The photochemical reaction center of Chloroflexus aurantiacus is composed of two structurally similar polypeptides

Abstract

A method has been devised which allowed the isolation of highly purified reaction center from the thermophilic green bacterium, Chlorojlexus aurantiacus. The procedure consisted of three chromatography steps. The final step was fast protein liquid chromatography on Mono Q in the presence of nonanoyl-N-methylglucamide (Mega-9). The purified reaction center complex was photochemically active and had an A280/A813 of 1.4 or less. Under non-denaturing conditions, a pigmented protein band having a M , of 52000 -55000 was observed in sodium dodecyl sulfate gels. When the isolated complex was heat-dissociated in the presence of sodium dodecyl sulfate, just two polypeptides having very similar M , (24000 and 24500) were observed. Two protein bands were also observed in two-dimensional isoelectric focusing/sodium-dodecyl-sulfate polyacrylamide gel electropheresis ; the PI values of the two polypeptides were 6.5 and 6.7. Partial peptide mapping of the two isolated subunits, using both enzymatic and chemical cleavage techniques, yielded almost identical patterns which indicated a high degree of sequence homology between the two polypeptides.The N-terminal amino acid sequences of the two polypeptides were identical and did not exhibit any homology to reaction center subunits of purple sulfur bacteria.The Chlorojlexus reaction center is believed to be composed of one molecule of each polypeptide, the photoactive bacteriochlorophyll a dimer and, as accessory pigments, an additional bacteriochlorophyll a and three bacteriopheophytins. Hence, it appears to be the smallest photochemically active reaction center isolated to date.The first steps of photosynthesis, the conversion of light energy into chemical energy, occours within pigment-protein complexes called reaction centers. The reaction center of several photosynthetic bacteria, primarily belonging to the family Rhodospirillaceae, have been isolated and biochemically characterized. Most reaction center complexes are comprised of three polypeptides having apparent M , = 28 000, 24000 and 21 000 as determined by NaDodS0,-PAGE. The polypeptides are present in the complex in a 1 : 1 : 1 molar stoichiometry. The reaction center from Rps. viridis contains an additional four heme cytochrome subunits ( M , 40000). Non-covalently bound to the protein moiety are four bacteriochlorophylls, two bacteriopheophytins, one to two quinones and non-heme iron (for reviews, see [I, 21). The recent success in crystallizing reaction center from Rps. viridis and the subsequent X-ray diffraction analysis has led to a three-dimensional molecular model of this pigment-protein [3, 41. Extensive optical and time-resolved spectroscopical analyses have revealed the primary photochemical electron-transfer steps in isolated reaction centers. While there is general agreement on the 'late' photochemical processes (> lo-" s), there are conflicting data on the late femtoseconds to early picoseconds events [5 -1 I].The subcellular organization and location of the components of the photosynthetic apparatus and t...

Temperature dependence of charge recombination from the P+QA− and P+QB− states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus

“…The C ' Z . aurantiacus RC was isolated and purified as previously described by Shiozawa et al [32].…”

Structural and Spectroscopic Properties of a Reaction Center Complex from the Chlorosome-Lacking Filamentous Anoxygenic Phototrophic BacteriumRoseiflexus castenholzii

“…Filamentous anoxygenic phototrophs, therefore, have received considerable attention as an important group when considering the early evolution of photosynthetic organisms (4). The spectroscopic and biochemical properties of the photosynthetic apparatus in the group, however, have been studied only in C. aurantiacus, and the common properties of the photosynthetic apparatus in the filamentous anoxygenic phototrophic bacteria remain unclear.The photochemical reaction center (RC) of C. aurantiacus consists of L, M, and cytochrome subunits and is closely related to those of purple bacteria (5,30,34,35,39). The genes coding for the RC subunits and peripheral light-harvesting (LH) polypeptides are located in two puf operons in C. aurantiacus.…”

“…The photochemical reaction center (RC) of C. aurantiacus consists of L, M, and cytochrome subunits and is closely related to those of purple bacteria (5,30,34,35,39). The genes coding for the RC subunits and peripheral light-harvesting (LH) polypeptides are located in two puf operons in C. aurantiacus.…”

Application of thermostable reaction centers from Chloroflexus aurantiacus as a protonmotive force generating system

“…Reaction centers (RCs) of C. aurantiacus were isolated by a single DEAE-cellulose chromatography step, using a modification of the procedure described by Shiozawa et al [17]. The membrane fraction (derived from 50 g wet weight cells) was diluted to a total volume of 0.5 1 with 20 mM Tris/HC1 (pH 9.0) and solubilized with 1% dimethyldodecylamine N-oxide (Me2DodNO) (w/v) for 1 h at 40°C.…”

“…Furthermore, the optimum temperature for proton extrusion in C. aurantiacus has been found to be between 67 and 70°C [16]. A method for purification of bold RCs without attached B808-866 light harvesting system has been described [17]. RCs from C. aurantiacus have so far not functionally been reconstituted.…”