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1.
Methods Mol Biol ; 1876: 25-35, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30317472

RESUMO

Enzymes with homology to nitrogenase are essential for the reduction of chemically stable double bonds within the biosynthetic pathways of bacteriochlorophyll and coenzyme F430. These tetrapyrrole-based compounds are crucial for bacterial photosynthesis and the biogenesis of methane in methanogenic archaea. Formation of bacteriochlorophyll requires the unique ATP-dependent enzyme chlorophyllide oxidoreductase (COR) for the two-electron reduction of chlorophyllide to bacteriochlorophyllide. COR catalysis is based on the homodimeric protein subunit BchX2, which facilitates the transfer of electrons to the corresponding heterotetrameric catalytic subunit (BchY/BchZ)2. By analogy to the nitrogenase system, the dynamic switch protein BchX2 contains a [4Fe-4S] cluster that triggers the ATP-driven transfer of electrons onto a second [4Fe-4S] cluster located in (BchY/BchZ)2. The subsequent substrate reduction and protonation is unrelated to nitrogenase catalysis, with no further involvement of a molybdenum-containing cofactor. The biosynthesis of the nickel-containing coenzyme F430 includes the six-electron reduction of the tetrapyrrole macrocycle of Ni2+-sirohydrochlorin a,c-diamide to Ni2+-hexahydrosirohydrochlorin a,c-diamide catalyzed by CfbC/D. The homodimeric CfbC2 subunit carrying a [4Fe-4S] cluster shows close homology to BchX2. Accordingly, parallelism for the initial ATP-driven electron transfer steps of CfbC/D was proposed. Electrons are received by the dimeric catalytic subunit CfbD2, which contains a second [4Fe-4S] cluster and carries out the saturation of an overall of three double bonds in a highly orchestrated spatial and regioselective process. Following a short introduction to nitrogenase catalysis, this chapter will focus on the recent progress toward the understanding of the nitrogenase-like enzymes COR and CfbC/D, with special emphasis on the underlying enzymatic mechanism(s).


Assuntos
Oxirredutases do Álcool/metabolismo , Archaea/enzimologia , Bacterioclorofilas/biossíntese , Metaloporfirinas/metabolismo , Nitrogenase/química , Trifosfato de Adenosina/metabolismo , Oxirredutases do Álcool/química , Archaea/química , Proteínas Arqueais/química , Proteínas Arqueais/metabolismo , Catálise , Complexos Multienzimáticos/química , Complexos Multienzimáticos/metabolismo , Níquel , Homologia de Sequência de Aminoácidos
2.
Microbiology ; 164(11): 1416-1431, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30222098

RESUMO

The in vivo physiological role of the gene cobZ, which encodes precorrin-3B synthase, which catalyzes the initial porphyrin ring contraction step of cobalamin biosynthesis via the cob pathway, has been demonstrated here for the first time. Cobalamin is known to be essential for an early step of bacteriochlorophyll biosynthesis in anoxygenic purple bacteria. The cobZ (cobZRR) gene of the purple bacterium Rhodospirillum rubrum was localized to a 23.5 kb insert of chromosomal DNA contained on the cosmid pSC4. pSC4 complemented several mutants of bacteriochlorophyll and carotenoid biosynthesis, due to the presence of the bchCX and crtCDEF genes at one end of the cosmid insert, flanking cobZRR. A second gene, citB/tcuB, immediately downstream of cobZRR, shows homologies to both a tricarballylate oxidoreductase (tcuB) and a gene (citB) involved in signal transduction during citrate uptake. CobZRR shows extensive homology to the N-terminal domain of the bifunctional CobZ from Rhodobacter capsulatus, and the R. rubrum citB/tcuB gene is homologous to the CobZ C-terminal domain. A mutant, SERGK25, containing a terminatorless kanamycin interposon inserted into cobZRR, could not grow by anaerobic photosynthesis, but grew normally under dark, aerobic and microaerophilic conditions with succinate and fructose as carbon sources. The anaerobic in vivo activity of CobZ indicates that it does not require oxygen as a substrate. The mutant excreted large amounts of protoporphyrin IX-monomethylester, a brown precursor of bacteriochlorophyll biosynthesis. The mutant was complemented either by the cobZRR gene in trans, or when exogenous cobalamin was added to the medium. A deletion mutant of tcuB/citB did not exhibit the cob phenotype. Thus, a role for tcuB/citB in cobalamin biosynthesis could not be confirmed.


Assuntos
Fotossíntese/fisiologia , Rhodospirillum rubrum , Vitamina B 12/biossíntese , Sequência de Aminoácidos , Bacterioclorofilas/biossíntese , Carotenoides/biossíntese , Cosmídeos/genética , DNA Bacteriano/genética , Deleção de Genes , Metiltransferases/genética , Oxirredutases/genética , Oxigênio/metabolismo , Porfirinas/metabolismo , Rhodospirillum rubrum/enzimologia , Rhodospirillum rubrum/genética , Rhodospirillum rubrum/metabolismo
3.
J Biol Chem ; 293(39): 15233-15242, 2018 09 28.
Artigo em Inglês | MEDLINE | ID: mdl-30126840

RESUMO

Chlorobaculum tepidum, a green sulfur bacterium, utilizes chlorobactene as its major carotenoid, and this organism also accumulates a reduced form of this monocyclic pigment, 1',2'-dihydrochlorobactene. The protein catalyzing this reduction is the last unidentified enzyme in the biosynthetic pathways for all of the green sulfur bacterial pigments used for photosynthesis. The genome of C. tepidum contains two paralogous genes encoding members of the FixC family of flavoproteins: bchP, which has been shown to encode an enzyme of bacteriochlorophyll biosynthesis; and bchO, for which a function has not been assigned. Here we demonstrate that a bchO mutant is unable to synthesize 1',2'-dihydrochlorobactene, and when bchO is heterologously expressed in a neurosporene-producing mutant of the purple bacterium, Rhodobacter sphaeroides, the encoded protein is able to catalyze the formation of 1,2-dihydroneurosporene, the major carotenoid of the only other organism reported to synthesize 1,2-dihydrocarotenoids, Blastochloris viridis Identification of this enzyme completes the pathways for the synthesis of photosynthetic pigments in Chlorobiaceae, and accordingly and consistent with its role in carotenoid biosynthesis, we propose to rename the gene cruI Notably, the absence of cruI in B. viridis indicates that a second 1,2-carotenoid reductase, which is structurally unrelated to CruI (BchO), must exist in nature. The evolution of this carotenoid reductase in green sulfur bacteria is discussed herein.


Assuntos
Bacterioclorofilas/biossíntese , Carotenoides/biossíntese , Chlorobi/enzimologia , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Bacterioclorofilas/química , Bacterioclorofilas/genética , Vias Biossintéticas/genética , Carotenoides/química , Carotenoides/genética , Carotenoides/metabolismo , Chlorobi/química , Chlorobium/enzimologia , Chlorobium/genética , Genoma Bacteriano/genética , Oxirredutases/química , Oxirredutases/genética , Fotossíntese/genética
4.
Nat Prod Rep ; 35(7): 660-694, 2018 07 18.
Artigo em Inglês | MEDLINE | ID: mdl-29633774

RESUMO

Covering: up to the end of 2017 C-C bond formations are frequently the key steps in cofactor and natural product biosynthesis. Historically, C-C bond formations were thought to proceed by two electron mechanisms, represented by Claisen condensation in fatty acids and polyketide biosynthesis. These types of mechanisms require activated substrates to create a nucleophile and an electrophile. More recently, increasing number of C-C bond formations catalyzed by radical SAM enzymes are being identified. These free radical mediated reactions can proceed between almost any sp3 and sp2 carbon centers, allowing introduction of C-C bonds at unconventional positions in metabolites. Therefore, free radical mediated C-C bond formations are frequently found in the construction of structurally unique and complex metabolites. This review discusses our current understanding of the functions and mechanisms of C-C bond forming radical SAM enzymes and highlights their important roles in the biosynthesis of structurally complex, naturally occurring organic molecules. Mechanistic consideration of C-C bond formation by radical SAM enzymes identifies the significance of three key mechanistic factors: radical initiation, acceptor substrate activation and radical quenching. Understanding the functions and mechanisms of these characteristic enzymes will be important not only in promoting our understanding of radical SAM enzymes, but also for understanding natural product and cofactor biosynthesis.


Assuntos
Produtos Biológicos/química , Coenzimas/biossíntese , Enzimas/química , Enzimas/metabolismo , S-Adenosilmetionina/metabolismo , Adenina/análogos & derivados , Adenina/biossíntese , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Bacterioclorofilas/biossíntese , Produtos Biológicos/metabolismo , Carbono/química , Coenzimas/química , Endopeptidases/química , Endopeptidases/metabolismo , Hidrolases/química , Hidrolases/metabolismo , Molibdênio/química , Molibdênio/metabolismo , Tunicamicina/biossíntese , Vitamina K 2/metabolismo
5.
Biochim Biophys Acta Bioenerg ; 1859(7): 501-509, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29496394

RESUMO

Engineering photosynthetic bacteria to utilize a heterologous reaction center that contains a different (bacterio) chlorophyll could improve solar energy conversion efficiency by allowing cells to absorb a broader range of the solar spectrum. One promising candidate is the homodimeric type I reaction center from Heliobacterium modesticaldum. It is the simplest known reaction center and uses bacteriochlorophyll (BChl) g, which absorbs in the near-infrared region of the spectrum. Like the more common BChls a and b, BChl g is a true bacteriochlorin. It carries characteristic C3-vinyl and C8-ethylidene groups, the latter shared with BChl b. The purple phototrophic bacterium Rhodobacter (Rba.) sphaeroides was chosen as the platform into which the engineered production of BChl gF, where F is farnesyl, was attempted. Using a strain of Rba. sphaeroides that produces BChl bP, where P is phytyl, rather than the native BChl aP, we deleted bchF, a gene that encodes an enzyme responsible for the hydration of the C3-vinyl group of a precursor of BChls. This led to the production of BChl gP. Next, the crtE gene was deleted, thereby producing BChl g carrying a THF (tetrahydrofarnesol) moiety. Additionally, the bchGRs gene from Rba. sphaeroides was replaced with bchGHm from Hba. modesticaldum. To prevent reduction of the tail, bchP was deleted, which yielded BChl gF. The construction of a strain producing BChl gF validates the biosynthetic pathway established for its synthesis and satisfies a precondition for assembling the simplest reaction center in a heterologous organism, namely the biosynthesis of its native pigment, BChl gF.


Assuntos
Bacterioclorofilas/biossíntese , Rhodobacter sphaeroides/metabolismo , Vias Biossintéticas , Fotossíntese , Fosfatos de Poli-Isoprenil/biossíntese , Rhodobacter sphaeroides/genética
6.
Photosynth Res ; 135(1-3): 319-328, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-28643169

RESUMO

A chlorosome is a large and efficient light-harvesting antenna system found in some photosynthetic bacteria. This system comprises self-aggregates of bacteriochlorophyll (BChl) c, d, or e possessing a chiral 1-hydroxyethyl group at the 3-position, which plays a key role in the formation of the supramolecule. Biosynthesis of chlorosomal pigments involves stereoselective conversion of 3-vinyl group to 3-(1-hydroxyethyl) group facilitated by a 3-vinyl hydratase. This 3-vinyl hydration also occurs in BChl a biosynthesis, followed by oxidation that introduces an acetyl group at the 3-position. Herein, we present in vitro enzymatic assays of paralogous 3-vinyl hydratases derived from green sulfur bacteria, Chlorobaculum tepidum and Chlorobaculum limnaeum, the filamentous anoxygenic phototroph Chloroflexus aurantiacus, and the chloracidobacterium Chloracidobacterium thermophilum. All the hydratases showed hydration activities. The biosynthetic pathway of BChl a and other chlorosomal pigments is discussed considering the substrate specificity and stereoselectivity of the present hydratases.


Assuntos
Bacterioclorofilas/biossíntese , Chlorobi/enzimologia , Ensaios Enzimáticos/métodos , Hidroliases/metabolismo , Fotossíntese , Bacterioclorofilas/química , Vias Biossintéticas , Cromatografia Líquida de Alta Pressão , Metilação , Água/metabolismo
7.
Z Naturforsch C J Biosci ; 72(3-4): 99-105, 2017 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-28121619

RESUMO

Two local hydrogen-evolving strains of purple nonsulfur bacteria have been isolated, characterized, and identified as Rhodopseudomonas sp. TUT (strains Rh1 and Rh2). Lactate followed by succinate and malate supported the highest amounts of H2 production, growth (O.D.660nm, proteins and bacteriochlorphyll contents), nitrogenase activity, and uptake hydrogenase; the least of which was acetate. Alginate-immobilized cells evolved higher hydrogen amounts than free cell counterparts. Rh1 was more productive than Rh2 at all circumstances. Lactate-dependent hydrogen evolution was more than twice that of acetate, due to ATP productivity (2/-1, respectively), which is limiting to the nitrogenase activity. The preference of lactate over other acids indicates the feasibility of using these two strains in hydrogen production from dairy wastewater.


Assuntos
Ácido Acético/farmacologia , Células Imobilizadas/efeitos dos fármacos , Metabolismo Energético , Hidrogênio/metabolismo , Ácido Láctico/farmacologia , Rodopseudomonas/efeitos dos fármacos , Ácido Acético/metabolismo , Trifosfato de Adenosina/metabolismo , Alginatos/química , Bacterioclorofilas/biossíntese , Células Imobilizadas/metabolismo , Ácido Glucurônico/química , Ácidos Hexurônicos/química , Hidrogenase/biossíntese , Cinética , Ácido Láctico/metabolismo , Malatos/metabolismo , Malatos/farmacologia , Nitrogenase/biossíntese , Fotossíntese/fisiologia , Rodopseudomonas/metabolismo , Ácido Succínico/metabolismo , Ácido Succínico/farmacologia
8.
J Biol Chem ; 292(4): 1361-1373, 2017 01 27.
Artigo em Inglês | MEDLINE | ID: mdl-27994052

RESUMO

Green bacteria are chlorophotorophs that synthesize bacteriochlorophyll (BChl) c, d, or e, which assemble into supramolecular, nanotubular structures in large light-harvesting structures called chlorosomes. The biosynthetic pathways of these chlorophylls are known except for one reaction. Null mutants of bciD, which encodes a putative radical S-adenosyl-l-methionine (SAM) protein, are unable to synthesize BChl e but accumulate BChl c; however, it is unknown whether BciD is sufficient to convert BChl c (or its precursor, bacteriochlorophyllide (BChlide) c) into BChl e (or BChlide e). To determine the function of BciD, we expressed the bciD gene of Chlorobaculum limnaeum strain DSMZ 1677T in Escherichia coli and purified the enzyme under anoxic conditions. Electron paramagnetic resonance spectroscopy of BciD indicated that it contains a single [4Fe-4S] cluster. In assays containing SAM, BChlide c or d, and sodium dithionite, BciD catalyzed the conversion of SAM into 5'-deoxyadenosine and BChlide c or d into BChlide e or f, respectively. Our analyses also identified intermediates that are proposed to be 71-OH-BChlide c and d Thus, BciD is a radical SAM enzyme that converts the methyl group of BChlide c or d into the formyl group of BChlide e or f This probably occurs by a mechanism involving consecutive hydroxylation reactions of the C-7 methyl group to form a geminal diol intermediate, which spontaneously dehydrates to produce the final products, BChlide e or BChlide f The demonstration that BciD is sufficient to catalyze the conversion of BChlide c into BChlide e completes the biosynthetic pathways for all "Chlorobium chlorophylls."


Assuntos
Proteínas de Bactérias/metabolismo , Bacterioclorofilas/biossíntese , Chlorobi/enzimologia , Proteínas com Ferro-Enxofre/metabolismo , Metionina Adenosiltransferase/metabolismo , Proteínas de Bactérias/genética , Bacterioclorofilas/genética , Chlorobi/genética , Proteínas com Ferro-Enxofre/genética , Metionina Adenosiltransferase/genética
9.
Adv Exp Med Biol ; 925: 147-161, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-27957709

RESUMO

The sophisticated biochemistry of nitrogenase plays a fundamental role for the biosynthesis of tetrapyrrole molecules, acting as key components of photosynthesis and methanogenesis. Three nitrogenase-like metalloenzymes have been characterized to date. Synthesis of chlorophylls and bacteriochlorophylls involves the reduction of the C17-C18 double bond of the conjugated ring system of protochlorophyllide which is catalyzed by the multi-subunit enzyme dark operative protochlorophyllide oxidoreductase (DPOR). Subsequently, biosynthesis of all bacteriochlorophylls requires the reduction of the C7-C8 double bond by a second nitrogenase-like enzyme termed chlorophyllide oxidoreductase (COR). Mechanistically, DPOR and COR make use of a reductase component which links ATP hydrolysis to conformational changes. This dynamic switch protein is triggering the transient association between the reductase and the core catalytic protein complex, thereby facilitating the transduction of electrons via two [4Fe4S] clusters. X-ray crystallographic structural investigations in combination with biochemical experiments revealed the molecular basis of the underlying energy transduction mechanism. The unique nickel-containing tetrapyrrole cofactor F430 is located in the active site of methyl-coenzyme M reductase, which is catalyzing the final step of methane formation in methanogenic archaea. The nitrogenase-like protein NflH/NflD has been proposed to catalyze one or more ring reduction steps during the biosynthesis of F430. The present working hypothesis mirrors a DPOR and COR related enzyme mechanism of NflH/NflD. Furthermore, nfl-encoded proteins were suggested as "simplified" ancestors lying basal in the phylogenetic tree between nitrogenase and DPOR/COR.


Assuntos
Proteínas de Bactérias/química , Bacterioclorofilas/química , Nitrogenase/química , Oxirredutases atuantes sobre Doadores de Grupo CH-CH/química , Oxirredutases/química , Tetrapirróis/química , Azotobacter vinelandii/genética , Azotobacter vinelandii/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Bacterioclorofilas/biossíntese , Biocatálise , Expressão Gênica , Nitrogenase/genética , Nitrogenase/metabolismo , Oxirredução , Oxirredutases/genética , Oxirredutases/metabolismo , Oxirredutases atuantes sobre Doadores de Grupo CH-CH/genética , Oxirredutases atuantes sobre Doadores de Grupo CH-CH/metabolismo , Fotossíntese/genética , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , Estrutura Terciária de Proteína , Rhodobacter capsulatus/genética , Rhodobacter capsulatus/metabolismo , Roseobacter/genética , Roseobacter/metabolismo , Tetrapirróis/biossíntese
10.
Bioorg Med Chem ; 24(18): 4165-4170, 2016 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-27427396

RESUMO

The green sulfur photosynthetic bacterium Chlorobaculum (Cba.) tepidum was grown in liquid cultures containing perfluoro-1-decanol, 1H,1H,2H,2H-heptadecafluoro-1-decanol [CF3(CF2)7(CH2)2OH] or 1H,1H-nonadecafluoro-1-decanol [CF3(CF2)8CH2OH], to introduce rigid and fluorophilic chains into the esterifying moiety of light-harvesting bacteriochlorophyll (BChl) c. Exogenous 1H,1H,2H,2H-heptadecafluoro-1-decanol was successfully attached to the 17(2)-carboxy group of bacteriochlorophyllide (BChlide) c in vivo: the relative ratio of the unnatural BChl c esterified with this perfluoroalcohol over the total BChl c was 10.3%. Heat treatment of the liquid medium containing 1H,1H,2H,2H-heptadecafluoro-1-decanol with ß-cyclodextrin before inoculation increased the relative ratio of the BChl c derivative esterified with this alcohol in the total BChl c in Cba. tepidum. In a while, 1H,1H-nonadecafluoro-1-decanol was not attached to BChlide c in Cba. tepidum, which was grown by its supplementation. These results suggest that the rigidity close to the hydroxy group of the esterifying alcohol is not suitable for the recognition by the BChl c synthase called BchK in Cba. tepidum. The unnatural BChl c esterified with 1H,1H,2H,2H-heptadecafluoro-1-decanol participated in BChl c self-aggregates in chlorosomes.


Assuntos
Proteínas de Bactérias/biossíntese , Bacterioclorofilas/biossíntese , Chlorobi/metabolismo , Fluorcarbonetos/química , Pigmentos Biológicos/biossíntese , Proteínas de Bactérias/química , Proteínas de Bactérias/isolamento & purificação , Bacterioclorofilas/química , Bacterioclorofilas/isolamento & purificação , Ésteres/química , Ésteres/metabolismo , Álcoois Graxos/química , Complexos de Proteínas Captadores de Luz/química , Pigmentos Biológicos/química , Pigmentos Biológicos/isolamento & purificação , Temperatura , beta-Ciclodextrinas/química
11.
ACS Synth Biol ; 5(9): 948-54, 2016 09 16.
Artigo em Inglês | MEDLINE | ID: mdl-27171912

RESUMO

Improvements to photosynthetic efficiency could be achieved by manipulating pigment biosynthetic pathways of photosynthetic organisms in order to increase the spectral coverage for light absorption. The development of organisms that can produce both bacteriochlorophylls and chlorophylls is one way to achieve this aim, and accordingly we have engineered the bacteriochlorophyll-utilizing anoxygenic phototroph Rhodobacter sphaeroides to make chlorophyll a. Bacteriochlorophyll and chlorophyll share a common biosynthetic pathway up to the precursor chlorophyllide. Deletion of genes responsible for the bacteriochlorophyll-specific modifications of chlorophyllide and replacement of the native bacteriochlorophyll synthase with a cyanobacterial chlorophyll synthase resulted in the production of chlorophyll a. This pigment could be assembled in vivo into the plant water-soluble chlorophyll protein, heterologously produced in Rhodobacter sphaeroides, which represents a proof-of-principle for the engineering of novel antenna complexes that enhance the spectral range of photosynthesis.


Assuntos
Proteínas de Bactérias/biossíntese , Vias Biossintéticas/fisiologia , Clorofila/biossíntese , Plantas/metabolismo , Bacterioclorofilas/biossíntese , Clorofila A , Cianobactérias/metabolismo , Fotossíntese/fisiologia , Proteínas de Plantas/biossíntese , Rhodobacter sphaeroides/metabolismo
12.
J Bacteriol ; 198(15): 2056-63, 2016 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-27215788

RESUMO

UNLABELLED: The characteristic green color associated with chlorophyll pigments results from the formation of an isocyclic fifth ring on the tetrapyrrole macrocycle during the biosynthesis of these important molecules. This reaction is catalyzed by two unrelated cyclase enzymes employing different chemistries. Oxygenic phototrophs such as plants and cyanobacteria utilize an oxygen-dependent enzyme, the major component of which is a diiron protein named AcsF, while BchE, an oxygen-sensitive [4Fe-4S] cluster protein, dominates in phototrophs inhabiting anoxic environments, such as the purple phototrophic bacterium Rhodobacter sphaeroides We identify a potential acsF in this organism and assay for activity of the encoded protein in a strain lacking bchE under various aeration regimes. Initially, cells lacking bchE did not demonstrate AcsF activity under any condition tested. However, on removal of a gene encoding a subunit of the cbb3-type respiratory terminal oxidase, cells cultured under regimes ranging from oxic to micro-oxic exhibited cyclase activity, confirming the activity of the oxygen-dependent enzyme in this model organism. Potential reasons for the utilization of an oxygen-dependent enzyme in anoxygenic phototrophs are discussed. IMPORTANCE: The formation of the E ring of bacteriochlorophyll pigments is the least well characterized step in their biosynthesis, remaining enigmatic for over 60 years. Two unrelated enzymes catalyze this cyclization step; O2-dependent and O2-independent forms dominate in oxygenic and anoxygenic phototrophs, respectively. We uncover the activity of an O2-dependent enzyme in the anoxygenic purple phototrophic bacterium Rhodobacter sphaeroides, initially by inactivation of the high-affinity terminal respiratory oxidase, cytochrome cbb3 We propose that the O2-dependent form allows for the biosynthesis of a low level of bacteriochlorophyll under oxic conditions, so that a rapid initiation of photosynthetic processes is possible for this bacterium upon a reduction of oxygen tension.


Assuntos
Bacterioclorofilas/biossíntese , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Regulação Bacteriana da Expressão Gênica/fisiologia , Regulação Enzimológica da Expressão Gênica/fisiologia , Rhodobacter sphaeroides/enzimologia , Sequência de Aminoácidos , Bacterioclorofilas/química , Complexo IV da Cadeia de Transporte de Elétrons/genética , Deleção de Genes , Estrutura Molecular , Mutação , Rhodobacter sphaeroides/genética , Rhodobacter sphaeroides/metabolismo
13.
Photosynth Res ; 130(1-3): 33-45, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26816140

RESUMO

The photosynthetic green sulfur bacterium Chlorobaculum (Cba.) tepidum produces bacteriochlorophyll (BChl) c pigments bearing a chiral 1-hydroxyethyl group at the 3-position, which self-aggregate to construct main light-harvesting antenna complexes, chlorosomes. The secondary alcoholic hydroxy group is requisite for chlorosomal aggregation and biosynthesized by hydrating the 3-vinyl group of their precursors. Using recombinant proteins of Cba. tepidum BchF and BchV, we examined in vitro enzymatic hydration of some 3-vinyl-chlorophyll derivatives. Both the enzymes catalyzed stereoselective hydration of zinc 3-vinyl-8-ethyl-12-methyl-bacteriopheophorbide c or d to the zinc 31 R-bacteriopheophorbide c or d homolog, respectively, with a slight amount of the 31 S-epimric species. A similar R-stereoselectivity was observed in the BchF-hydration of zinc 3-vinyl-8-ethyl- and propyl-12-ethyl-bacteriopheophorbides c, while their BchV-hydration gave a relatively larger amount of the 31 S-epimers. The in vitro stereoselective hydration confirmed the in vivo production of the S-epimeric species by BchV. The enzymatic hydration for the above 8-propylated substrate proceeded more slowly than that for the 8-ethylated, and the 8-isobutylated substrate was no longer hydrated. Based on these results, biosynthetic pathways of BChl c homologs and epimers are proposed.


Assuntos
Proteínas de Bactérias/biossíntese , Bacterioclorofilas/biossíntese , Chlorobi/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Bacterioclorofilas/química , Vias Biossintéticas , Chlorobi/enzimologia , Cromatografia Líquida de Alta Pressão , Técnicas In Vitro , Estrutura Molecular , Estereoisomerismo
14.
Biochim Biophys Acta ; 1857(3): 288-95, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26341017

RESUMO

Cyanobacteria contain a family of genes encoding one-helix high-light-inducible proteins (Hlips) that are homologous to light harvesting chlorophyll a/b-binding proteins of plants and algae. Based on various experimental approaches used for their study, a spectrum of functions that includes regulation of chlorophyll biosynthesis, transient chlorophyll binding, quenching of singlet oxygen and non-photochemical quenching of absorbed energy is ascribed to Hlips. However, these functions had not been supported by conclusive experimental evidence until recently when it became clear that Hlips are able to quench absorbed light energy and assist during terminal step(s) of the chlorophyll biosynthesis and early stages of Photosystem II assembly. In this review we summarize and discuss the present knowledge about Hlips and provide a model of how individual members of the Hlip family operate during the biogenesis of chlorophyll-proteins, namely Photosystem II. This article is part of a Special Issue entitled Organization and dynamics of bioenergetic systems in bacteria, edited by Conrad Mullineaux.


Assuntos
Proteínas de Bactérias/biossíntese , Bacterioclorofilas/biossíntese , Cianobactérias/metabolismo , Complexos de Proteínas Captadores de Luz/biossíntese
15.
J Basic Microbiol ; 55(11): 1319-25, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26193456

RESUMO

Photosystem formation in anaerobic anoxygenic phototrophic bacteria (APB) is repressed by oxygen but is de-repressed when oxygen tension decreases. Under semiaerobic conditions, the synthesis of photopigments and pigment protein complexes in Rhodobacter (Rba.) sphaeroides are repressed by light. AppA, a blue-light receptor, mediates this regulation. In the present study, it was showed that the synthesis of bacteriochlorophyll, carotenoid, and pigment protein complexes in Rba. azotoformans 134K20 was significantly repressed by oxygen. Oxygen exposure also led to a conversion of spheroidene to spheroidenone. In semiaerobically growing cells, light irradiation resulted in a decrease in the formation of photosystem, and blue light was found to be the most effective light source. Blue light reduced the contents of bacteriochlorophyll and carotenoid slightly, but had negligible effects on light harvesting complex (LH) 1 content, whereas the content of LH2 was significantly decreased indicating that blue light selectively repressed the synthesis of LH2 in semiaerobically growing 134K20. It was concluded that, similar to Rba. sphaeroides, a blue light receptor presented in strain 134K20 played important roles in its light-dependent repression. A possible mechanism involved in controlling the differential inhibitory of blue light on the synthesis of photosystem was discussed.


Assuntos
Complexos de Proteínas Captadores de Luz/fisiologia , Rhodobacter/fisiologia , Bacterioclorofilas/biossíntese , Carotenoides/biossíntese , Carotenoides/química , Carotenoides/metabolismo , Luz , Complexos de Proteínas Captadores de Luz/efeitos da radiação , Rhodobacter/efeitos da radiação , Rhodobacter sphaeroides/química , Rhodobacter sphaeroides/fisiologia
16.
Sci Rep ; 5: 9741, 2015 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-25978726

RESUMO

In previous studies we have demonstrated that chlorophyllide a oxidoreductases (CORs) from bacteriochlorophyll (BChl) a-producing Rhodobacter species and BChl b-producing Blastochloris viridis show distinct substrate recognition and different catalytic hydrogenation reactions, and that these two types of CORs therefore cause committed steps for BChls a and b biosynthesis. In this study, COR genes from B. viridis were incorporated and overexpressed in a series of Rhodobacter sphaeroides mutants. We found that the following two factors are essential in making R. sphaeroides produce BChl b: the loss of functions of both intrinsic COR and 8-vinyl reductase (BciA) in the host R. sphaeroides strain; and expression of the BchYZ catalytic components of COR from B. viridis, not the complete set of COR (BchXYZ), in the host strain. In addition, we incorporated bchYZ of B. viridis into the R. sphaeroides mutant lacking BchJ and BciA, resulting in the strain accumulating both BChl a and BChl b. This is the first example of an anoxygenic photosynthetic bacterium producing BChls a and b together. The results suggest that BchJ enhances activity of the intrinsic COR. The physiological significance of BchJ in pigment biosynthetic pathways will be discussed.


Assuntos
Bacterioclorofilas/biossíntese , Vias Biossintéticas , Mutação , Oxigenases/genética , Rhodobacter sphaeroides/genética , Rhodobacter sphaeroides/metabolismo , Cromatografia Líquida de Alta Pressão , Ativação Enzimática , Expressão Gênica , Oxigenases/metabolismo , Pigmentos Biológicos/química , Pigmentos Biológicos/metabolismo
17.
Bioresour Technol ; 179: 505-509, 2015 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-25575211

RESUMO

This study is aimed at enhancing biomass and pigments production together with pollution removal in photosynthetic bacteria (PSB) wastewater treatment via different light sources. Red, yellow, blue, white LED and incandescent lamp were used. Results showed different light sources had great effects on the PSB. PSB had the highest biomass production, COD removal and biomass yield with red LED. The corresponding biomass, COD removal and biomass yield reached 2580 mg/L, 88.6% and 0.49 mg-biomass/mg-COD-removal, respectively. The hydraulic retention time of wastewater treatment could be shortened to 72 h with red LED. Mechanism analysis showed higher ATP was produced with red LED than others. Light sources could significantly affect the pigments production. The pigments productions were greatly higher with LED than incandescent lamp. Yellow LED had the highest pigments production while red LED produced the highest carotenoid/bacteriochlorophyll ratio. Considering both efficiency and energy cost, red LED was the optimal light source.


Assuntos
Bacterioclorofilas/biossíntese , Biomassa , Carotenoides/biossíntese , Fotossíntese/efeitos da radiação , Rodopseudomonas/metabolismo , Águas Residuárias/microbiologia , Purificação da Água/métodos , Trifosfato de Adenosina/metabolismo , Biodegradação Ambiental/efeitos da radiação , Análise da Demanda Biológica de Oxigênio , Luz , Rodopseudomonas/efeitos da radiação
18.
Microbiology ; 161(Pt 1): 120-30, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25336470

RESUMO

It is commonly accepted that green filamentous anoxygenic phototrophic (FAP) bacteria are the most ancient representatives of phototrophic micro-organisms. Modern FAPs belonging to the order Chloroflexales are divided into two suborders: Chloroflexineae and Roseiflexineae. Representatives of Roseiflexineae lack chlorosomes and synthesize bacteriochlorophyll a, whereas those of Chloroflexineae synthesize bacteriochlorophylls a and c and utilize chlorosomes for light harvesting. Though they constitute a small number of species, FAPs are quite diverse in their physiology. This bacterial group includes autotrophs and heterotrophs, thermophiles and mesophiles, aerobes and anaerobes, occupying both freshwater and halophilic environments. The anaerobic mesophilic autotroph Oscillochloris trichoides DG-6 is still not well studied in its physiology, and its evolutionary origin remains unclear. The goals of this study included identification of the reaction centre type of O. trichoides DG-6, reconstruction of its bacteriochlorophyll biosynthesis pathways, and determination of its evolutionary relationships with other FAPs. By enzymic and genomic analysis, the presence of RCII in O. trichoides DG-6 was demonstrated and the complete gene set involved in biosynthesis of bacteriochlorophylls a and c was established. We found that the bacteriochlorophyll gene sets differed between aerobic and anaerobic FAPs. The aerobic FAP genomes code oxygen-dependent AcsF cyclases, but lack the bchQ/bchR genes, which have been associated with adaptation to low light conditions in the anaerobic FAPs. A scenario of evolution of FAPs belonging to the order Chloroflexales is proposed.


Assuntos
Bacterioclorofilas/biossíntese , Evolução Biológica , Vias Biossintéticas , Chloroflexi/fisiologia , Hipóxia/metabolismo , Fotossíntese , Chloroflexi/classificação , Análise por Conglomerados , Genes Bacterianos , Genoma Bacteriano , Luz , Consumo de Oxigênio , Filogenia , RNA Ribossômico 16S/genética
19.
J Biol Inorg Chem ; 20(2): 435-45, 2015 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-25491285

RESUMO

Nitrogenase catalyzes biological nitrogen fixation, a key step in the global nitrogen cycle. Three homologous nitrogenases have been identified to date, along with several structural and/or functional homologs of this enzyme that are involved in nitrogenase assembly, bacteriochlorophyll biosynthesis and methanogenic process, respectively. In this article, we provide an overview of the structures and functions of nitrogenase and its homologs, which highlights the similarity and disparity of this uniquely versatile group of enzymes.


Assuntos
Bacterioclorofilas/biossíntese , Molibdênio/química , Fixação de Nitrogênio , Nitrogenase/química , Azotobacter vinelandii/enzimologia , Bacterioclorofilas/química , Catálise , Nitrogênio/química , Nitrogenase/metabolismo , Relação Estrutura-Atividade
20.
FEBS Lett ; 588(20): 3770-7, 2014 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-25176411

RESUMO

We report production of chlorophyll f and chlorophyll d in the cyanobacterium Chlorogloeopsis fritschii cultured under near-infrared and natural light conditions. C. fritschii produced chlorophyll f and chlorophyll d when cultured under natural light to a high culture density in a 20 L bubble column photobioreactor. In the laboratory, the ratio of chlorophyll f to chlorophyll a changed from 1:15 under near-infrared, to an undetectable level of chlorophyll f under artificial white light. The results provide support that chlorophylls f and d are both red-light inducible chlorophylls in C. fritschii.


Assuntos
Bacterioclorofilas/biossíntese , Cianobactérias/efeitos da radiação , Raios Infravermelhos , Bacterioclorofilas/efeitos da radiação , Reatores Biológicos , Cianobactérias/crescimento & desenvolvimento , Cianobactérias/metabolismo
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