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At least 19 recordsLinked to original sources
PubMed2001

Cu2+ site in photosynthetic bacterial reaction centers from Rhodobacter sphaeroides, Rhodobacter capsulatus, and Rhodopseudomonas viridis.

The interaction of metal ions with isolated photosynthetic reaction centers (RCs) from the purple bacteria Rhodobacter sphaeroides, Rhodobacter capsulatus, and Rhodopseudomonas viridis has been investigated with transient optical and magnetic resonance techniques. In RCs from all species, the electrochromic response of the bacteriopheophytin cofactors associated with Q(A)(-)Q(B) --> Q(A)Q(B)(-) electron transfer is slowed in the presence of Cu(2+). This slowing is similar to the metal ion effect observed for RCs from Rb. sphaeroides where Zn(2+) was bound to a specific site on the surface of the RC [Utschig et al. (1998) Biochemistry 37, 8278]. The coordination environments of the Cu(2+) sites were probed with electron paramagnetic resonance (EPR) spectroscopy, providing the first direct spectroscopic evidence for the existence of a second metal site in RCs from Rb. capsulatus and Rps. viridis. In the dark, RCs with Cu(2+) bound to the surface exhibit axially symmetric EPR spectra. Electron spin echo envelope modulation (ESEEM) spectral results indicate multiple weakly hyperfine coupled (14)N nuclei in close proximity to Cu(2+). These ESEEM spectra resemble those observed for Cu(2+) RCs from Rb. sphaeroides [Utschig et al. (2000) Biochemistry 39, 2961] and indicate that two or more histidines ligate the Cu(2+) at the surface site in each RC. Thus, RCs from Rb. sphaeroides, Rb. capsulatus, and Rps. viridis each have a structurally analogous Cu(2+) binding site that is involved in modulating the Q(A)(-)Q(B) --> Q(A)Q(B)(-) electron-transfer process. Inspection of the Rps. viridis crystal structure reveals four potential histidine ligands from three different subunits (M16, H178, H72, and L211) located beneath the Q(B) binding pocket. The location of these histidines is surprisingly similar to the grouping of four histidine residues (H68, H126, H128, and L211) observed in the Rb. sphaeroides RC crystal structure. Further elucidation of these Cu(2+) sites will provide a means to investigate localized proton entry into the RCs of Rb. capsulatus and Rps. viridis as well as locate a site of protein motions coupled with electron transfer.

Binding Sites↗
PubMed1995

Phenotypic characterisation and genetic complementation of dimethylsulfoxide respiratory mutants of Rhodobacter sphaeroides and Rhodobacter capsulatus.

Two chlorate resistant mutants of Rhodobacter sphaeroides were isolated which were deficient in dimethylsulfoxide reductase activity. Immunoblotting experiments showed that the phenotype of these mutants and that of Rhodobacter capsulatus strain DK9, a mutant unable to reduce dimethylsulfoxide, was correlated with low or undetectable levels of the dimethylsulfoxide reductase apoprotein. All three mutants were complemented by a cosmid from a library of Rhodobacter sphaeroides genomic DNA. Further genetic complementation analysis revealed that functions required for restoration of dimethylsulfoxide reductase activity in the Rhodobacter sphaeroides mutants were encoded on an 9 kb EcoR1 DNA fragment derived from this cosmid. Expression of this 9 kb DNA fragment in Escherichia coli showed that it encoded the dimethylsulfoxide reductase structural gene of Rhodobacter sphaeroides.

Dimethyl Sulfoxide↗
PubMed1996

The membrane-bound cytochrome cy of Rhodobacter capsulatus can serve as an electron donor to the photosynthetic reaction of Rhodobacter sphaeroides.

Rhodobacter capsulatus has two different pathways for reduction of the photo-oxidized reaction center, one using water-soluble cytochrome c2, the other via membrane-associated cytochrome cy. Rhodobacter sphaeroides differs in that it lacks a cytochrome cy homologue capable of functioning in photosynthetic electron transfer; cytochrome c2 is thus the sole electron carrier, and is required for photosynthetic (Ps+) growth. Genetic evidence indicates that cytochrome cy of R. capsulatus can complement a Ps- cytochrome-c2-deficient mutant of R sphaeroides (Jenny, F.E. and Daldal, F (1993). EMBO J. 12, 1283-1292). Here, we show that it transfers electrons from cytochrome bc1 complex to the reaction center in R. sphaeroides, albeit at a lower rate than that catalyzed by the endogenous cytochrome c2. When cytochrome cy is expressed in R. sphaeroides in the presence of cytochrome c2, there is an increase in the amount of photo-oxidizable c-type cytochrome. In the absence of cytochrome c2, electron transfer via cytochrome cy shows significantly different kinetics for reaction center reduction and cytochrome c oxidation. These findings further establish that cytochrome cy, the electron carrier permitting soluble cytochrome c2-independent photosynthetic growth in R. capsulatus, can function in a similar capacity in R. sphaeroides.

Cytochrome c Group↗
PubMed1995

Electron transport-dependent taxis in Rhodobacter sphaeroides.

Rhodobacter sphaeroides showed chemotaxis to the terminal electron acceptors oxygen and dimethyl sulfoxide, and the responses to these effectors were shown to be influenced by the relative activities of the different electron transport pathways. R. sphaeroides cells tethered by their flagella showed a step-down response to a decrease in the oxygen or dimethyl sulfoxide concentration when using them as terminal acceptors. Bacteria using photosynthetic electron transport, however, showed a step-down response to oxygen addition. Addition of the proton ionophore carbonyl cyanide 4-trifluoromethoxyphenylhydrazone did not cause a transient behavioral response, although it decreased the electrochemical proton gradient (delta p) and increased the rate of electron transport. However, removal of the ionophore, which caused an increase in delta p and a decrease in the electron transport rate, resulted in a step-down response. Together, these data suggest that behavioral responses of R. sphaeroides to electron transport effectors are caused by changes in the rate of electron transport rather than changes in delta p.

Aerobiosis↗
PubMed1987

Ammonium and methylammonium transport in Rhodobacter sphaeroides.

Rhodobacter sphaeroides maintained intracellular ammonium pools of 1.1 to 2.6 mM during growth in several fixed nitrogen sources as well as during diazotrophic growth. Addition of 0.15 mM NH4+ to washed, nitrogen-free cell suspensions was followed by linear uptake of NH4+ from the medium and transient formation of intracellular pools of 0.9 to 1.5 mM NH4+. Transport of NH4+ was shown to be independent of assimilation by glutamine synthetase because intracellular pools of over 1 mM represented NH4+ concentration gradients of at least 100-fold across the cytoplasmic membrane. Ammonium pools of over 1 mM were also found in non-growing cell suspensions in nitrogen-free medium after glutamine synthetase was inhibited with methionine sulfoximine. In NH4+-free cell suspensions, methylammonium (14CH3NH3+) was taken up rapidly, and intracellular concentrations of 0.4 to 0.5 mM were maintained. The 14CH3NH3+ pool was not affected by methionine sulfoximine. Unlike NH4+ uptake, 14CH3NH3+ uptake in nitrogen-free cell suspensions was repressed by growth in NH4+. These results suggest that R. sphaeroides may produce an NH4+-specific transport system in addition to the NH4+/14CH3NH3+ transporter. This second transporter is able to produce normal-size NH4+ pools but has very little affinity for 14CH3NH3+ and is not repressed by growth in high concentrations of NH4+.

Biological Transport↗
PubMed2001

The roles of the multiple CheW and CheA homologues in chemotaxis and in chemoreceptor localization in Rhodobacter sphaeroides.

Rhodobacter sphaeroides has multiple homologues of most of the Escherichia coli chemotaxis genes, organized in two major operons and other, unlinked, loci. These include cheA1 and cheW1 (che Op1) and cheA2, cheW2 and cheW3 (che Op2). We have deleted each of these cheA and cheW homologues in-frame and examined the chemosensory behaviour of these strains on swarm plates and in tethered cell assays. In addition, we have examined the effect of these deletions on the polar localization of the chemoreceptor McpG. In E. coli, deletion of either cheA or cheW results in a non-chemotactic phenotype, and these strains also show no receptor clustering. Here, we demonstrate that CheW2 and CheA2 are required for the normal localization of McpG and for normal chemotactic responses under both aerobic and photoheterotrophic conditions. Under aerobic conditions, deletion of cheW3 has no significant effect on McpG localization and only has an effect on chemotaxis to shallow gradients in swarm plates. Under photoheterotrophic conditions, however, CheW3 is required for McpG localization and also for chemotaxis both on swarm plates and in the tethered cell assay. These phenotypes are not a direct result of delocalization of McpG, as this chemoreceptor does not mediate chemotaxis to any of the compounds tested and can therefore be considered a marker for general methyl-accepting chemotaxis protein (MCP) clustering. Thus, there is a correlation between the normal localization of McpG (and presumably other chemoreceptors) and chemotaxis. We propose a model in which the multiple different MCPs in R. sphaeroides are contained within a polar chemoreceptor cluster. Deletion of cheW2 and cheA2 under both aerobic and photoheterotrophic conditions, and cheW3 under photoheterotrophic conditions, disrupts the cluster and hence reduces chemotaxis to any compound sensed by these MCPs.

Aerobiosis↗
PubMed1988

Phenotypic and genetic characterization of cytochrome c2 deficient mutants of Rhodobacter sphaeroides.

Rhodobacter sphaeroides mutants lacking cytochrome c2 (cyt c2) have been constructed by site-specific recombination between the wild-type genomic cyt c2 structural gene (cycA) and a suicide plasmid containing a defective cyc operon where deletion of cycA sequences was accompanied by insertion of a KnR gene. Southern blot analysis confirmed that the wild-type cyc operon was exchanged for the inactivated cycA gene, presumably by double-reciprocal recombination. Spectroscopic and immunochemical measurements, together with genetic complementation, established that the inability of these mutants to grow under photosynthetic conditions was due to the lack of cyt c2. The cyt c2 deficient strains reduced photooxidized reaction center complexes approximately 4 orders of magnitude more slowly than the parent strain. The phenotype and characteristics of these mutants were restored when a wild-type cyc operon was introduced on a stable low copy number plasmid. These experiments provide the first genetic evidence for the obligatory role of cyt c2 in wild-type cyclic photosynthetic electron transport in R. sphaeroides. We have also observed that the R. sphaeroides cyt c2 deficient strains spontaneously gave rise to photosynthetically competent pseudorevertants at a frequency which suggests that the cyt c2 independent photosynthetic electron transport which suppresses the phenotype of the cyt c2 deficient strains was the result of a single mutation elsewhere in the genome.

Cytochrome c Group↗
PubMed1997

A quorum-sensing system in the free-living photosynthetic bacterium Rhodobacter sphaeroides.

Rhodobacter sphaeroides is a free-living, photoheterotrophic bacterium known for its genomic and metabolic complexity. We have discovered that this purple photosynthetic organism possesses a quorum-sensing system. Quorum sensing occurs in a number of eukaryotic host-associated gram-negative bacteria. In these bacteria there are two genes required for quorum sensing, the luxR and luxI homologs, and there is an acylhomoserine lactone signal molecule synthesized by the product of the luxI homolog. In R. sphaeroides, synthesis of a novel homoserine lactone signal, 7,8-cis-N-(tetradecenoyl)homoserine lactone, is directed by a luxI homolog termed cerI. Two open reading frames immediately upstream of cerI are proposed to be components of the quorum-sensing system. The first of these is a luxR homolog termed cerR, and the second is a small open reading frame of 159 bp. Inactivation of cerI in R. sphaeroides results in mucoid colony formation on agar and formation of large aggregates of cells in liquid cultures. Clumping of CerI mutants in liquid culture is reversible upon addition of the acylhomoserine lactone signal and represents a phenotype unlike those controlled by quorum sensing in other bacteria.

4-Butyrolactone↗
PubMed2003

Decolorization of azo dyes by Rhodobacter sphaeroides.

Rhodobacter sphaeroides AS1.1737 decolorized more than 90% of several azo dyes (200 mg dyes l(-1)) in 24 h. The optimal culture conditions were: anaerobic illumination (1990 1x), peptone as carbon source, temperature 35-40 degrees C and pH 7-8. Intracellular crude enzyme from this strain had azoreductase activity, optimized temperature as 45-50 degrees C, and decolorization kinetics which were consistent with a ping-pong mechanism.

Azo Compounds↗
PubMed2004

Characterization of Cu- and Zn-containing superoxide dismutase of Rhodobacter sphaeroides.

Rhodobacter sphaeroides has a cuprozinc-containing superoxide dismutase (CuZnSOD) in its periplasm in addition to the cytoplasmic SOD that appears to contain iron (FeSOD). The FeSOD is constitutively expressed under the growth conditions examined, whereas the CuZnSOD is detected only when the light-harvesting complexes are found. The CuZnSOD expression is regulated post-transcriptionally, and the enzyme appears to protect the photoheterotrophic cells from periplasmic superoxide that may be generated by exposure of the cells to low O2 under the illuminated conditions at 10 W/m2.

Cytosol↗
PubMed2001

CheR- and CheB-dependent chemosensory adaptation system of Rhodobacter sphaeroides.

Rhodobacter sphaeroides has multiple homologues of most of the Escherichia coli chemotaxis genes, organized in three major operons and other, unlinked, loci. These include cheA(1) and cheR(1) (che Op(1)) and cheA(2), cheR(2), and cheB(1) (che Op(2)). In-frame deletions of these cheR and cheB homologues were constructed and the chemosensory behaviour of the resultant mutants examined on swarm plates and in tethered cell assays. Under the conditions tested, CheR(2) and CheB(1) were essential for normal chemotaxis, whereas CheR(1) was not. cheR(2) and cheB(1), but not cheR(1), were also able to complement the equivalent E. coli mutants. However, none of the proteins were required for the correct polar localization of the chemoreceptor McpG in R. sphaeroides. In E. coli, CheR binds to the NWETF motif on the high-abundance receptors, allowing methylation of both high- and low-abundance receptors. This motif is not contained on any R. sphaeroides chemoreceptors thus far identified, although 2 of the 13 putative chemoreceptors, McpA and TlpT, do have similar sequences. This suggests that CheR(2) either interacts with the NWETF motif of E. coli methyl-accepting chemotaxis proteins (MCPs), even though its native motif may be slightly different, or with another conserved region of the MCPs. Methanol release measurements show that R. sphaeroides has an adaptation system that is different from that of Bacillus subtilis and E. coli, with methanol release measurable on the addition of attractant but not on its removal. Intriguingly, CheA(2), but not CheA(1), is able to phosphorylate CheB(1), suggesting that signaling through CheA(1) cannot initiate feedback receptor adaptation via CheB(1)-P.

Adaptation, Biological↗
PubMed1991

Evidence for two promoters for the cytochrome c2 gene (cycA) of Rhodobacter sphaeroides.

Rhodobacter sphaeroides cytochrome c2 (cyt c2) is a periplasmic heme protein, encoded by cycA, that is required for photosynthetic growth and for one branch of the aerobic electron transport chain. cycA mRNA and cyt c2 are more abundant photosynthetically than aerobically. We report here that there are four cycA transcripts by high-resolution Northern (RNA) blot analysis, and we have mapped 10 5' ends by primer extension. Complementation of a cycA null mutant shows that there are at least two cycA promoters: one within 89 bp upstream of the translation initiation codon for a transcript beginning at -28, and at least one within 484 bp upstream for the remaining nine 5' ends. The 5' ends at -28 and -137 are more abundant in aerobically grown cells, while those at -38, -155, -250, and -300 are more abundant photosynthetically. DNA sequences with homology to the Escherichia coli sigma 70 consensus promoter sequence precede the 5' ends at -28 and -274, and there is weak homology upstream of the -82 and -250 ends.

Amino Acid Sequence↗
PubMed1997

Reactions of isocytochrome c2 in the photosynthetic electron transfer chain of Rhodobacter sphaeroides.

Rhodobacter sphaeroides strains lacking cytochrome c2 (cyt c2), the normal electron donor to P870+ in light-oxidized reaction center (RC) complexes, are unable to grow photosynthetically. However, spd mutations that suppress the photosynthetic deficiency of cyt c2 mutants elevate levels of the cyt c2 isoform, isocyt c2. We monitored photosynthetic electron transfer in whole cells, in chromatophores, and with purified components to ascertain if and how isocyt c2 reduced light-oxidized RC complexes. These studies revealed that several fundamental aspects of photosynthetic electron transfer were similar in strains that use isocyt c2 and wild-type cells. For example, P870+ reduction accompanied cytochrome c oxidation. In addition, photosynthetic electron transfer was blocked by the well-known cyt bc1 complex inhibitors antimycin and myxothiazol. However, even at the increased isocyt c2 levels present in these strains (approximately 40% that of cyt c2 in wild-type cells), there was little, if any, of the rapid (< 5 microns) electron transfer to P870+ that is characteristic of cytochromes bound to RC complexes at the time of the light flash. Thus, it appears that isocyt c2 function limits the in vivo rate of P870+ reduction. Indeed, at low ionic strength in vitro, the apparent affinity of isocyt c2 for RC complexes (KD approximately 40 microM) is significantly lower than that of cyt c2 (KD approximately 1.0 microM). This reduced affinity does not appear to result from an altered mode of RC binding by isocyt c2 since electrostatic interactions make similar overall contributions to the binding of both cyt c2 and isocyt c2 to this membrane-bound redox partner. Thus, sequence, structural, or local conformational differences between cyt c2 and isocyt c2 significantly alter their apparent affinities for this physiologically relevant redox partner.

Cytochrome c Group↗
PubMed1994

Role of subunit IV in the cytochrome b-c1 complex from Rhodobacter sphaeroides.

Rhodobacter sphaeroides mutants lacking subunit IV (M(r) = 14,384) of the cytochrome b-c1 complex (representative mutant strain, RS delta IV-2) have been constructed by site-specific recombination between the wild-type genomic subunit IV structural gene (fbcQ) and a suicide plasmid containing a defective fbcQ sequence. RS delta IV-2 gives rise to a photosynthetically competent phenotype after a period of adaptation. The chemical compositions, spectral properties, and cytochrome b-c1 complex activities in subunit IV-deficient chromatophores from adapted RS delta IV-2 are similar to those in wild-type chromatophores. However, the apparent Km for Q2H2 for the b-c1 complex in subunit IV-deficient chromatophores from adapted RS delta IV-2 cells is about four times higher than that in chromatophores from wild-type cells. The cytochrome b-c1 complex activity in subunit IV-deficient chromatophores of adapted RS delta IV-2 cells is more labile to detergent treatment than that from wild-type cells. The specific activities of dodecylmaltoside-solubilized fractions of RS delta IV-2, based on cytochrome b, are only one-fourth that of the untreated chromatophores. Introducing a wild-type fbcQ operon on a stable low copy number plasmid, pRK415, into RS delta IV-2 restores photosynthetic growth behavior, the apparent Km value for Q2H2, and tolerance to detergent treatment to that of wild-type cells. Cytochrome b-c1 complex purified from adapted RS delta IV-2 contains only three subunits. It has only 25% of the activity of the four-subunit enzyme. This low activity is accompanied by an increase of the apparent Km for Q2H2 from 3 to 13 microM, suggesting that subunit IV may be involved in quinone binding in addition to its structural role.

Base Sequence↗
PubMed1993

The bc1 complexes of Rhodobacter sphaeroides and Rhodobacter capsulatus.

Photosynthetic bacteria offer excellent experimental opportunities to explore both the structure and function of the ubiquinol-cytochrome c oxidoreductase (bc1 complex). In both Rhodobacter sphaeroides and Rhodobacter capsulatus, the bc1 complex functions in both the aerobic respiratory chain and as an essential component of the photosynthetic electron transport chain. Because the bc1 complex in these organisms can be functionally coupled to the photosynthetic reaction center, flash photolysis can be used to study electron flow through the enzyme and to examine the effects of various amino acid substitutions. During the past several years, numerous mutations have been generated in the cytochrome b subunit, in the Rieske iron-sulfur subunit, and in the cytochrome c1 subunit. Both site-directed and random mutagenesis procedures have been utilized. Studies of these mutations have identified amino acid residues that are metal ligands, as well as those residues that are at or near either the quinol oxidase (Qo) site or the quinol reductase (Qi) site. The postulate that these two Q-sites are located on opposite sides of the membrane is supported by these studies. Current research is directed at exploring the details of the catalytic mechanism, the nature of the subunit interactions, and the assembly of this enzyme.

Amino Acid Sequence↗
PubMed2001

Role of the core region of the PufX protein in inhibition of reconstitution of the core light-harvesting complexes of Rhodobacter sphaeroides and Rhodobacter capsulatus.

PufX, the protein encoded by the pufX gene of Rhodobacter capsulatus and Rhodobacter sphaeroides, has been further characterized. The mature forms of these proteins contain 9 and 12 fewer amino acids, respectively, at the C-terminal end of the protein than are encoded by their pufX genes. To identify the portion of PufX responsible for inhibition of LH1 formation in reconstitution experiments, different regions (N-terminus and several core regions containing different lengths of the C-terminus) of Rb. sphaeroides and Rb. capsulatus PufX were chemically synthesized. Neither the N- nor C-terminal polypeptides of Rb. sphaeroides were inhibitory to LH1 reconstitution. However, all core segments were active, causing 50% inhibition at a concentration ratio of between 3:1 and 6:1 relative to the LH1 alpha-polypeptides whose concentrations were 3-4 microM. CD measurements indicated that the core segment containing 39 amino acids of Rb. sphaeroides PufX exhibited 47% alpha-helix in trifluoroethanol while the core segment containing 43 amino acids of Rb. capsulatus PufX exhibited 59 and 55% alpha-helix in trifluoroethanol and in 0.80% octylglucoside in water, respectively. Approximately 50% alpha-helix was also indicated by a PHD (Burkhard-Rost) structure prediction. Binding of bacteriochlorophyll to these PufX core segments is implicated.

Amino Acid Sequence↗
PubMed1998

The primary structures of the low-redox potential diheme cytochromes c from the phototrophic bacteria Rhodobacter sphaeroides and Rhodobacter adriaticus reveal a new structural family of c-type cytochromes.

The complete amino acid sequence of the low-redox potential cytochrome c-551.5 from Rhodobacter sphaeroides was determined by automated Edman degradation combined with mass spectroscopy. There are 139 residues and two typical Cys-X-X-Cys-His heme-binding sites. A homologous low-redox potential cytochrome was also sequenced from Rhodobacter adriaticus and was found to contain 126 residues. It is 53% identical to that of Rb. sphaeroides and has two internal deletions of one and five residues. The Rhodobacter diheme cytochromes are 21-24% identical to the translated open reading frame SLL1886 from Synechocystis sp. PCC6801. There are at least two deletions of five and eight residues in the 188-residue cyanobacterial protein. Each of the three cytochromes has more histidines than it needs to bind the two hemes, but conserved histidines located 23 residues after the first heme and 14-19 residues before the second heme are likely to be the sixth heme ligands. There is no evidence for gene doubling and no similarity to any other known cytochromes. The measured helix content of 24% is much less than normal for c-type cytochromes. These proteins thus appear to be representative of an entirely new class of c-type cytochromes.

Amino Acid Sequence↗
PubMed1987

The binding domain on horse cytochrome c and Rhodobacter sphaeroides cytochrome c2 for the Rhodobacter sphaeroides cytochrome bc1 complex.

The interaction of the Rhodobacter sphaeroides cytochrome bc1 complex with Rb. sphaeroides cytochrome c2 and horse cytochrome c was studied by using specific lysine modification and ionic strength dependence methods. The rate of the reactions with both cytochrome c and cytochrome c2 decreased rapidly with increasing ionic strength above 0.2 M NaCl. The ionic strength dependence suggested that electrostatic interactions were equally important to the reactions of the two cytochromes, even though they have opposite net charges at pH 7.0. In order to define the interaction domain on horse cytochrome c, the reaction rates of derivatives modified at single lysine amino groups with trifluoroacetyl or trifluoromethylphenylcarbamoyl were measured. Modification of lysine-8, -13, -27, -72, -79, and -87 surrounding the heme crevice was found to significantly lower the rate of the reaction, while modification of lysines in other regions had no effect. This result indicates that lysines surrounding the heme crevice of horse cytochrome c are involved in electrostatic interactions with carboxylate groups at the binding site on the cytochrome bc1 complex. In order to define the reaction domain on cytochrome c2, a fraction consisting of a mixture of singly labeled 4-carboxy-2,6-dinitrophenylcytochrome c2 derivatives modified at lysine-35, -88, -95, -97, and -105 and several unidentified lysines was prepared. Although it was not possible to resolve these derivatives, all of the identified lysines are located on the front surface of cytochrome c2 near the heme crevice. The rate of reaction of this fraction was significantly smaller than that of native cytochrome c2, suggesting that the binding domain on cytochrome c2 is also located at the heme crevice.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗