Two Genes Encoding New Carotenoid-Modifying Enzymes in the Green Sulfur Bacterium
            <i>Chlorobium tepidum</i>

Maresca, Julia A.; Bryant, Donald A.

doi:10.1128/jb.00766-06

Cited by 32 publications

(29 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Because horizontal transfer of carotenoid biosynthetic genes appears to occur frequently between unrelated microorganisms (54,55), this distribution leads one to question why cruA, as well as crtP, crtQ, and crtH, have not been transferred more broadly. The genes encoding phytoene synthases, CrtI-type carotenoid desaturases, and carotenoid glycosyltransferases are found not only in photosynthetic bacteria but also in Deinococcus radiodurans, the planctomycete Rhodopirellula baltica, actinomycetes, and archaea (17,24,25,51). The restricted distribution of CruA might indicate that some CruA cyclases require another protein subunit or a cofactor that is not commonly synthesized by many bacteria for optimal activity.…”

Section: Discussionmentioning

confidence: 99%

“…12, 13, and 51). The other genes in the chlorobactene biosynthetic pathway were identified on the basis of their similarity to genes involved in carotenoid biosynthesis in other organisms, and their functions were confirmed by targeted gene inactivation (12,51). However, this approach failed to identify the lycopene cyclase in C. tepidum (12), and, consequently, a complementation assay was used to identify the gene encoding the lycopene cyclase in GSB.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Identification of a fourth family of lycopene cyclases in photosynthetic bacteria

Maresca

Graham

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

133

View full text Add to dashboard Cite

A fourth and large family of lycopene cyclases was identified in photosynthetic prokaryotes. The first member of this family, encoded by the cruA gene of the green sulfur bacterium Chlorobium tepidum, was identified in a complementation assay with a lycopene-producing strain of Escherichia coli. Orthologs of cruA are found in all available green sulfur bacterial genomes and in all cyanobacterial genomes that lack genes encoding CrtL-or CrtY-type lycopene cyclases. The cyanobacterium Synechococcus sp. PCC 7002 has two homologs of CruA, denoted CruA and CruP, and both were shown to have lycopene cyclase activity. Although all characterized lycopene cyclases in plants are CrtL-type proteins, genes orthologous to cruP also occur in plant genomes. The CruA-and CruP-type carotenoid cyclases are members of the FixC dehydrogenase superfamily and are distantly related to CrtL-and CrtY-type lycopene cyclases. Identification of these cyclases fills a major gap in the carotenoid biosynthetic pathways of green sulfur bacteria and cyanobacteria.carotenogenesis ͉ carotenoids ͉ cyanobacteria ͉ green sulfur bacteria ͉ photosynthesis C olored carotenoids are found in nearly all photosynthetic species and in a variety of nonphotosynthetic organisms and play roles in light-harvesting, photoprotection, structural maintenance of pigment-protein complexes (1), and membrane structure and fluidity (2). The cyclization of the linear compound lycopene to produce ␣-, ␤-, ␥-, or -carotene is a branch point in carotenoid biosynthetic pathways in many species of bacteria, plants, and fungi (3, 4). The monocyclic ␥-carotene is a precursor to myxoxanthophylls in cyanobacteria (5, 6), is both an intermediate and an end product of carotenogenesis in orange and yellow flowers and fruits (7-10), and is an intermediate in chlorobactene biosynthesis in green sulfur bacteria (GSB) (11-13). Dicyclic ␤-carotene is a major component of photosystems (PS) I and II in cyanobacteria and plants (14,15) and is modified to isorenieratene in brown-colored GSB and some actinomycetes (16,17).Three classes of lycopene cyclases have previously been identified in bacteria: the CrtY-type ␤-cyclases that are found in many carotenogenic proteobacteria (e.g., refs. 18 and 19), Streptomyces spp. (17), and the Chloroflexi; the CrtL family, which includes the ␤-and -cyclases in some cyanobacteria and plants (20,21); and the heterodimeric cyclases of some Gram-positive bacteria (22, 23), which are related to the lycopene cyclases of archaea (24, 25) and halophilic bacteria (26). These classes are distantly related to each other and share only a few conserved motifs, including an N-terminal flavin-binding domain that is found in the first two groups but appears to be missing in the third (27). Carotenoid monocyclases are found in both the CrtY and CrtL families (28-30), and there are no obvious sequence differences between mono-and dicyclases (28).The cyclization of lycopene to ␥-or ␤-carotene is an isomerization reaction, which produces no net change in mass or redox state o...

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Identification of a fourth family of lycopene cyclases in photosynthetic bacteria

Maresca

Graham

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

133

View full text Add to dashboard Cite

show abstract

“…Homologs to other carotenoid biosynthetic genes in the genomes of GSB were also identified by using the predicted amino acid sequences of carotenoid biosynthesis genes from C. tepidum as queries in tblastn searches (21,36). A gene was considered orthologous if the E value of the match between the C. tepidum query sequence and its best match in another genome was less than 10 Ϫ80 .…”

Section: Methodsmentioning

confidence: 99%

Isorenieratene Biosynthesis in Green Sulfur Bacteria Requires the Cooperative Actions of Two Carotenoid Cyclases

2008

Self Cite

View full text Add to dashboard Cite

The cyclization of lycopene to ␥-or ␤-carotene is a major branch point in the biosynthesis of carotenoids in photosynthetic bacteria. Four families of carotenoid cyclases are known, and each family includes both monoand dicyclases, which catalyze the formation of ␥-and ␤-carotene, respectively. Green sulfur bacteria (GSB) synthesize aromatic carotenoids, of which the most commonly occurring types are the monocyclic chlorobactene and the dicyclic isorenieratene. Recently, the cruA gene, encoding a conserved hypothetical protein found in the genomes of all GSB and some cyanobacteria, was identified as a lycopene cyclase. Further genomic analyses have found that all available fully sequenced genomes of GSB encode an ortholog of cruA. Additionally, the genomes of all isorenieratene-producing species of GSB encode a cruA paralog, now named cruB. The cruA gene from the chlorobactene-producing GSB species Chlorobaculum tepidum and both cruA and cruB from the brown-colored, isorenieratene-producing GSB species Chlorobium phaeobacteroides strain DSM 266 T were heterologously expressed in lycopene-and neurosporene-producing strains of Escherichia coli, and the cruB gene of Chlorobium clathratiforme strain DSM 5477 T was also heterologously expressed in C. tepidum by inserting the gene at the bchU locus. The results show that CruA is probably a lycopene monocyclase in all GSB and that CruB is a ␥-carotene cyclase in isorenieratene-producing species. Consequently, the branch point for the synthesis of mono-and dicyclic carotenoids in GSB seems to be the modification of ␥-carotene, rather than the cyclization of lycopene as occurs in cyanobacteria.

show abstract

“…We also performed a BLAST search analysis with a cyanobacterial MGlcDG synthase and found that an ORF, CT1987, showed the highest identity (;20%) to the enzyme. However, CT1987 is a chlorobactene glucosyltransferase (named CruC) involved in carotenoid modification in this bacterium (Maresca and Bryant, 2006). These observations suggested that C. tepidum does not have any orthologs for either planttype MGDG synthases or cyanobacterial MGlcDG synthases.…”

Section: Galactolipid Roles In Photosynthesis 2645mentioning

confidence: 82%

A Monogalactosyldiacylglycerol Synthase Found in the Green Sulfur Bacterium Chlorobaculum tepidum Reveals Important Roles for Galactolipids in Photosynthesis

et al. 2011

View full text Add to dashboard Cite

Monogalactosyldiacylglycerol (MGDG), which is conserved in almost all photosynthetic organisms, is the most abundant natural polar lipid on Earth. In plants, MGDG is highly accumulated in the chloroplast membranes and is an important bulk constituent of thylakoid membranes. However, precise functions of MGDG in photosynthesis have not been well understood. Here, we report a novel MGDG synthase from the green sulfur bacterium Chlorobaculum tepidum. This enzyme, MgdA, catalyzes MGDG synthesis using UDP-Gal as a substrate. The gene encoding MgdA was essential for this bacterium; only heterozygous mgdA mutants could be isolated. An mgdA knockdown mutation affected in vivo assembly of bacteriochlorophyll c aggregates, suggesting the involvement of MGDG in the construction of the light-harvesting complex called chlorosome. These results indicate that MGDG biosynthesis has been independently established in each photosynthetic organism to perform photosynthesis under different environmental conditions. We complemented an Arabidopsis thaliana MGDG synthase mutant by heterologous expression of MgdA. The complemented plants showed almost normal levels of MGDG, although they also had abnormal morphological phenotypes, including reduced chlorophyll content, no apical dominance in shoot growth, atypical flower development, and infertility. These observations provide new insights regarding the importance of regulated MGDG synthesis in the physiology of higher plants. INTRODUCTIONLife on Earth mostly relies on energy from the sun that is converted to biochemical energy by photosynthesis. The coordinated control of the photochemical reaction is thus critically important for all living organisms. To date, six bacterial phyla with species capable of chlorophyll-based photosynthesis are known. They are Cyanobacteria, Proteobacteria (purple bacteria), Chloroflexi (anoxygenic filamentous bacteria), Chlorobi (green sulfur bacteria), Firmicutes (heliobacteria), and Acidobacteria Bryant et al., 2007). Photosynthetic bacteria that belong to Proteobacteria and Chloroflexi use the photosystem II (PSII) type reaction center, and those of Chlorobi, Firmicutes, and Acidobacteria use the photosystem I (PSI) type reaction center. Cyanobacteria use both types of reaction centers, which allows them to perform oxygenic photosynthesis. It is widely accepted that chloroplasts in plants and algae originated from an ancient cyanobacterium that was introduced into a proto-plant cell by endosymbiosis.Although only two types of reaction centers are used by the phototrophs, each species has evolved a wide variety of lightharvesting antennae that absorb photons and transfer excitation energy to the reaction centers (Green, 2003). The variation in antenna systems may reflect an adaptation to different environmental light conditions and the different colors and intensities of sunlight. Among the light-harvesting systems, chlorosomes, found in Chlorobi, Chloroflexi, and Acidobacteria, are the largest and the most efficient antenna systems in nature (Blankensh...

show abstract

Two Genes Encoding New Carotenoid-Modifying Enzymes in the Green Sulfur Bacterium Chlorobium tepidum

Cited by 32 publications

References 43 publications

Identification of a fourth family of lycopene cyclases in photosynthetic bacteria

Identification of a fourth family of lycopene cyclases in photosynthetic bacteria

Isorenieratene Biosynthesis in Green Sulfur Bacteria Requires the Cooperative Actions of Two Carotenoid Cyclases

A Monogalactosyldiacylglycerol Synthase Found in the Green Sulfur Bacterium Chlorobaculum tepidum Reveals Important Roles for Galactolipids in Photosynthesis

Contact Info

Product

Resources

About