Bayesian model of disease progression in GNE myopathy

One Sentence Summary: A Bayesian repeated measures model based on quantitative muscle strength data from a prospective Natural History Study was developed to determine disease progression and design clinical trials for GNE myopathy, a rare and slowly progressive muscle disease. GNE myopathy is a rare muscle disease characterized by slowly progressive weakness and atrophy of skeletal muscles. To address the significant challenges of defining the natural history and designing clinical trials for GNE myopathy, we developed a Bayesian latent variable repeated measures model to determine disease progression. The model is based on longitudinal quantitative muscle strength data collected as part of a prospective Natural History Study. The GNE Myopathy Progression Model provides an understanding of disease progression that would have otherwise required a natural history of unfeasible duration. "Disease age," the model-generated measure of disease progression, highly correlates with a variety of clinical, functional and patient-reported outcomes. With the incorporation of a treatment effect parameter to the GNE Disease Progression Model, we describe a novel GNE Myopathy Disease Modification Analysis that significantly increases power and reduces the number of subjects required to test the effectiveness of novel therapies when compared to more traditional analysis methods. The GNE Myopathy Disease Progression Model and Disease Modification Analysis can be applied to muscle diseases with prospectively collected muscle strength data, and a variety of rare and slowly progressive diseases.

Methicillin resistance study in clinical isolates of coagulase-negative staphylococci and determination of their susceptibility to alternative antimicrobial agents

AIMS

To achieve reliable detection of methicillin resistance in clinical isolates of coagulase-negative staphylococci.

METHODS AND RESULTS

Strains (105) were evaluated by normatized antimicrobial susceptibility methods, and for the presence of the methicillin resistance-determining mecA gene, using the polymerase chain reaction. Correlation between phenotypic and genotypic methods was obtained in 87.6% of the samples. Six strains, classified as methicillin-susceptible by phenotypic assays, revealed the presence of the mecA gene, indicating that methicillin resistance expression was probably repressed. Another seven isolates failed to show mecA amplification after displaying methicillin resistance in phenotypic evaluations. The susceptibility of the methicillin-resistant isolates to other antimicrobial agents was variable.

CONCLUSION

Genotypic determination of the mecA gene proved to be the most reliable method for detection of methicillin resistance.

SIGNIFICANCE AND IMPACT OF THE STUDY

Correct assessment of methicillin resistance, such as that attained through genotyping, is essential for defining therapeutic strategies, particularly when treating severely compromised patients.

Competition between C-terminal tyrosine and nicotinamide modulates pyridine nucleotide affinity and specificity in plant ferredoxin-NADP(+) reductase

Chloroplast ferredoxin-NADP(+) reductase has a 32,000-fold preference for NADPH over NADH, consistent with its main physiological role of NADP(+) photoreduction for de novo carbohydrate biosynthesis. Although it is distant from the 2'-phosphoryl group of NADP(+), replacement of the C-terminal tyrosine (Tyr(308) in the pea enzyme) by Trp, Phe, Gly, and Ser produced enzyme forms in which the preference for NADPH over NADH was decreased about 2-, 10-, 300-, and 400-fold, respectively. Remarkably, in the case of the Y308S mutant, the k(cat) value for the NADH-dependent activity approached that of the NADPH-dependent activity of the wild-type enzyme. Furthermore, difference spectra of the NAD(+) complexes revealed that the nicotinamide ring of NAD(+) binds at nearly full occupancy in the active site of both the Y308G and Y308S mutants. These results correlate well with the k(cat) values obtained with these mutants in the NADH-ferricyanide reaction. The data presented support the hypothesis that specific recognition of the 2'-phosphate group of NADP(H) is required but not sufficient to ensure a high degree of discrimination against NAD(H) in ferredoxin-NADP(+) reductase. Thus, the C-terminal tyrosine enhances the specificity of the reductase for NADP(H) by destabilizing the interaction of a moiety common to both coenzymes, i.e. the nicotinamide.

The role of photosynthetic electron transport in the oxidative degradation of chloroplastic glutamine synthetase

The stability of chloroplastic glutamine synthetase (GS; EC 6.3.1.2) was investigated under photooxidative stress using wheat (Triticum aestivum L.) leaves, chloroplasts, and chloroplast lysates. Illuminated seedlings sprayed with the superoxide radical (O-(2)) propagator methyl viologen showed rapid GS decline dependent on MV concentration and exposure time. Degradation products of approximately 39 and 31 kD were detected when chloroplast lysates containing both stroma and thylakoids were illuminated in the presence of MV or H(2)O(2). In all cases, GS cleavage was prevented by the addition of the electron transport inhibitor 3-(3, 4-dichlorophenyl)-1,1-dimethylurea. Full protection against degradation could also be obtained by the incorporation of chelators or antioxidant enzymes. Maximal rates of degradation required the presence of transition metals and reducing compounds such as NADPH or dithiothreitol. Similar patterns of GS cleavage were obtained when seedlings were exposed to high doses of irradiation. The results indicate that chloroplastic GS is extremely prone to oxidative cleavage, and that reduced transition metals, presumably resulting from the destruction of iron-sulfur clusters by light-generated O-(2), play a crucial role in the degradation process. The physiological implications of GS lability to oxidative stress are discussed.

A productive NADP+ binding mode of ferredoxin-NADP + reductase revealed by protein engineering and crystallographic studies

The flavoenzyme ferredoxin-NADP+ reductase (FNR) catalyzes the production of NADPH during photosynthesis. Whereas the structures of FNRs from spinach leaf and a cyanobacterium as well as many of their homologs have been solved, none of these studies has yielded a productive geometry of the flavin-nicotinamide interaction. Here, we show that this failure occurs because nicotinamide binding to wild type FNR involves the energetically unfavorable displacement of the C-terminal Tyr side chain. We used mutants of this residue (Tyr 308) of pea FNR to obtain the structures of productive NADP+ and NADPH complexes. These structures reveal a unique NADP+ binding mode in which the nicotinamide ring is not parallel to the flavin isoalloxazine ring, but lies against it at an angle of approximately 30 degrees, with the C4 atom 3 A from the flavin N5 atom.

Molecular cloning and expression analysis of the Rhodobacter capsulatus sodB gene, encoding an iron superoxide dismutase

Genetic complementation of a sodA sodB Escherichia coli mutant strain was used to clone Rhodobacter capsulatus genes involved in detoxification of superoxide radicals. After sequence analysis, 1 of the 16 identical clones obtained by this selection procedure was shown to contain an open reading frame with sequence similarity to that coding for Fe-containing superoxide dismutases (SodB). The R. capsulatus sodB gene was expressed in E. coli, and the nature of the metal ligand was confirmed by inhibitor sensitivity assays with lysates from both bacterial species. Activity staining of cleared Rhodobacter lysates resolved by polyacrylamide gel electrophoresis indicated that SodB was the only superoxide dismutase present in this phototrophic organism. The sodB gene was expressed at low levels in R. capsulatus cells grown under anaerobic or semiaerobic conditions, but expression was strongly induced upon exposure of the bacteria to air or to methyl viologen. Attempts to construct a sodB mutant in this organism by allelic exchange of the chromosomal copy of the gene with a suicide plasmid containing a mutated sodB gene were unsuccessful, strongly suggesting that the encoded superoxide dismutase is essential for viability of R. capsulatus in aerobic cultures.

Cooperation of the DnaK and GroE chaperone systems in the folding pathway of plant ferredoxin-NADP+ reductase expressed in Escherichia coli

The DnaK system is required for the productive folding of pea chloroplast ferredoxin-NADP+ reductase (FNR) expressed in Escherichia coli. The formation of a mature active enzyme was severely impaired in E. coli dnaK, dnaJ or grpE mutants expressing either the cytosolic precursor of the reductase (preFNR) or the mature apoenzyme, and these forms aggregated extensively in these cells. Coexpression of dnaK from a multicopy plasmid in the dnaK-null mutants restored preFNR processing and folding of FNR, rendering a mature-sized active enzyme. Overexpression of GroESL chaperonins failed to prevent preFNR aggregation, but it restored productive folding of FNR in dnaK-null mutants expressing the mature enzyme. Expression of preFNR in OmpT-protease-deficient E. coli cells resulted in the accumulation of the unprocessed precursor in the soluble fraction of the cells. The interaction of this soluble preFNR, but not the mature reductase, with DnaK and GroEL was evidenced by immunoprecipitation studies. We conclude that, in addition to the GroE chaperonins [Carrillo, N., Ceccarelli, E. A., Krapp, A. R., Boggio, S., Ferreyra, R. G. & Viale, A. M. (1992) J. Biol. Chem. 267, 15537-15541], the DnaK chaperone system plays a crucial role in the folding pathway of FNR.

Oxidative stress causes ferredoxin-NADP+ reductase solubilization from the thylakoid membranes in methyl viologen-treated plants

The flavoenzyme ferredoxin-NADP+ reductase (FNR) is a member of the cellular defense barrier against oxidative damage in Escherichia coli. We evaluated the responses of chloroplast FNR to methyl viologen, a superoxide radical propagator, in wheat (Triticum aestivum L.) plants and chloroplasts. Treatments with the herbicide showed little effect on the levels of FNR protein or transcripts, indicating that expression of this reductase is not upregulated by oxidants in plants. Viologens and peroxides caused solubilization of active FNR from the thylakoids into the stroma, converting the enzyme from a membrane-bound NADPH producer to a soluble NADPH consumer. This response appeared specific for FNR, since other thylakoid proteins were unaffected by the treatments. The reductase-binding protein was released together with FNR, suggesting that it might be the target of oxidative modification. Stromal accumulation of a functional NADPH reductase in response to oxidative stress is formally analogous to the induction of FNR synthesis observed in E. coli under similar conditions. FNR solubilization may be playing a crucial role in maintaining the NADPH/NADP+ homeostasis of the stressed plastid. The unchecked accumulation of NADPH might otherwise increase the risks of oxidative damage through a rise in the Mehler reaction rates and/or the production of hydroxyl radicals.

The role of ferredoxin-NADP+ reductase in the concerted cell defense against oxidative damage -- studies using Escherichia coli mutants and cloned plant genes

Ferredoxin-NADP+ reductases (FNR) participate in cellular defense against oxidative damage. Escherichia coli mutants deficient in FNR are abnormally sensitive to methyl viologen and hydrogen peroxide. Tolerance to these oxidants was regained by expression of plant FNR, superoxide dismutase, or catalase genes in the mutant cells. FNR contribution to the concerted defense against viologen toxicity under redox-cycling conditions was similar to that of the two major E. coli superoxide dismutases together, as judged by the phenotypes displayed by relevant mutant strains. However, FNR expression in sodA sodB strains failed to increase their tolerance to viologens, indicating that the FNR target is not the superoxide radical. Sensitivity of FNR-deficient cells to oxidants is related to extensive DNA damage. Incubation of the mutant bacteria with iron chelators or hydroxyl radical scavengers provided significant protection against viologens or peroxide, suggesting that oxidative injury in FNR-deficient cells was mediated by intracellular iron through the formation of hydroxyl radicals in situ. The NADP(H)-dependent activities of the reductase were necessary and sufficient for detoxification, without participation of either ferredoxin or flavodoxin in the process. Possible mechanisms by which FNR may exert its protective role are discussed.

Plant-type ferredoxin-NADP+ reductases: a basal structural framework and a multiplicity of functions

Ferredoxin-NADP+ (oxido)reductase (EC 1.18.1.2, FNR) is an FAD-containing enzyme that catalyzes the reversible electron transfer between NADP(H) and electron carrier proteins such as ferredoxin and flavodoxin. Isoforms of this flavoprotein are present in chloroplasts, mitochondria, and bacteria in which they participate in a wide variety of redox metabolic pathways. Although ferredoxin-NADP+ reductases have been thoroughly investigated and their properties reviewed on several occasions, considerable advances in the understanding of these flavoenzymes have occurred in the last few years, including the characterization of cDNA and genomic clones encoding FNR proteins from plants, algae, vertebrates, and bacteria, determination of the atomic structure of a plant FNR at high resolution, and the expression of functional reductases in microorganisms like Escherichia coli and Saccharomyces cerevisiae. The aim of this article is to summarize information gained through these recent developments, including the phylogenetic relationships among ferredoxin reductases and the key structural features of the plant FNR family. Other aspects such as the catalytic mechanism of FNR and the molecular events underlying biogenesis, intracellular sorting, folding, and holoenzyme assembly of this important flavoenzyme are also discussed in some detail. Ferredoxin-NADP+ reductases display several outstanding properties that make them excellent model proteins to address broad biological questions.

[Comparison of the sensitivity and specificity of the electrocardiography criteria for left ventricular hypertrophy according to the methods of Romhilt-Estes, Sokolow-Lyon, Cornell and Rodríguez Padial]

INTRODUCTION AND OBJECTIVES

Because left ventricular mass is associated with an increase in the risk of morbidity and mortality of cardiovascular diseases in the general population having the electrocardiogram as an accessible and inexpensive method for the diagnosis of left ventricular hypertrophy, we decided to calculate the sensitivity and specificity of 5 electrocardiographic criteria for the diagnosis of left ventricular hypertrophy and to compare the results of the original authors to ours.

PATIENTS AND METHODS

135 patients were evaluated; 46 patients were excluded by the following criteria: chronic obstructive pulmonary disease, complete left or right bundle branch block, cardiovascular ischemic disease or Wolf-Parkinson-White Syndrome. 89 patients remained and had an electrocardiogram performed applying the following criteria: Romhilt-Estes Point-Score system. Sokolow-Lyon (SV1 + RV5 or V6 > 3.5 mV) and (RaVL > 1.1 mV), Cornell and Rodríguez Padial. Left ventricular hypertrophy was defined by the Penn Convention Criteria.

RESULTS

In our study we obtained the following results: a) Romhilt-Estes had a sensitivity of 12% and a specificity of 87%; b) Sokolow-Lyon (SV1 + RV5 or V6) had a sensitivity of 22% and a specificity of 79%; c) Sokolow-Lyon (RaVL) has a sensitivity of 18% and a specificity of 92%; d) Cornel had a sensitivity of 31% and a specificity of 87%, and e) Rodríguez Padial had a sensitivity of 82% and a specificity of 8%. There are similarities between our results and the authors's original ones. However, there are significant statistical differences between them (p < or = 0.01).

CONCLUSION

Our conclusion is that these criteria have a low diagnostic value in the isolated interpretation of patients with left ventricular hypertrophy, and we need to integrate them with the whole medical history and physical examination.

Conformational requirements of a recombinant ferredoxin-NADP+ reductase precursor for efficient binding to and import into isolated chloroplasts

The cytosolic precursor of the chloroplast flavoprotein ferredoxin-NADP+ reductase was expressed in Escherichia coli rendering a soluble protein that contained bound FAD and could be imported by isolated chloroplasts. The mechanism of plastid translocation was studied under defined conditions using this recombinant precursor holoprotein and intact pea chloroplasts. The first step in the import pathway, namely, binding of the reductase precursor to isolated chloroplasts, was saturable at about 2000 molecules/plastid, and showed a high-affinity interaction with a dissociation constant Kd of approximately 5 nM. Binding was not affected by the addition of soluble leaf extracts or by prior denaturation of the precursor with urea. Analysis of the initial import rates at different precursor concentrations indicated the existence of a single translocation system for this protein. Inclusion of leaf extracts in the assay resulted in a three-fold increase of the maximal import rates to 14,000 molecules . min-(1).chloroplast-(1), with a concomitant decrease in the apparent Km for the recombinant precursor, from 1 microM to 100-150 nM. Comparison of Km and Kd values under various conditions indicated that the binding step of the translocation process is largely irreversible, favouring import and processing. In the absence of extract, a denatured precursor obtained by incubation with urea was a better substrate for plastid import than the holoprotein. Treatment of the precursor with either extract or urea resulted in similar increases in import efficiency (V/Km), suggesting that stimulation by leaf extracts is probably related to unfolding of the precursor prior to translocation.

Epidemic cholera in Guatemala, 1993: transmission of a newly introduced epidemic strain by street vendors

Epidemic cholera reached Guatemala in July 1991. By mid-1993, Guatemala ranked third in the hemisphere in reported cases of cholera. We conducted a case-control study with two age-, sex-, and neighbourhood-matched controls per patient in periurban Guatemala City. Twenty-six patients hospitalized for cholera and 52 controls were enrolled. Seven (47%) of 15 stool cultures obtained after admission yielded toxigenic Vibrio cholerae O1. All seven were resistant to furazolidone, sulfisoxazole, and streptomycin, and differed substantially by pulsed-field gel electrophoresis from the Latin American epidemic strain dominant in the hemisphere since 1991. In univariate analysis, illness was associated with consumption of left-over rice (odds ratio [OR] = 7.0, 95% confidence interval [CI] = 1.4-36), flavored ices (-helados') (OR = 3.6, CI = 1.1 - 12), and street-vended non-carbonated beverages (OR = 3.8, CI = 1.2-12) and food items (OR = 11.0, CI = 2.3-54). Street-vended food items remained significantly associated with illness in multivariate analysis (OR = 6.5, CI = 1.4-31). Illness was not associated with drinking municipal tap water. Maintaining water safety is important, but slowing the epidemic in Guatemala City and elsewhere may also require improvement in street vendor food handling and hygiene.

Contribution of the FAD binding site residue tyrosine 308 to the stability of pea ferredoxin-NADP+ oxidoreductase

The contribution made by tyrosine 308 to the stability of pea ferredoxin-NADP+ reductase was investigated using site-directed mutagenesis. The phenol side chain of the invariant carboxyl terminal tyrosine is stacked coplanar to the isoalloxazine moiety of the FAD cofactor. Fluorescence measurements indicate that this interaction plays a significant role in FAD fluorescent quenching by the reductase apoprotein. Replacement of the tyrosine by tryptophan or phenylalanine caused only a minor increase in the quantum yields of bound FAD, whereas nonaromatic substitutions to serine and glycine resulted in a large fluorescent rise. Results from NADP+ titration experiments support a recent hypothesis [Karplus et al. (1991) Science 251, 60-66], suggesting that the phenol ring of Tyr 308 may fill the nicotinamide binding pocket in the absence of the nucleotide. The stability of the site-directed mutants, judged by thermal- and urea-induced denaturation studies, was lowered with respect to the wild-type enzyme. FNR variants harboring nonaromatic substitutions displayed more extensive destabilization. The decrease in thermodynamic stability correlated with the impairment of catalytic activities [Orellano et al. (1993) J. Biol. Chem 268, 19267-19273]. The results indicate that the presence of the electron-rich aromatic side chain adjacent to the isoalloxazine ring is essential for maximum stabilization of the FNR holoenzyme, resulting in a flavin conformation which optimizes electron flow between the prosthetic group and its redox partners.

The precursor of pea ferredoxin-NADP+ reductase synthesized in Escherichia coli contains bound FAD and is transported into chloroplasts

The precursor of the chloroplast flavoprotein ferredoxin-NADP+ reductase from pea was expressed in Escherichia coli as a carboxyl-terminal fusion to glutathione S-transferase. The fused protein was soluble, and the precursor could be purified in a few steps involving affinity chromatography on glutathione-agarose, cleavage of the transferase portion by protease Xa, and ion exchange chromatography on DEAE-cellulose. The purified prereductase contained bound FAD but displayed marginally low levels of activity. Removal of the transit peptide by limited proteolysis rendered a functional protease-resistant core exhibiting enzymatic activity. The FAD-containing precursor expressed in E. coli was readily transported into isolated pea chloroplasts and was processed to the mature size, both inside the plastid and by incubation with stromal extracts in a plastid-free reaction. Import was dependent on the presence of ATP and was stimulated severalfold by the addition of plant leaf extracts.

Functional complementation of the mvrA mutation of Escherichia coli by plant ferredoxin-NADP+ oxidoreductase

Escherichia coli cells carrying the mvrA mutation are unable to grow aerobically in the presence of the radical propagator methyl viologen (MV). Resistance against MV toxicity could be restored by the introduction of cloned DNA sequences encoding pea chloroplast ferredoxin-NADP+ reductase (FNR), a member of a class of flavoenzymes involved in redox pathways in bacteria, plants and animals. Complementation was strictly dependent on the accumulation of a functional transgenic FNR, since mutated reductases showing decreased enzymatic activities only partially rescued the MV-resistant phenotype. These results support recent observations suggesting that the E. coli mvrA gene encodes a ferredoxin (flavodoxin)-NADP+ reductase (V. Bianchi et al. (1993) J. Bacteriol. 175, 1590-1595). The mvrA mutant cells showed a moderate decrease in the flavodoxin-dependent activation of enzymes essential for anaerobic growth of E. coli. This effect is prevented by expression of a functional pea FNR in the mutant cells.

One-step purification of plant ferredoxin-NADP+ oxidoreductase expressed in Escherichia coli as fusion with glutathione S-transferase

Complementary DNA sequences encoding the mature form of pea ferredoxin-NADP+ reductase were cloned in-frame at the 3' end of the Schistosoma japonicum glutathione S-transferase gene in the expression vector pGEX-3X (Smith and Johnson, Gene 67, 31-40, 1988). A spacer sequence linking the two genes was modified to provide a proteolytic site just before the first amino acid residue of mature pea reductase. When introduced into competent Escherichia coli cells and induced, the resulting plasmid (pGF205) directed the expression of a 60-kDa immunoreactive peptide that results from the fusion between glutathione S-transferase and ferredoxin-NADP+ reductase sequences. The fused protein could be purified in a single step by selective absorption onto glutathione-agarose beads, followed by elution with free glutathione. It showed both transferase and reductase activities. Removal of the transferase portion by cleavage with the restriction protease Xa rendered ferredoxin-NADP+ reductase electrophoretically homogeneous. The purified transgenic enzyme showed kinetic and spectroscopic properties that were similar to those reported for the plant flavoprotein, indicating that, even when fused to the 27-kDa transferase portion, the reductase was still able to assemble FAD and to acquire an active conformation in the bacterial host. The expression-purification protocol employed here allows the isolation of up to 1 mg of active ferredoxin-NADP+ reductase/g of transformed cells. The system is potentially useful for the purification of activity-impaired forms of the flavoprotein.

Probing the role of the carboxyl-terminal region of ferredoxin-NADP+ reductase by site-directed mutagenesis and deletion analysis

The carboxyl-terminal region of plant ferredoxin-NADP+ reductases is formed by an invariant alpha-helix/loop/beta-strand, culminating in a conserved tyrosine that displays extensive interaction with the prosthetic group FAD. We have investigated the potential role of the terminal region in reductase function, by introducing mutations and deletions on pea ferredoxin-NADP+ reductase overexpressed in Escherichia coli. Replacement of the terminal tyrosine by tryptophan, phenylalanine, serine, and glycine resulted in a 2.2-, 2.0-, 22-, and 302-fold reduction, respectively, in kcat for the diaphorase reaction, whereas elimination of the tyrosine caused a 846-fold decrease in kcat. Km values were largely unaffected by the substitutions. Similar results were obtained when the mutants were assayed for cytochrome c reduction, indicating that aromaticity is the most important factor to the function of the tyrosine in catalysis. The presence of the phenol ring at the carboxyl-terminal position of wild-type reductase is important, but not an absolute requirement for enzyme function or FAD assembly. Deletion of the alpha-helix/beta-strand region prevented reductase proper folding in the bacterial host, while shortening of the terminal region by splicing 3 amino acids at the beginning of the alpha-helix produced a moderately soluble reductase, devoid of FAD and enzymatic activity.

Constitutive Transcription and Stable RNA Accumulation in Plastids during the Conversion of Chloroplasts to Chromoplasts in Ripening Tomato Fruits

The size distribution of plastid transcripts during chromoplast differentiation in ripening tomato (Lycopersicon esculentum L.) fruits was determined using northern blot analysis. Hybridization of total cellular RNA from leaves and fruits with several tobacco chloroplast DNA probes showed distinct transcript patterns in chloroplasts and chromoplasts. We also compared transcriptional rates by probing immobilized DNA fragments of small size (representing about 85% of the plastid genome) with run-on transcripts from tomato plastids. The relative rates of transcription of the various DNA regions were very similar in chloro- and chromoplasts. Parallel determination of the steady-state levels of plastid RNA showed no strict correlation between synthesis rate and RNA accumulation. Differences in the relative abundance of transcripts between chloro- and chromoplasts were not very pronounced and were limited to a small number of genes. The results indicate that the conversion of chloroplasts to chromoplasts at the onset of tomato fruit ripening proceeds with no important variations in the relative transcription rates and with only moderate changes in the relative stability of plastid-encoded transcripts.

Assembly of plant ferredoxin-NADP+ oxidoreductase in Escherichia coli requires GroE molecular chaperones

We have recently reported the expression in Escherichia coli of an enzymatically competent ferredoxin-NADP+ oxidoreductase from cloned pea genes encoding either the mature enzyme or its precursor protein (Ceccarelli, E. A., Viale, A. M., Krapp, A. R., and Carrillo, N. (1991) J. Biol. Chem. 266, 14283-14287). Processing to the mature form by bacterial protease(s) and FAD assembly occurred in the bacterial cytosol. Expression of ferredoxin-NADP+ reductase in chaperonin-deficient (groE-) mutants of E. coli resulted in partial reductase assembly at permissive growth temperatures (i.e. 30 degrees C), and in total breakdown of holoenzyme assembly, and accumulation as aggregated inclusion bodies at non-permissive temperatures (i.e. 42 degrees C). Coexpression in these mutants of a cloned groESL operon from the phototrophic bacterium Chromatium vinosum resulted in partial or total recoveries of ferredoxin-NADP+ reductase assembly. The overall results indicate that bacterial chaperonins are required for the productive folding/assembly of eucaryotic ferredoxin-NADP+ reductase expressed in E. coli.

Evaluation of the Extent of Homologous Chloroplast DNA Sequences in the Mitochondrial Genome of Cowpea (Vigna unguiculata L.)

Southern blot hybridization techniques were used to estimate the extent of chloroplast DNA sequences present in the mitochondrial genome of cowpea (Vigna unguiculata L.) The entire mitochondrial chromosome was homogeneously labeled and used to probe blotted DNA fragments obtained by extensive restriction of the tobacco chloroplast genome. The strongest cross-homologies were obtained with fragments derived from the inverted repeat and the atpBE cluster regions, although most of the clones tested (spanning 85% of the tobacco plastid genome) hybridized to mitochondrial DNA. Homologous chloroplast DNA restriction fragments represent a total of 30 to 68 kilobase pairs, depending upon the presence or absence of tRNA-encoding fragments. Plastid genes showing homology with mitochondrial DNA include those encoding ribosomal proteins, RNA polymerase, subunits of photosynthetic complexes, and the two major rRNAs.

Expression, assembly, and processing of an active plant ferredoxin-NADP+ oxidoreductase and its precursor protein in Escherichia coli

The flavoprotein ferredoxin-NADP+ reductase (FNR) catalyzes the final step of the photosynthetic electron transport chain, i.e. the reduction of NADP+ by ferredoxin. A cloned FNR cDNA from a pea library (Newman, B., and Gray, J. (1988) Plant Mol. Biol. 10, 511-520) was used to construct plasmids which express the apoenzyme in Escherichia coli. Two recombinant vectors were prepared, one containing the sequence corresponding to the mature enzyme and another including, in addition, the sequence of the transit peptide that directs FNR to the chloroplast. These proteins were expressed as fusion products to the NH2-terminal portion of beta-galactosidase. In both cases, a 35-kDa immunoreactive polypeptide was the major product, suggesting that the proteins were processed in vivo. NH2-terminal sequence determination of the purified recombinant proteins indicate cleavage at positions -1/-2 with respect to the normal processing site in chloroplasts. The processed enzymes showed enzymatic activities and spectral properties that were similar or identical to those of native plant FNR. When a La protease-deficient E. coli strain was used as a host, the expressed FNR precursor was found to be poorly processed, associated to bacterial pellets, and showed no detectable FNR activity. The overall results indicate that acquisition of the native enzyme conformation and assembly of the prosthetic group takes place in the bacterial host, generating an enzyme that is, as far as studied, indistinguishable from plant FNR.

Chromoplast formation during tomato fruit ripening. No evidence for plastid DNA methylation

Ripening of tomato fruits involves differentiation of chloroplasts into non-photosynthetic chromoplasts. Plastid DNAs isolated either from green leaf chloroplasts or mature red fruit chromoplasts were compared by restriction endonuclease and DNA/DNA hybridization analyses. The same restriction and gene maps were obtained for both types of DNAs, illustrating the lack of major recombinational events during chromoplast formation. Several enzymes were used that discriminate the presence of methylated bases in their target sequences (Pst I, Pvu II, Sal I, Mbo I/Sau 3AI, Msp I/Hpa II, Bst NI/Eco RII). Plastid DNA fragments generated by these enzymes were hybridized against DNA probes encompassing about 85% of the tobacco chloroplast genome. These probes represented genes that follow very different expression behaviors in response to plastid development. Extensive restriction and hybridization analyses failed to reveal any difference between the chloroplast and chromoplast genomes, indicating that no developmentally related DNA methylation was detected by these methods. The results presented here do not support the hypothesis that selective DNA methylation of the chromoplast genome might play a major role in the transcriptional control of gene expression in these non-photosynthetic plastids.

DNA polymerase activity of tomato fruit chromoplasts

DNA polymerase activity was measured in chromoplasts of ripening tomato fruits. Plastids isolated from young leaves or mature red fruits showed similar DNA polymerase activities. The same enzyme species was present in either chloroplasts or chromoplasts as judged by pH and temperature profiles, sensitivities towards different inhibitors and relative molecular mass (Mr 88 kDa). The activities analyzed showed the typical behaviour of plastid-type polymerases. The results presented here suggest that chromoplast maintain their DNA synthesis potential in fruit tissue at chloroplast levels. Consequently, the sharp decrease of the plastid chromosome transcription observed at the onset of fruit ripening could not be due to limitations in the availability of template molecules. Other mechanisms must be involved in the inhibition of chromoplast RNA synthesis.

[Giant duodenal ulcer]

Giant duodenal ulcers have a high mortality. The clinical, radiological and endoscopic appearance are described. The treatment of choice in patients with giant duodenal ulcer is surgical, the continuous infusion of H-2 blockers is useful before the surgical procedure.

[Echography of post-vagotomy gallbladder emptying]

Truncal vagotomy has been related to an enlargement of the resting volume and impaired contraction of the gallbladder, and an increased incidence of cholelithiasis, changes that are not reported in selective or highly selective vagotomy. We studied 12 patients, 7 with truncal vagotomy, 2 with selective, 1 with highly selective and 1 patient with subtotal gastrectomy alone. We measured the gallbladder volume and contraction sonographically and compared them with normal values. The patients with truncal vagotomy had an increased resting volume and an impaired gallbladder contraction. The patients with selective vagotomy had a normal resting volume but a decreased gallbladder contraction. We also found cholelithiasis in 2 of our patients with truncal vagotomy, for an incidence of 28%, similar to the ones reported by other authors.

Chloroplast DNA replication in vitro: site-specific initiation from preferred templates

An enzyme system prepared from maize chloroplasts catalyzes the synthesis of DNA from maize chloroplast DNA sequences cloned in bacterial plasmids. Cloned maize chloroplast DNA fragments Bam HI 17' (2470 bp) and Eco RI x (1368 bp) have been shown to be preferred templates for in vitro DNA synthesis catalyzed by pea chloroplast DNA polymerase preparations [Gold et al. (1987) Proc. Natl. Acad. Sci. USA 84, 194-198]. Analysis of replicative intermediates indicates that although the template activity of the recombinant plasmid pZmcBam 17' is substantially greater than that of the pZmcEco x, replication in both cases originates from within a 455 bp region which overlaps the two plasmids. The remaining approximately 1500 basepair portion of maize chloroplast BamHI fragment 17' is not more active because it contains additional origins for replication. The overlapping region shows sequence homology with a portion of the Chlamydomonas reinhardtii chloroplast chromosome that contains a replication origin. Replication is shown to proceed bidirectionally within the 455 bp origin region. Recombinant plasmid pZmc 427, which is also active in the in vitro DNA synthesis assay, promoted localized replication initiation within a 1 kbp Bg1II-Eco RI fragment of the chloroplast DNA insert, a region that includes the 3' terminal part of the psbA gene.

Nucleotide sequence of a preferred maize chloroplast genome template for in vitro DNA synthesis

Maize chloroplast DNA sequences representing 94% of the chromosome have been surveyed for their activity as autonomously replicating sequences in yeast and as templates for DNA synthesis in vitro by a partially purified chloroplast DNA polymerase. A maize chloroplast DNA region extending over about 9 kilobase pairs is especially active as a template for the DNA synthesis reaction. Fragments from within this region are much more active than DNA from elsewhere in the chromosome and 50- to 100-fold more active than DNA of the cloning vector pBR322. The smallest of the strongly active subfragments that we have studied, the 1368-base-pair EcoRI fragment x, has been sequenced and found to contain the coding region of chloroplast ribosomal protein L16. EcoRI fragment x shows sequence homology with a portion of the Chlamydomonas reinhardtii chloroplast chromosome that forms a displacement loop [Wang, X.-M., Chang, C.H., Waddell, J. & Wu, M. (1984) Nucleic Acids Res. 12, 3857-3872]. Maize chloroplast DNA fragments that permit autonomous replication of DNA in yeast are not active as templates for DNA synthesis in the in vitro assay. The template active region we have identified may represent one of the origins of replication of maize chloroplast DNA.

Cytochrome b-559 genes from Oenothera hookeri and Nicotiana tabacum show a remarkably high degree of conservation as compared to spinach. The enigma of cytochrome b-559: highly conserved genes and proteins but no known function

Recent data suggest that cytochrome b-559, an intrinsic membrane protein of the oxygen-evolving photosystem II in chloroplasts, is a heme cross-linked heteromeric polypeptide unit (Herrmann et al. 1984, FEBS Lett 176:239-244). The genes for this cytochrome, designated psbE and psbF, have been located on the chloroplast chromosome of Oenothera hookeri and Nicotiana tabacum by hybridization with fragments of the corresponding spinach genes, and characterized. In both cases, the nucleotide sequence discloses 2 uninterrupted reading frames of 83 and 39 codons separated by a few nucleotides, as in spinach. The amber translation stop codon of psbE overlaps the putative ribosome-binding site for psbF in all cases. The predicted molecular weights of the proteins are 9.2 and 4.3 kd, respectively. In each of the three plant species, and the direction of transcription is opposite to that of the gene for cytochrome f which is located distal to the b-559 genes. Comparison of the deduced amino acid sequences with those from the corresponding spinach genes shows 97% homology. The ubiquitous presence and remarkably high degree of structural and functional conservation of this gene cluster supports the hypothesis of a heteromeric assembly and an important functional role for cytochrome b-559.

Biosynthesis of ferredoxin-NADP+ oxidoreductase. Evidence for the formation of a functional preholoenzyme in the cytoplasmic compartment

Biosynthesis of ferredoxin-NADP+ reductase in higher plants was investigated in relation with the mechanism of formation of the holoenzyme. The putative precursor of the flavoprotein, obtained after cell-free translation on a wheat germ extract primed with poly(A)-rich mRNA, was able to spontaneously bind free FAD, rendering a functional prereductase. The newly synthesized preholoenzyme showed diaphorase and cytochrome c reductase activities, an apparent molecular mass of 45 kDa, and contained FAD as the only flavin cofactor. It gave a positive reaction towards antisera against mature ferredoxin-NADP+ reductase. On the other hand, intracellular distribution of flavin-synthesizing enzymes indicates that FAD formation occurs in the cytoplasm; that is, in the same compartment as the site of reductase synthesis. On the basis of the preceding data a model is presented for the biosynthesis of the enzyme in vivo, involving conjugation of the apoprotein with FAD in the cytoplasm, followed by transport of the preholoreductase across the chloroplast envelope to reach its final destiny in the thylakoid membrane.

Isolation and sequencing of an active-site peptide from spinach ferredoxin-NADP+ oxidoreductase after affinity labeling with periodate-oxidized NADP+

Spinach ferredoxin-NADP+ oxidoreductase was inactivated by treatment with 2',3'-dialdehyde NADP+ (periodate-oxidized NADP+), which selectively modifies a lysine residue at the nucleotide-binding domain of the enzyme. The identity of the derivatized residue was ascertained by thin-layer chromatography of the protein hydrolysate. Reductase that had been labeled with periodate-oxidized NADP+ and NaB3H4 was treated with trypsin, and samples of the tryptic digest were subjected to reverse-phase high-performance liquid chromatography. The radioactivity profiles showed modification of one specific peptide. The primary structure of this peptide was found to be Gly-Glu-Lys*-Met-Tyr-Ile-Gln-Thr-Arg, where Lys* represents the derivatized lysine. The sequence obtained corresponds to residues 242-250 in the primary structure of spinach ferredoxin-NADP+ reductase recently reported [Karplus et al. (1984) Biochemistry 23, 6576-6583].

A fast and sensitive micromethod for the manual sequencing of peptides using O-phthalaldehyde as derivatizing reagent

A general procedure for the manual sequencing of peptides using the fluorogenic reagent O-phthalaldehyde (OPA) is described. The method can be applied in two different ways. One of them involves back hydrolysis of the anilinothiazolinones resulting from the Edman degradation of the peptide and subsequent detection of the free amino acids as OPA derivatives. The other is a subtractive analysis in which the amino acid composition of the remaining peptide is determined after each degradation cycle. The direct procedure can be coupled to the subtractive one in order to assure the accuracy of the sequence analysis. The method is fast and simple, and allows determination of 10 pmol of amino acid per cycle using standard reagents and instrumentation. Sensitivity can be greatly enhanced provided that ultrapure chemicals are employed. Small peptides (8-10 residues) were sequenced from 200 pmol sample, using a high-performance liquid chromatography assembly coupled to a fluorescence detector.

Affinity labeling of spinach ferredoxin-NADP+ oxidoreductase with periodate-oxidized NADP+

Periodate-oxidized NADP+ (dialdehyde-NADP+) inactivated soluble ferredoxin-NADP+ oxidoreductase and combined covalently to the enzyme. This inactivation was first order with respect to dialdehyde-NADP+ and followed saturation kinetics, indicating that the enzyme initially forms a reversible complex with the inactivator. NADP+ afforded complete protection against inactivation, while spinach ferredoxin was uneffective. In the presence of exogenous ferredoxin and illuminated thylakoids, the nucleotide analog functioned as a coenzyme for the reductase, although with rather lower efficiency than NADP+. It also acted as a competitive inhibitor with respect to NADPH in diaphorase activity. Incorporation of radioactivity from periodate-oxidized [3H]NADP+ gave a stoichiometry of 0.85 mol of reagent/mol of reductase, indicating that the modification of a single residue in the flavoprotein is responsible for the loss of enzymatic activity.

Essential histidyl residues of ferredoxin-NADP+ oxidoreductase revealed by diethyl pyrocarbonate inactivation

Diethyl pyrocarbonate inhibited diaphorase activity of ferredoxin-NADP+ oxidoreductase with a second-order rate constant of 2 mM-1 X min-1 at pH 7.0 and 20 degrees C, showing a concomitant increase in absorbance at 242 nm due to formation of carbethoxyhistidyl derivatives. Activity could be restored by hydroxylamine, and the pH curve of inactivation indicated the involvement of a residue having a pKa of 6.8. Derivatization of tyrosyl residues was also evident, although with no effect on the diaphorase activity. Both NADP+ and NADPH protected the enzyme against inactivation, suggesting that the modification occurred at or near the nucleotide binding domain. The reductase lost all of its diaphorase activity after about two histidine residues had been blocked by the reagent. In differential-labeling experiments with NADP+ as protective agent, it was shown that diaphorase inactivation resulted from blocking of only one histidyl residue per mole of enzyme. Modified reductase did not bind pyridine nucleotides. Modification of the flavoprotein in the presence of NADP+, i.e., with full preservation of diaphorase activity, resulted in a significant impairment of cytochrome c reductase activity, with a second-order rate constant for inactivation of about 0.5 mM-1 X min-1. Reversal by hydroxylamine and spectroscopic data indicated that this second residue was also a histidine. Ferredoxin afforded only slight protection against this inhibition. Conversely, carbethoxylation of the enzyme did not affect complex formation with the ferrosulfoprotein. Redox titration of the modified reductase with NADPH and with reduced ferredoxin suggested that the second histidine might be located in the electron pathway between FAD and ferredoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of ferredoxin-NADP+ oxidoreductase with triazine dyes. A rapid purification method by affinity chromatography

The triazine dyes, Cibacron blue F3GA and Procion red HE3B inhibited diaphorase activity of ferredoxin-NADP+ reductase, in a competitive manner with respect to NADPH. The Ki values were 1.5 and 0.2 microM, respectively. Binding of the dyes to the flavoprotein, as measured by difference spectroscopy, indicated an apparent stoichiometry of 1 mol dye/mol reductase and was prevented by NADP+ or high ionic strength. Chemical modification of a lysine residue and a carboxyl group at the NADP(H) binding site of the enzyme prevented complex formation with Procion red. Procion red showed a higher affinity for ferredoxin-NADP+ reductase than Cibacron blue. The Kd values were 1.9 and 5 microM, respectively. Once covalently linked to a Sepharose matrix, the triazine compounds specifically bind the flavoprotein. The interaction is partially electrostatic and partially hydrophobic. The enzyme can be eluted by high concentrations of salt or low concentrations of the corresponding coenzyme. The use of this affinity column allows the rapid purification of ferredoxin-NADP+ oxidoreductase from spinach leaves with good yields.

Interaction of Ferredoxin-NADP Oxidoreductase with the Thylakoid Membrane

The binding of ferredoxin-NADP reductase to spinach chloroplast membranes was studied by washing the membranes with different media. Release of the enzyme from the thylakoids was greater in 0.75 millimolar EDTA but was not complete inasmuch as 20% the activity remained membrane-bound after three washes.A Scatchard plot of binding experiments suggests the presence of one type of binding site and a stoichiometry of 3 to 4 nanomoles of reductase per micromole of chlorophyll was calculated. Rebinding has a nonspecific requirement for cations. Their effectiveness increased with their valency. Rebinding of purified enzyme to depleted membranes resulted in a stimulation of its diaphorase activity.It is suggested that binding of ferredoxin-NADP reductase to thylakoid membranes is dependent upon neutralization of negative charges.

An essential carboxyl group at the nucleotide binding site of ferredoxin-NADP+ oxidoreductase

Woodward's reagent K (N-ethyl-5-phenylisoxazolium-3'-sulfonate) inactivated both soluble and membrane bound-ferredoxin-NADP+ reductase of spinach chloroplasts. Either NADP+ or NADPh afforded complete protection against modification. Ki and the apparent Kd for protection afforded by NADP+ depended on the ionic strength of the medium. Nucleophylic displacement of reagent bound to the soluble enzyme by [14C]glycine ethyl ester showed that 5 to 6 carboxyl groups/flavin were modified when the diaphorase activity was completely inhibited. In differential labeling experiments using NADP+ as protective agent, it was shown that enzyme inactivation was due to blocking of only 1 carboxyl group/mol. Derivatized reductase did not bind pyridine nucleotides. Protection by NADP+ of the membrane-bound reductase was higher, and the apparent Kd for NADP+ lower, in the light than in the dark. Inactivation increased abruptly with the external pH, indicating a progressive exposure of the carboxyl group as the pH was raised. The results presented suggest (a) the existence of a light-driven conformational change and a pH-dependent transition in membrane-bound ferredoxin-NADP+ reductase; (b) the presence of an essential carboxyl residue in the nucleotide binding site of the reductase.

Light modulation of chloroplast membrane-bound ferredoxin-NADP+ oxidoreductase

Light increases the affinity of chloroplast membrane-bound ferredoxin-NADP+ oxidoreductase for its physiological substrates in NADP+ photoreduction, that is, NADP+ and ferredoxin. Light may cause this effect through a conformational change of the enzyme related to the formation of a light-driven delta pH since the effect is prevented by uncouplers. Although the external pH does influence the extent of photoreduction of NADP+ in saturating light, it does not significantly influence the extent of the energy-driven change in affinity of the enzyme for its substrates.

Effect of Light on Chemical Modification of Chloroplast Ferredoxin-NADP Reductase

Chemical modification of spinach chloroplasts by phenylglyoxal and dansyl chloride resulted in inhibition of NADP photoreduction. The rate of inactivation was higher with both reagents when modification was carried out in the light with methylviologen or phenazine methosulfate present. Uncouplers prevent the effect of light. Electron transport from water to methylviologen was not affected by the modifiers.The presence of 10 millimolar NADP completely protected the membrane-bound reductase against inactivation by phenylglyoxal. With lower concentrations, protection was higher in the light than in the dark. The apparent dissociation constants of the enzyme-substrate complex for NADP were 0.9 and 0.1 millimolar for the dark and light inactivation, respectively. Inactivation of NADP photoreduction by dansyl chloride was completely prevented by ferredoxin, but only partially by nucleotides.The diaphorase activity was inhibited in chloroplasts modified by phenylglyoxal, but not when modified by dansyl chloride.The results suggest that energizing thylakoid membranes by light induces a conformational change in membrane-bound ferredoxin-NADP reductase, and that the reductase is an allotopic enzyme.

[Liver abscess. Diagnosis by the method of opacification]

A 15 min infusion of a 75% iodized solution at 2 cc/k-w produces opacification of the more vascularized organs; hypovascular, necrotic or cystic regions are thus of a different radiological density. In order to show the usefulness of this method in diagnosing a hepatic abscess quickly and topographically, it was applied in 13 cases which had been diagnosed as invading amoebiasis. Hepatography proved to be the most valuable. Positive findings are observed 5 to 7 min after infusion has been completed. The greater density at the edge of the abscess enables its diameter to be measured and the liquid content to be calculated fairly accurately.