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J F Briat

Publications and source records attributed to J F Briat.

12 recordsLinked to original sources
PubMed1992

Amino-acid sequence and predicted three-dimensional structure of pea seed (Pisum sativum) ferritin.

The iron storage protein, ferritin, is widely distributed in the living kingdom. Here the complete cDNA and derived amino-acid sequence of pea seed ferritin are described, together with its predicted secondary structure, namely a four-helix-bundle fold similar to those of mammalian ferritins, with a fifth short helix at the C-terminus. An N-terminal extension of 71 residues contains a transit peptide (first 47 residues) responsible for plastid targetting as in other plant ferritins, and this is cleaved before assembly. The second part of the extension (24 residues) belongs to the mature subunit; it is cleaved during germination. The amino-acid sequence of pea seed ferritin is aligned with those of other ferritins (49% amino-acid identity with H-chains and 40% with L-chains of human liver ferritin in the aligned region). A three-dimensional model has been constructed by fitting the aligned sequence to the coordinates of human H-chains, with appropriate modifications. A folded conformation with an 11-residue helix is predicted for the N-terminal extension. As in mammalian ferritins, 24 subunits assemble into a hollow shell. In pea seed ferritin, its N-terminal extension is exposed on the outside surface of the shell. Within each pea subunit is a ferroxidase centre resembling those of human ferritin H-chains except for a replacement of Glu-62 by His. The channel at the 4-fold-symmetry axes defined by E-helices, is predicted to be hydrophilic in plant ferritins, whereas it is hydrophobic in mammalian ferritins.

Amino Acid Sequence↗
PubMed1992

Purification, characterization and function of bacterioferritin from the cyanobacterium Synechocystis P.C.C. 6803.

Storage and buffering of iron is achieved by a class of proteins, the ferritins, widely distributed throughout the living kingdoms. All ferritins have in common their three-dimensional structure and their ability to store large amounts of iron in their central cavity. However, eukaryotic ferritins from plants and animals and bacterioferritins have no sequence similarity, and besides non-haem iron bacterioferritins contain haem residues whereas eukaryotic ferritins do not. In this paper we report the first purification and characterization of a bacterioferritin from a cyanobacterium. It has a molecular mass of 400 kDa and is built up from 19 kDa subunits. Its N-terminal sequence shows 73% identity with that of the Escherichia coli bacterioferritin subunit. It contains 2300 atoms of iron and 1500 molecules of phosphate per ferritin molecule and 0.25 haem residue per subunit; the alpha-peak of the cytochrome has its maximum at 559 nm. In contrast with what is known for eukaryotic ferritins, we found that bacterioferritin from Synechocystis is not inducible by iron under the conditions that we have tested and that it has a constant concentration whatever the iron status of the cells, even at very low iron concentration. Bacterioferritin from Synechocystis P.C.C. 6803 is fully assembled in vivo and it is shown by labelling with 59Fe that it is able to load iron in vitro as well as in vivo. Bacterioferritin from Synechocystis is shown to have an iron-buffering function while the bulk of cellular iron is found associated with a pool of low-molecular-mass electronegative molecules. The role of Synechocystis bacterioferritin in iron metabolism is discussed.

Amino Acid Sequence↗
PubMed1992

Iron induces ferritin synthesis in maize plantlets.

The iron-storage protein ferritin has been purified to homogeneity from maize seeds, allowing to determine the sequence of the first 29 NH2-terminal amino acids of its subunit and to raise specific rabbit polyclonal antibodies. Addition of 500 microM Fe-EDTA/75 microM Fe-citrate to hydroponic culture solutions of maize plantlets, previously starved for iron, led to a significant increase of the iron concentration of roots and leaves, albeit root iron was mainly found associated with the apoplast. Immunodetection of ferritin by western blots indicated that this iron treatment induced ferritin protein accumulation in roots and leaves over a period of 3 days. In order to investigate this induction at the ferritin mRNA level, various ferritin cDNA clones were isolated from a cDNA library prepared from poly(A)+ mRNA isolated from roots 48 h after iron treatment. These cDNAs were classified into two groups called FM1 and FM2. Upstream of the sequence encoding the mature ferritin subunit, both of these cDNAs contained an in-frame coding sequence with the characteristics of a transit peptide for plastid targeting. Two members of the FM1 subfamily, both partial at their 5' extremity, were characterized. They are identical, except in their 3' untranslated region: FM1A extends 162 nucleotides beyond the 3' terminus of FM1B. These two mRNAs could arise from the use of two different polyadenylation signals. FM2 is 96% identical to FM1 and contains 45 nucleotides of 5' untranslated region. Northern analyses of root and leaf RNAs, at different times after iron treatment, revealed ferritin mRNA accumulation in response to iron. Ferritin mRNA accumulation was transient and particularly abundant in leaves, reaching a maximum at 24 h. The level of ferritin mRNA in roots was affected to a lesser extent than in leaves.

Amino Acid Sequence↗
PubMed1991

Ferritin gene transcription is regulated by iron in soybean cell cultures.

Iron-regulated ferritin synthesis in animals is dominated by translational control of stored mRNA; iron-induced transcription of ferritin genes, when it occurs, changes the subunit composition of ferritin mRNA and protein and is coupled to translational control. Ferritins in plants and animals have evolved from a common progenitor, based on the similarity of protein sequence; however, sequence divergence occurs in the C termini; structure prediction suggests that plant ferritin has the E-helix, which, in horse ferritin, forms a large channel at the tetrameric interface. In contemporary plants, a transit peptide is encoded by ferritin mRNA to target the protein to plastids. Iron-regulated synthesis of ferritin in plants and animals appears to be very different since the 50- to 60-fold increases of ferritin protein, previously observed to be induced by iron in cultured soybean cells, is accompanied by an equivalent accumulation of hybridizable ferritin mRNA and by increased transcription of ferritin genes. Ferritin mRNA from iron-induced cells and the constitutive ferritin mRNA from soybean hypocotyls are identical. The iron-induced protein is translocated normally to plastids. Differences in animal ferritin structure coincide with the various iron storage functions (reserve for iron proteins and detoxification). In contrast, the constancy of structure of soybean ferritin, iron-induced and constitutive, coupled with the potential for vacuolar storage of excess iron in plants suggest that rapid synthesis of ferritin from a stored ferritin mRNA may not be needed in plants for detoxification of iron.

Amino Acid Sequence↗
PubMed1991

Ferritin accumulation and degradation in different organs of pea (Pisum sativum) during development.

Iron concentration and ferritin distribution have been determined in different organs of pea (Pisum sativum) during development under conditions of continuous iron supply from hydroponic cultures. No ferritin was detected in total protein extracts from roots or leaves. However, a transient iron accumulation in the roots, which corresponds to an increase in iron uptake, was observed when young fruits started to develop. Ferritin was detectable in total protein extracts of flowers and pods, and it accumulated in seeds. In seeds, the same relative amount of ferritin was detected in cotyledons and in the embryo axis. In cotyledons, ferritin and iron concentration decrease progressively during the first week of germination. Ferritin in the embryo axis was processed, and disappeared, during germination, within the first 4 days of radicle and epicotyl growth. This degradation of ferritin in vivo was marked by a shortening of a 28 kDa subunit, giving 26.5 and 25 kDa polypeptides, reminiscent of the radical damage occurring in pea seed ferritin during iron exchange in vitro [Laulhere, Laboure & Briat (1989) J. Biol. Chem. 264, 3629-3635]. Developmental control of iron concentration and ferritin distribution in different organs of pea is discussed.

Fabaceae↗
PubMed1990

Purification and characterization of an iron-induced ferritin from soybean (Glycine max) cell suspensions.

Ferric citrate induces ferritin synthesis and accumulation in soybean (Glycine max) cell suspension cultures [Proudhon, Briat & Lescure (1989) Plant Physiol. 90, 586-590]. This iron-induced ferritin has been purified from cells grown for 72 h in the presence of either 100 microM- or 500 microM-ferric citrate. It has a molecular mass of about 600 kDa and is built up from a 28 kDa subunit which is recognized by antibodies raised against pea (Pisum sativum) seed ferritin and it has the same N-terminal sequence as this latter, except for residue number 3, which is alanine in pea seed ferritin instead of valine in iron-induced soybean cell ferritin. It contains an average of 1800 atoms of iron per molecule whatever the ferric citrate concentration used to induce its synthesis. It is shown that the presence of 100 microM- or 500 microM-ferric citrate in the culture medium leads respectively to an 11- and 28-fold increase in the total intracellular iron concentration and to a 30- and 60-fold increase in the ferritin concentration. However, the percentage of iron stored in the mineral core of ferritin remains constant whatever the ferric citrate concentration used and represents only 5-6% of cellular iron.

Amino Acid Sequence↗
PubMed1990

Evidence for conservation of ferritin sequences among plants and animals and for a transit peptide in soybean.

Ferritin is a large multisubunit protein that stores iron in plants, animals, and bacteria. In animals, the protein is mainly cytoplasmic and is highly conserved, while in plants ferritin is found in chloroplasts and other plastids. Ferritin is synthesized in plants as a larger precursor of the mature subunit. There is no sequence information for ferritin from plants, except an NH2-terminal peptide of 35 residues which shows little similarity to any known ferritin sequences or transit peptides (Laulhere, J. P., Laboure, A. M., and Briat, J. F. (1989) J. Biol. Chem. 264, 3629-3635). To understand the genetic origin and the location of ferritin synthesis in plant cells, as well as the structure of ferritin from plants, we have sequenced both CNBr peptides from pea seed ferritin and nucleotides of a soybean hypocotyl ferritin cDNA, identified using a frog ferritin cDNA as a probe. Comparison of pea and soybean sequences showed an identity of 89%. Alignment of the plant ferritin sequences with animal ferritins showed 55-65% sequence identity in the common regions. However, a peptide of 28 amino acids extended the NH2 terminus of the plant ferritins. Furthermore, the cDNA encoded additional amino acids which appear to be a transit peptide. None of the sequences in soybean ferritin were found in the tobacco chloroplast genome, suggesting, as does the transit peptide, a nuclear location of ferritin gene(s) in plants. Plant ferritin mRNA is 400-500 nucleotides longer than animal ferritin mRNAs, a difference accounted for in part by the extra peptides encoded. The size of soybean ferritin mRNA was constant in different tissues but expression varied in different tissues (leaf greater than hypocotyl). Thus, higher plants and animal ferritins display sequence homology and differential tissue expression. An ancient, common progenitor apparently gave rise to contemporary eukaryotic ferritins after specific modifications, e.g. transport to plasmids.

Amino Acid Sequence↗
PubMed1990

Photoreduction and incorporation of iron into ferritins.

Pea seed ferritin is able to incorporate ferrous iron into the mineral core. Fe2+ may be formed by reduction of exogenous Fe3+ with ascorbate or by photoreduction by ferritin and by ferric citrate. In our experimental conditions the bulk of the photoreduction is carried out by ferritin, which is able to photoreduce its endogenous iron. Citrate does not enhance the photoreduction capacity of ferritin, and exogenous ferric citrate improves the yield of the reaction by about 30%. The mineral core of the ferritin is shown to photoreduce actively, and the protein shell does not participate directly in the photoreduction. Low light intensities and low concentration of reducing agents do not allow a release of iron from ferritins, but induce a 'redox mill' of photoreduction and simultaneous ferroxidase-mediated incorporation. High ascorbate concentrations induce the release of ferritin iron. These reactions are accompanied by the correlated occurrence of damage caused by radicals arising from Fenton reactions, leading to specific cleavages in the 28 kDa phytoferritin subunit. This damage caused by radicals occurs during the oxidative incorporation into the mineral core and is prevented by o-phenanthroline or by keeping the samples in the dark.

Ascorbic Acid↗
PubMed1979

Transcription activity of a DNA-protein complex isolated from spinach plastids.

A DNA . protein complex of about 150 S is isolated from purified spinach chloroplasts by Sepharose 4B gel filtration. A DNA-dependent RNA polymerase activity is found associated with the complex. This DNA protein complex is able to initiate RNA chains in vitro. The RNA synthesis is more dependent on CTP than other nucleoside triphosphates. 50% of the activity is still present with 0.6 M KCl. The temperature optimum occurs between 30 degrees C and 35 degrees C. Rifampicin and rifamycin SV have no inhibitory effect. TNA products have been characterized by gel filtration and by hybridization with chloroplast DNA (ctDNA). At the beginning of transcription DNA products are linked to the transcription complex and are later detached. The molecular weight of the product ranges between 0.07 X 10(6) and 2 X 10(6). A part of the product (3--4%) has a molecular weight higher than 2 X 10(6). No endogenous RNase activity was present during the molecular weight determinations experiments. Hybridization experiments show that at least 75% of the RNA products are hybridizable with ctDNA and that 40% of these products are composed of chloroplast ribosomal RNA, showing that rDNA is preferentially transcribed.

Chloroplasts↗
PubMedDate not supplied

Structure, function, and evolution of ferritins.

The ferritins of animals and plants and the bacterioferritins (BFRs) have a common iron-storage function in spite of differences in cytological location and biosynthetic regulation. The plant ferritins and BFRs are more similar to the H chains of mammals than to mammalian L chains, with respect to primary structure and conservation of ferroxidase center residues. Hence they probably arose from a common H-type ancestor. The recent discovery in E. coli of a second type of iron-storage protein (FTN) resembling ferritin H chains raises the question of what the relative roles of these two proteins are in this organism. Mammalian L ferritins lack ferroxidase centers and form a distinct group. Comparison of the three-dimensional structures of mammalian and invertebrate ferritins, as well as computer modeling of plant ferritins and of BFR, indicate a well conserved molecular framework. The characterisation of numerous ferritin homopolymer variants has allowed the identification of some of the residues involved in iron uptake and an investigation of some of the functional differences between mammalian H and L chains.

Amino Acid Sequence↗
PubMedDate not supplied

Transcription of the chloroplast DNA: a review.

The transcription systems of chloroplasts and bacteria share different properties. The genetic material of chloroplasts is organized in the same way as bacterial nucleoids. The regulatory DNA sequences for transcription have a strong homology with their E. coli counterparts and some regulatory mechanisms could be conserved. The RNA polymerase subunits and some transcription factors also share similarities with prokaryotes. However, the chloroplast core-enzyme seems to be synthesized in the cytoplasm from nuclear encoded messages.

Amino Acid Sequence↗