, P Gast, AJ Floff and J Amesz (1981) An optical and ESR investigation on the acceptor side ofthe reaction center of the green photosynthetic bacterium Prosthecochloris aestuarii. FEBS Lett 130 93-98... 

P. aestuarii - Prosthecochloris aestuarii ps - picosecond, or 10" second PsaA-N - the polypeptide subunits of photosystem I (see Chapter 1, Table 1 to 6) psaA-N - genes encoding the PsaA-N polypeptide subunits of photosystem I (see Chapter 1, Table 1 to 6)... 

BChl 663 with absorption maxima at 663 and 4-33 nm, like BChl c, was found recently in Prosthecochloris aestuarii by means of reversed-phase HPLC [8], and the presence of this pigment in other species of green sulfur bacteria has not been reported. BChl 663 was assayed at an amount of 10-15 molecules per reaction center and was supposed to be a likely candidate for the primary electron acceptor [8]. In our present study the BChl a/BChl 663 molar ratio is 9 5-11 9 (four independent measurements), where the extinction coefficient of BChl 663 is assumed to be equal to that of BChl c. Although we have not... 

We apply the concept to the bacteriochlorophyll (BCHL) a - protein antenna complex from Prosthecochloris aestuarii. whose structure has been solved by X-ray diffraction and which exhibits a series of low energy absorption maxima at low temperatures that range from 793-825 nm. ... 

The PP and RCPP complexes were prepared from Prosthecochloris aestuarii as earlier described (Swarthoff, Amesz, 1979). Low-temperature spectra were measured in a non-crystallizing medium, obtained by addition of sucrose and glycerol. LD spectra were measured in a polyacrylamide gel, pressed in two perpendicular directions, so that axially symmetric samples were obtained. The increase in length along the orientation axis was by a factor of 1.5. 

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