Free-radical-induced mutation vs redox regulation: costs and benefits of genes in organelles.
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Aging↗
Biomedical subjects
J F Allen
Publications and source records attributed to J F Allen.
Histidine and tyrosine phosphorylation in pea mitochondria: evidence for protein phosphorylation in respiratory redox signalling.
A 37 kDa protein in pea mitochondria was found to contain phosphorylated residues. Phosphorylation was acid-labile but stable in alkali solution, a unique property of phosphorylation on histidine, indicating that a signal transduction pathway with homology to bacterial two-component systems might exist in plant mitochondria. We also describe the first example of tyrosine phosphorylation in plant organelles and the first indication of protein phosphorylation as part of a redox signalling mechanism in mitochondria. Labelling of three proteins (28, 27 and 12 kDa) was found to be dependent on the redox state of the reaction medium. Their phospho-groups were resistant to alkali as well as acid treatment and labelling was inhibited by the tyrosine kinase inhibitor genistein.
Histidine↗
Photosynthesis. Regulation by redox signalling.
Photosynthesis is light-driven redox chemistry. Molecular redox signalling, the coupling of gene expression to electron transfer, is now implicated in the adaptation of photosynthesis to variation in light quality and quantity.
Bacterial Proteins↗
Patient with craniosynostosis and marfanoid phenotype (Shprintzen-Goldberg syndrome) and cloverleaf skull.
Marfanoid phenotype with craniosynostosis (Shprintzen-Goldberg syndrome) is a rare disorder previously described in only 5 patients. We report on the sixth known patient with this condition. The findings which distinguish our patient from others reported previously are that she was ascertained prenatally as having a cloverleaf skull; this is the first female patient described with this condition. Postnatally, she presented with arachnodactyly, camptodactyly, and clover-leaf skull. Imaging studies of the brain documented microcephaly with malformed brain, hydrocephaly, and hypoplasia of the corpus callosum. She also had choanal atresia and stenosis, a clinical finding previously reported only once, in this disorder.
Abnormalities, Multiple↗
Substrate specificity and kinetics of thylakoid phosphoprotein phosphatase reactions.
A synthetic 15-amino-acid phosphopeptide analogue of an N-terminal phosphorylated segment of LHC II was found to inhibit dephosphorylation not only of phospho-LHC II but of all other thylakoid phosphoproteins resolved by phosphorimaging. The results suggest that structural features required for recognition of the phosphoprotein phosphatase are common to different thylakoid phosphoproteins as well as to the phosphopeptide itself: at least one thylakoid phosphoprotein phosphatase exhibits a broad substrate specificity. Dephosphorylation reaction rates of all 13 thylakoid phosphoproteins were determined, and the dephosphorylation half-times were found to range from 7 min to more than 180 min. Most of the phosphoprotein dephosphorylation reactions were partially inhibited by NaF, and were insensitive to antimycin A and okadaic acid. Nevertheless, both antimycin A and NaF stimulated the phosphorylation of LHC II and 9 kDa protein. Possible reasons for differences in sensitivity to these inhibitors are discussed.
Amino Acid Sequence↗
Partial purification of a cyanobacterial membrane protein with amino terminal sequence similarity to the N-methylphenylalanine pilins.
Cyanobacterial pilin was extracted from Synechococcus 6301 membranes using a detergent mixture comprising 1% Triton X-100, 1% Thesit and 0.5% dodecyl beta-D-maltoside. Partial purification of pilin from the crude extract was achieved by a single-step purification applying the Rotofor isoelectric focusing system. Up to 100-fold purification of pilin from the crude extract was achieved in a single run. SDS-PAGE analysis showed Synechococcus 6301 pilin migration with an apparent molecular weight of 11 kDa. The amino terminal sequence of the first 28 amino acid residues was identified. Alignment of the predicted sequence showed a 60-80% identity with amino terminal sequences of pilins from pathogenic gram-negative bacteria (enterobacteria). The apparent mass of Synechococcus 6301 pilin was, however, lower. The amino terminus of Synechococcus 6301 pilin, as with other pilins, has a high content of hydrophobic amino acids.
Amino Acid Sequence↗
Control of gene expression by redox potential and the requirement for chloroplast and mitochondrial genomes.
Recent experiments with bacteria have shown that light and oxygen can control gene expression through effects on oxidation-reduction potential. The term "redox sensor" is proposed as a general term for electron carriers that initiate control of gene expression upon oxidation or reduction. The term "redox response regulator" is proposed for DNA-binding proteins that modify gene expression as a result of the action of redox sensors. Redox sensors and redox response regulators may function together in feedback control of redox potential in photosynthesis and respiration, protecting the cell from damage caused by electrochemistry operating on inappropriate electron donors and acceptors. Chloroplast and mitochondrial redox sensors and redox response regulators, themselves encoded in the nucleus, may place expression of chloroplast and mitochondrial genes under redox regulatory control. This hypothesis offers an explanation for the persistence, in evolution, of chloroplast and mitochondrial genomes, and for the constancy of the subset of chloroplast and mitochondrial proteins encoded and synthesized within the organelle.
Animals↗
Chloroplast thylakoid protein phosphatase reactions are redox-independent and kinetically heterogeneous.
At least eleven thylakoid proteins become phosphorylated under reducing conditions, and redox titration has identified a common midpoint potential of Em = +38 +/- 4 mV, n = 0.95 +/- 0.06. In the presence of the phosphatase inhibitor NaF (10 mM), the redox dependency of phosphorylation is found to be essentially unchanged: Em = +50 +/- 3 mV, n = 1.02 +/- 0.04. Thylakoid membranes were phosphorylated in the light and then incubated at various redox potentials for 15 min in the dark; no redox dependency was observed in the dephosphorylation of any of the 17 bands then distinguishable by autoradiography and phosphorimaging. The phosphoprotein phosphatase reactions can be divided arbitrarily into four kinetic classes: the fastest, class I, includes LHC II; the moderate class II includes D1 and D2; the slow class III includes CP43 and the 9 kDa phosphoprotein; finally, a 19.5 kDa protein exhibited no loss of 32P at all. In separate experiments we measured thylakoid protein dephosphorylation initiated by changing the redox potential from -140 to +200 mV, in the presence or absence of fluoride. In this case the results are consistent with at least two kinetically distinguishable classes of phosphoprotein phosphatase reactions. We conclude that thylakoid protein phosphatase reactions are kinetically heterogeneous and redox-independent. It follows that the redox dependency of thylakoid protein phosphorylation is a property of thylakoid protein kinase reactions. Our observed Em and n values are consistent with a primary site of kinase redox control at the level of PQ/PQ(.)- of the Qi (Qn) site of the cytochrome b6/f complex.
Chloroplasts↗
Redox control of transcription: sensors, response regulators, activators and repressors.
In a growing number of cases, transcription of specific genes is known to be governed by oxidation or reduction of electron carriers with which the gene products interact. The biological function of such control is to activate synthesis of appropriate redox proteins, and to repress synthesis of inappropriate ones, in response to altered availability of specific electron sources and sinks. In prokaryotic systems this control appears to operate by two general classes of mechanism: by two-component regulation involving protein phosphorylation on histidine and aspartate; and by direct oxidation-reduction of gene repressors or activators. For the first class, termed 'two-component redox regulation', the term 'redox sensor' is proposed for any electron carrier that becomes phosphorylated upon oxidation or reduction and thereby controls phosphorylation of specific response regulators, while the term 'redox response regulator' is proposed for the corresponding sequence-specific DNA-binding protein that controls transcription as a result of its phosphorylation by one or more redox sensors. For the second class of redox regulatory mechanism, the terms 'redox activator protein' and 'redox repressor protein' are proposed for single proteins containing both electron transfer and sequence-specific DNA-binding domains. The structure, function and biological distribution of these components are discussed.
Amino Acid Sequence↗
Protein phosphorylation and Mg2+ influence light harvesting and electron transport in chloroplast thylakoid membrane material containing only the chlorophyll-a/b-binding light-harvesting complex of photosystem II and photosystem I.
A material containing only photosystem I (PSI) and the chlorophyll-a/b-binding light-harvesting complex of PSII (LHC-II) has been isolated from the chloroplast thylakoid membrane by solubilization with Triton X-100. Fluorescence spectroscopy shows that, within the material, LHC-II is coupled to PSI for excitation-energy transfer and that this coupling is decreased by the presence of Mg2+, which also decreased PSI electron transport specifically at limiting light intensity. Inclusion of phosphorylated LHC-II within the material did not alter its structure, but gave decreased energy transfer to PSI and inhibition of electron transport which was independent of light intensity, implying effects of phosphorylation on both light harvesting and directly on electron transport. Inclusion of Mg2+ within the phosphorylated material gave decreased energy transfer, but slightly increased PSI electron transport. A cation-induced direct promotion of PSI electron transport was also observed in isolated PSI particles. The PSI/LHC-II material represents a model system for examining protein interactions during light-state adaptations and the possibility that LHC-II can contribute to the antenna of PSI in light state 2 in vivo is discussed.
Chlorophyll↗
Protein phosphorylation in regulation of photosynthesis.
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Amino Acid Sequence↗
Cystic hygroma and congenital diaphragmatic hernia: early prenatal sonographic evaluation of Fryns' syndrome.
We report a case of cystic hygroma and diffuse lymphangiectasia detected by sonogram at 12 weeks' gestation. Fetal karyotype was normal. At 20 weeks' gestation, herniation of the bowel into the chest was noted. At delivery, the infant was diagnosed as having Fryns' syndrome. This is the first reported case of Fryns' syndrome presenting with cystic hygroma.
Adult↗
How does protein phosphorylation regulate photosynthesis?
Phosphorylation of light-harvesting antenna proteins redirects absorbed light energy between reaction centres of photosynthetic membranes. A generally accepted explanation for this is that electrostatic forces drive the more negatively charged, phosphorylated antenna proteins between membrane domains that differ in surface charge. However, structural studies on soluble phosphoproteins indicate that phosphorylated amino acid side chains have specific effects on molecular recognition, by ligand blocking or by intramolecular interactions which alter protein structure. These studies suggest alternative mechanisms for phosphorylation in control of pairwise protein-protein interactions in biological membranes. Thus, in photosynthesis, the surface charge model is only one possible interpretation.
Amino Acid Sequence↗
Fetal hemangioma. Sonographic and color flow Doppler findings.
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Adult↗
Photosynthetic electron transport controls nitrogen assimilation in cyanobacteria by means of posttranslational modification of the glnB gene product.
A glnB gene is identified in the cyanobacterium Synechococcus sp. PCC 7942, and its gene product is found to be covalently modified as a result of imbalance in electron transfer in photosynthesis, where photosystem II is favored over photosystem I. The gene was cloned and sequenced and found to encode a polypeptide of 112 amino acid residues, whose sequence shows a high degree of similarity to the Escherichia coli regulatory protein, PII. In E. coli, PII is involved in signal transduction in transcriptional and post-translational regulation of nitrogen assimilation. Increase in ammonium ion concentration is shown to decrease covalent modification of the Synechococcus PII protein, as in enteric bacteria. We therefore propose that the photosynthetic electron transport chain may regulate the pathway of nitrogen assimilation in cyanobacteria by means of posttranslational, covalent modification of the glnB gene product. The existence of the glnB gene in different strains of cyanobacteria is demonstrated and its implications are discussed.
Amino Acid Sequence↗
Cyanobacterial thylakoid membrane proteins are reversibly phosphorylated under plastoquinone-reducing conditions in vitro.
Reversible, light-dependent protein phosphorylation was observed in isolated thylakoid membranes of the cyanobacterium Synechococcus 6301. A polypeptide of 15 kDa in particular was phosphorylated under plastoquinone-reducing conditions and was not phosphorylated under plastoquinone-oxidising conditions. Phosphorylation and dephosphorylation reactions involving this and several other membrane polypeptides showed sensitivity to inhibitors of protein kinases and phosphatases. Changes in phosphorylation state correlated with changes in low temperature fluorescence emission characteristic of changes in excitation energy distribution between the photosystems. The 15 kDa phosphopolypeptide is likely to be involved directly in light state adaptations in cyanobacteria.
Cyanobacteria↗
Modification of a glnB-like gene product by photosynthetic electron transport in the cyanobacterium Synechococcus 6301.
Covalent modification of a 13 kDa soluble-phase protein occurs during adaptation of cells of the cyanobacterium Synechococcus 6301 (mutant AN112) to light specifically absorbed by photosystem II. This adaptation is accompanied by functional changes indicative of altered excitation energy distribution between the photosystems. The 13 kDa protein is identified by solid-phase N-terminal sequencing as a protein related to PII, the glnB gene product of E. coli. In E. coli, the PII protein undergoes uridylylation and acts as a regular of glutamine synthetase at both the post-translational and transcriptional levels. The implications of modification of a transcriptional regulator by photosynthetic electron transport are discussed.
Amino Acid Sequence↗
Response of the Photosynthetic Apparatus in Dunaliella salina (Green Algae) to Irradiance Stress.
The response of the photosynthetic apparatus in the green alga Dunaliella salina, to irradiance stress was investigated. Cells were grown under physiological conditions at 500 millimoles per square meter per second (control) and under irradiance-stress conditions at 1700 millimoles per square meter per second incident intensity (high light, HL). In control cells, the light-harvesting antenna of photosystem I (PSI) contained 210 chlorophyll a/b molecules. It was reduced to 105 chlorophyll a/b in HL-grown cells. In control cells, the dominant form of photosystem II (PSII) was PSII(alpha)(about 63% of the total PSII) containing >250 chlorophyll a/b molecules. The smaller antenna size PSII(beta) centers (about 37% of PSII) contained 135 +/- 10 chlorophyll a/b molecules. In sharp contrast, the dominant form of PSII in HL-grown cells accounted for about 95% of all PSII centers and had an antenna size of only about 60 chlorophyll a molecules. This newly identified PSII unit is termed PSII(gamma). The HL-grown cells showed a substantially elevated PSII/PSI stoichiometry ratio in their thylakoid membranes (PSII/PSI = 3.0/1.0) compared to that of control cells (PSII/PSI = 1.4/1.0). The steady state irradiance stress created a chronic photoinhibition condition in which D. salina thylakoids accumulate an excess of photochemically inactive PSII units. These PSII units contain both the reaction center proteins and the core chlorophyll-protein antenna complex but cannot perform a photochemical charge separation. The results are discussed in terms of regulatory mechanism(s) in the plant cell whose function is to alleviate the adverse effect of irradiance stress.
Journal Article↗