Isolation, sequence analysis, and transcriptional studies of the flavodoxin gene from Anacystis nidulans R2

Laudenbach, David E.; Reith, Michael; Straus, Neil A.

doi:10.1128/jb.170.1.258-265.1988

Cited by 132 publications

(89 citation statements)

References 39 publications

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“…The structure of the long-chain flavodoxin from Anacystis nidulans (169 residues [Smith et al, 1983;Laudenbach et al, 19871) is known in the ox state. Its sequence (Laudenbach et al, 1988) differs from that of A . 7120 (Leonhardt & Straus, 1989) by 31 Yo.…”

Section: St Rao Et Aimentioning

confidence: 85%

Structure of the oxidized long‐chain flavodoxin from anabaena 7120 at 2 å resolution

et al. 1992

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The structure of the long-chain flavodoxin from the photosynthetic cyanobacterium Anabaena 7120 has been determined at 2 A resolution by the molecular replacement method using the atomic coordinates of the long-chain flavodoxin from Anacystis nidulans. The structure of a third long-chain flavodoxin from Chondrus crispus has recently been reported. Crystals of oxidized A . 7120 flavodoxin belong to the monoclinic space group P2, with a = 48.0, b = 32.0, c = 51.6A, and 0 = 92", and one molecule in the asymmetric unit. The 2 A intensity data were collected with oscillation films at the CHESS synchrotron source and processed to yield 9,795 independent intensities with Rmerg of 0.07. Of these, 8,493 reflections had I > 2a and were used in the analysis. The model obtained by molecular replacement was initially refined by simulated annealing using the XPLOR program. Repeated refitting into omit maps and several rounds of conjugate gradient refinement led to an R-value of 0.185 for a model containing atoms for protein residues 2-169, flavin mononucleotide (FMN), and 104 solvent molecules. The FMN shows many interactions with the protein with the isoalloxazine ring, ribityl sugar, and the 5'-phosphate. The flavin ring has its pyrimidine end buried into the protein, and the functional dimethyl benzene edge is accessible to solvent. The FMN interactions in all three long-chain structures are similar except for the 04' of the ribityl chain, which interacts with the hydroxyl group of Thr 88 side chain in A. 7120, while with a water molecule in the other two. The phosphate group interacts with the atoms of the 9-15 loop as well as with NE1 of Trp 57. The N5 atom of flavin interacts with the amide NH of Ile 59 in A . 7120, whereas in A . nidulans it interacts with the amide NH of Val 59 in a similar manner. In C. crispus flavodoxin, N5 forms a hydrogen bond with the side chain hydroxyl group of the equivalent Thr 58. The hydrogen bond distances to the backbone NH groups in the first two flavodoxins are 3.6 A and 3.5 A , respectively, whereas in the third flavodoxin the distance is 3.1 A , close to the normal value. Even though the hydrogen bond distances are long in the first two cases, still they might have significant energy because their microenvironment in the protein is not accessible to solvent. In all three long-chain flavodoxins, a water molecule bridges the ends of the inserted loop in the os strand and minimally perturbs its hydrogen bonding with p4. Many of the water molecules in these proteins interact with the flavin binding loops. The conserved &core of the three long-chain and two short-chain flavodoxins superpose with root mean square deviations ranging from 0.48 A to 0.97 A .

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Section: St Rao Et Aimentioning

confidence: 85%

Structure of the oxidized long‐chain flavodoxin from anabaena 7120 at 2 å resolution

et al. 1992

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“…Under iron stress, the isiA gene is transcribed into two messages, a monocistronic message containing only isiA and a dicistronic message that also contains the isiB gene (10). Although the discovery of the CP43-like iron stress-induced protein was made some time ago (11), its precise function has not been elucidated.…”

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Three-dimensional Model and Characterization of the Iron Stress-induced CP43′-Photosystem I Supercomplex Isolated from the Cyanobacterium Synechocystis PCC 6803

Bibby¹,

Nield

Barber

2001

Journal of Biological Chemistry

107

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The cyanobacterium Synechocystis PCC 6803 has been subjected to growth under iron-deficient conditions. As a consequence, the isiA gene is expressed, and its product, the chlorophyll a-binding protein CP43, accumulates in the cell. Recently, we have shown for the first time that 18 copies of this photosystem II (PSII)-like chlorophyll a-binding protein forms a ring around the trimeric photosystem I (PSI) reaction center (Bibby, T. S., Nield, J., and Barber, J. (2001) Nature, 412, 743-745). Here we further characterize the biochemical and structural properties of this novel CP43-PSI supercomplex confirming that it is a functional unit of approximately 1900 kDa where the antenna size of PSI is increased by 70% or more. Using electron microscopy and single particle analysis, we have constructed a preliminary three-dimensional model of the CP43-PSI supercomplex and used it as a framework to incorporate higher resolution structures of PSI and CP43 recently derived from x-ray crystallography. Not only does this work emphasize the flexibility of cyanobacterial lightharvesting systems in response to the lowering of phycobilisome and PSI levels under iron-deficient conditions, but it also has implications for understanding the organization of the related chlorophyll a/b-binding Pcb proteins of oxychlorobacteria, formerly known as prochlorophytes.Iron is the most abundant transition metal in the crust of the earth and is an absolute requirement for photosynthetic organisms such as cyanobacteria, because it is needed for many of the redox reactions of the photosynthetic electron transport system. However, in most aquatic ecosystems it can be sufficiently low to limit photosynthetic activity (1, 2). This finding is attributed mainly to the low solubility of Fe 3ϩ above neutral pH in oxygenic ecosystems (3). As a result, cyanobacteria and other microorganisms have evolved a number of responses to cope with frequently occurring conditions of iron deficiency (4). One such response is to express two "iron stress-induced" genes, isiA and isiB (5, 6), which are located on the same operon. The isiB gene encodes for flavodoxin, which can functionally replace the iron containing ferredoxin (7). The isiA gene encodes for a protein often called CP43Ј, because it has an amino acid sequence homologous to that of the chlorophyll a-binding protein, CP43 of photosystem II (PSII) 1 (8, 9). Like CP43, CP43Ј is predicted to have six transmembrane helices, and judged by the conservation of histidine residues, it is likely to bind the same number of chlorophyll a molecules. The major difference is that CP43Ј lacks the large hydrophilic loop that joins the luminal ends of helices V and VI of CP43. For this reason, it has 342 amino acids rather than 472 (see Fig. 1).Under iron stress, the isiA gene is transcribed into two messages, a monocistronic message containing only isiA and a dicistronic message that also contains the isiB gene (10). Although the discovery of the CP43-like iron stress-induced protein was made some time ago (11), its precise...

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“…However, the largest sink for iron in the photosynthetic system is PSI, which contains 12 iron atoms in three Fe 4 -S 4 clusters (Jordan et al, 2001). Adaptations of the photosynthetic apparatus to iron limitation include the induction of a specific PSI antenna complex, CP43# (Boekema et al, 2001) and a flavodoxin protein that can serve as an alternative to ferredoxin in the electron transport chain (Laudenbach et al, 1988).Once iron is transported inside the cell, it needs to be stored in a way that prevents its interaction with various redox active components. The Synechocystis 6803 genome encodes two iron storage proteins that are 1 This work was supported by grants from the U.S. Department of Energy, (USDA-NRI grant no.…”

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Critical Roles of Bacterioferritins in Iron Storage and Proliferation of Cyanobacteria

2004

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Cyanobacteria are key contributors to global photosynthetic productivity, and iron availability is essential for cyanobacterial proliferation. While iron is abundant in the earth's crust, its unique chemical properties render it a limiting factor for photoautotrophic growth. As compared to other nonphotosynthetic organisms, oxygenic photosynthetic organisms such as cyanobacteria, algae, and green plants need large amounts of iron to maintain functional PSI complexes in their photosynthetic apparatus. Ferritins and bacterioferritins are ubiquitously present iron-storage proteins. We have found that in the cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis 6803), bacterioferritins are responsible for the storage of as much as 50% of cellular iron. Synechocystis 6803, as well as many other cyanobacterial species, have two bacterioferritins, BfrA and BfrB, in which either the heme binding or di-iron center ligating residues are absent. Purified bacterioferritin complex from Synechocystis 6803 has both BfrA and BfrB proteins. Targeted mutagenesis of each of the two bacterioferritin genes resulted in poor growth under iron-deprived conditions. Inactivation of both genes did not result in a more severe phenotype. These results support the presence of a heteromultimeric structure of Synechocystis bacterioferritin, in which one subunit ligates a diiron center while the other accommodates heme binding. Notably, the reduced internal iron concentrations in the mutant cells resulted in a lower content of PSI. In addition, they triggered iron starvation responses even in the presence of normal levels of external iron, thus demonstrating a central role of bacterioferritins in iron homeostasis in these photosynthetic organisms.Iron serves as a cofactor in a multitude of cellular processes. As such, iron accumulation and storage processes are essential for the survival of all organisms. However, the same redox properties that make iron a valuable cofactor also lead to oxidative interactions resulting in the formation of harmful radicals. Therefore, iron accumulation in the cells is tightly regulated to ensure that very little free iron is present (Kakhlon and Cabantchik, 2002).While iron is abundant in the earth's crust, the bioavailability of iron in the current oxidative terrestrial environment is limited. This is due to the fact that in the presence of dioxygen at neutral pH, iron precipitates as Fe(OH) 3 . As a consequence, the bioavailability of iron limits the proliferation of photosynthetic organisms. Indeed, studies conducted in the Southern Ocean have indicated that iron is a limiting factor for primary photosynthetic productivity (Falkowski et al., 1998). In many of the ecological niches occupied by photosynthetic organisms, iron concentrations are limited to nanomolar levels (Morel and Price, 2003). Surges in the iron concentration due to aeolian dust deposition are transient (Falkowski et al., 1998). To accommodate such an infrequent supply of iron, photosynthetic organisms must have efficient iron storage mec...

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Isolation, sequence analysis, and transcriptional studies of the flavodoxin gene from Anacystis nidulans R2

Cited by 132 publications

References 39 publications

Structure of the oxidized long‐chain flavodoxin from anabaena 7120 at 2 å resolution

Structure of the oxidized long‐chain flavodoxin from anabaena 7120 at 2 å resolution

Three-dimensional Model and Characterization of the Iron Stress-induced CP43′-Photosystem I Supercomplex Isolated from the Cyanobacterium Synechocystis PCC 6803

Critical Roles of Bacterioferritins in Iron Storage and Proliferation of Cyanobacteria

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