Bacteriochlorophyll-protein complex structure

Prince SM, Papiz, MZ, Freer AA, McDermott G, Hawthornthwaite-Lawless AM, Cogdell RJ and Isaacs NW (1977) Apoprotein structure in the LH2 complex from Rhodopseudomonas acidophila strain 10050 Modular assembly and protein pigment interactions. J Mol Biol 268 412-423 Pullerits T and Sundstrom V (1996) Photosynthetic lightharvesting pigment-protein complexes Toward understanding how and why. Acc Chem Res 29 381-389 Robert B and Lutz M (1985) Structure of anterma complexes of several Rhodospirillales from their resonance Raman spectra. Biochim Biophys Acta 807 10-23 Sauer K, Cogdell RJ, Prince SM, Freer AA, Isaacs NW and Scheer H (1996) Structure based calculations ofthe optical spectra ofthe LH2 bacteriochlorophyll-protein complex from Rhodopseudomonas acidophila. Photochem Photobiol 64 564-576... 

Reaction centers of purple bacteria. The exact composition varies, but the properties of reaction centers from several genera of purple bacteria are similar. In Rhodopseudomonas viridis there are three peptide chains designated H, M, and L (for heavy, medium and light) with molecular masses of 33,28, and 24 kDa, respectively. Together with a 38-kDa tetraheme cytochrome (which is absent from isolated reaction centers of other species) they form a 1 1 1 1 complex. This constitutes reaction center P870. The three-dimensional structure of this entire complex has been determined to 0.23-nm resolution288 319 323 (Fig. 23-31). In addition to the 1182 amino acid residues there are four molecules of bacteriochlorophyll (BChl), two of bacteriopheophytin (BPh), a molecule of menaquinone-9, an atom of nonheme iron, and four molecules of heme in the c type cytochrome. In 1984, when the structure was determined by Deisenhofer and Michel, this was the largest and most complex object whose atomic structure had been described. It was also one of the first known structures for a membrane protein. The accomplishment spurred an enormous rush of new photosynthesis research, only a tiny fraction of which can be mentioned here. 

Another antenna complex where high-resolution structural information is available is the bacteriochlorophyll a binding protein (also known as the Fenna-Matthews-Olson or FMO protein) from green sulfur bacteria. This complex serves as the bridge between the peripheral chlorosome complex and the membrane-bound reaction center complexes. In this... 

The basic structure of aU the component proteins making up the Light-harvesting (LH) complexes of purple photosynthetic bacteria is similar." " It consists of two polypeptides a- and jS-subunits) that fold into transmembrane Q -hehces and form a heterodimer that noncovalently binds bacteriochlorophyll... 

Figure 20.34 shows the reaction center of the related bacterium R. sphaeroides its structure is much more evident when the surrounding protein is stripped away. This complex consists of four bacteriochlorophyll molecules (the special pair and two others), two bacteriopheophytin molecules (which are bacteriochlorophyll molecules in which the central Mg ion is replaced by two hydrogen ions), two ubiquinone molecules (Fig. 20.35), and an iron(II) ion. Interestingly, these... 

The photosynthetic reaction centres (RCs) are transmembrane protein-pigment complexes that perform light-induced charge separation during the primary steps of photosynthesis. RCs from purple bacteria consist of three protein subunits, L, M and H, and bind four bacteriochlorophylls, two bacteriopheophytins, two quinones, one non-haem iron and one carotenoid. The elucidation at atomic resolution of the three-dimensional structures of the bacterial RCs from Rhodopseudomonas (Rps.) viridis (1) and Rhodobacter (Rb,) sphaeroides (2-4) has provided impetus for theoretical and experimental work on the mechanism of primary charge separation in the RCs. The structures revealed that the cofactors are bound at the interface between the L and M subunits and are organised around a pseudo C2 symmetry axis. However, the structural symmetry does not result in functional symmetry as the electron transfer proceeds only along the L branch (5). 

In addition to the 1182 amino acid residues there are four molecules of bacteriochlorophyll (BChl), two of bacteriopheophytin (BPh), a molecule of menaquinone-9, an atom of nonheme iron, and four molecules of heme in the c type cytochrome. In 1984, when the structure was determined by Deisenhofer and Michel, this was the largest and most complex object whose atomic structure had been described. It was also one of the first knovm structures for a membrane protein. The accomplishment spurred an enormous rush of new photosynthesis research, only a tiny fraction of which can be mentioned here. 

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