PubMed Health⌕ Search

Biomedical subjects

F Kessler

Publications and source records attributed to F Kessler.

At least 19 recordsLinked to original sources
PubMed2001

FLU: a negative regulator of chlorophyll biosynthesis in Arabidopsis thaliana.

Tetrapyrroles such as chlorophylls and bacteriochlorophylls play a fundamental role in the energy absorption and transduction activities of photosynthetic organisms. Because of these molecules, however, photosynthetic organisms are also prone to photooxidative damage. They had to evolve highly efficient strategies to control tetrapyrrole biosynthesis and to prevent the accumulation of free intermediates that potentially are extremely destructive when illuminated. In higher plants, the metabolic flow of tetrapyrrole biosynthesis is regulated at the step of delta-aminolevulinic acid synthesis. This regulation previously has been attributed to feedback control of Glu tRNA reductase, the first enzyme committed to tetrapyrrole biosynthesis, by heme. With the recent discovery of chlorophyll intermediates acting as signals that control both nuclear gene activities and tetrapyrrole biosynthesis, it seems likely that heme is not the only regulator of this pathway. A genetic approach was used to identify additional factors involved in the control of tetrapyrrole biosynthesis. In Arabidopsis thaliana, we have found a negative regulator of tetrapyrrole biosynthesis, FLU, which operates independently of heme and seems to selectively affect only the Mg(2+) branch of tetrapyrrole biosynthesis. The identity of this protein was established by map-based cloning and sequencing the FLU gene. FLU is a nuclear-encoded plastid protein that, after import and processing, becomes tightly associated with plastid membranes. It is unrelated to any of the enzymes known to be involved in tetrapyrrole biosynthesis. Its predicted features suggest that FLU mediates its regulatory effect through interaction with enzymes involved in chlorophyll synthesis.

Amino Acid Sequence↗
PubMed2001

Targeting of an abundant cytosolic form of the protein import receptor at Toc159 to the outer chloroplast membrane.

Chloroplast biogenesis requires the large-scale import of cytosolically synthesized precursor proteins. A trimeric translocon (Toc complex) containing two homologous GTP-binding proteins (atToc33 and atToc159) and a channel protein (atToc75) facilitates protein translocation across the outer envelope membrane. The mechanisms governing function and assembly of the Toc complex are not yet understood. This study demonstrates that atToc159 and its pea orthologue exist in an abundant, previously unrecognized soluble form, and partition between cytosol-containing soluble fractions and the chloroplast outer membrane. We show that soluble atToc159 binds directly to the cytosolic domain of atToc33 in a homotypic interaction, contributing to the integration of atToc159 into the chloroplast outer membrane. The data suggest that the function of the Toc complex involves switching of atToc159 between a soluble and an integral membrane form.

Arabidopsis↗
PubMed2001

Molecular biology of chloroplast biogenesis: gene expression, protein import and intraorganellar sorting.

The chloroplast is the hallmark organelle of plants. It performs photosynthesis and is therefore required for photoautotrophic plant growth. The chloroplast is the most prominent member of a family of related organelles termed plastids which are ubiquitous in plant cells. Biogenesis of the chloroplast from undifferentiated proplastids is induced by light. The generally accepted endosymbiont hypothesis states that chloroplasts have arisen from an internalized cyanobacterial ancestor. Although chloroplasts have maintained remnants of the ancestral genome (plastome), the vast majority of the genes encoding chloroplast proteins have been transferred to the nucleus. This poses two major challenges to the plant cell during chloroplast biogenesis: First, light and developmental signals must be interpreted to coordinately express genetic information contained in two distinct compartments. This is to ensure supply and stoichiometry of abundant chloroplast components. Second, developing chloroplasts must efficiently import nuclear encoded and cytosolically synthesized proteins. A subset of proteins, including such encoded by the plastome, must further be sorted to the thylakoid compartments for assembly into the photosynthetic apparatus.

Biological Transport↗
PubMed2001

Molecular characterization of tomato 3-dehydroquinate dehydratase-shikimate:NADP oxidoreductase.

Analysis of cDNAs encoding the bifunctional 3-dehydroquinate dehydratase-shikimate:NADP oxidoreductase (DHQase-SORase) from tomato (Lycopersicon esculentum) revealed two classes of cDNAs that differed by 57 bp within the coding regions, but were otherwise identical. Comparison of these cDNA sequences with the sequence of the corresponding single gene unequivocally proved that the primary transcript is differentially spliced, potentially giving rise to two polypeptides that differ by 19 amino acids. Quantitative real-time polymerase chain reaction revealed that the longer transcript constitutes at most 1% to 2% of DHQase-SORase transcripts. Expression of the respective polypeptides in Escherichia coli mutants lacking the DHQase or the SORase activity gave functional complementation only in case of the shorter polypeptide, indicating that skipping of a potential exon is a prerequisite for the production of an enzymatically active protein. The deduced amino acid sequence revealed that the DHQase-SORase is most likely synthesized as a precursor with a very short (13-amino acid) plastid-specific transit peptide. Like other genes encoding enzymes of the prechorismate pathway in tomato, this gene is elicitor-inducible. Tissue-specific expression resembles the patterns obtained for 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase 2 and dehydroquinate synthase genes. This work completes our studies of the prechorismate pathway in that cDNAs for all seven enzymes (including isozymes) of the prechorismate pathway from tomato have now been characterized.

3' Untranslated Regions↗
PubMed2001

Protein translocon at the Arabidopsis outer chloroplast membrane.

Chloroplasts are organelles essential for the photoautotrophic growth of plants. Their biogenesis from undifferentiated proplastids is triggered by light and requires the import of hundreds of different precursor proteins from the cytoplasm. Cleavable N-terminal transit sequences target the precursors to the chloroplast where translocon complexes at the outer (Toc complex) and inner (Tic complex) envelope membranes enable their import. In pea, the Toc complex is trimeric consisting of two surface-exposed GTP-binding proteins (Toc159 and Toc34) involved in precursor recognition and Toc75 forming an aequeous protein-conducting channel. Completion of the Arabidopsis genome has revealed an unexpected complexity of predicted components of the Toc complex in this plant model organism: four genes encode homologs of Toc159, two encode homologs of Toc34, but only one encodes a likely functional homolog of Toc75. The availability of the genomic sequence data and powerful molecular genetic techniques in Arabidopsis set the stage to unravel the mechanisms of chloroplast protein import in unprecedented depth.

Arabidopsis↗
PubMed2000

Interactions of inflammatory mediators and low pH not influenced by capsazepine in rat cutaneous nociceptors.

The rat skin-saphenous nerve preparation was used to record from mechano-heat sensitive C-fibers whose receptive fields were superfused with various solutions of low pH and of bradykinin, serotonin and prostaglandin E2. Only synchronous application of protons and mediators resulted in a significant nearly three-fold augmentation of the nociceptive pH response, and capsazepine (10(-5) M) did not block this short-lived enhancement. Thus, it does not seem to involve the capsaicin receptor (VRI) which is in contrast to a previous finding from cultured sensory neurons.

Animals↗
PubMed2000

The major protein import receptor of plastids is essential for chloroplast biogenesis.

Light triggers the developmental programme in plants that leads to the production of photosynthetically active chloroplasts from non-photosynthetic proplastids. During this chloroplast biogenesis, the photosynthetic apparatus is rapidly assembled, mostly from nuclear-encoded imported proteins, which are synthesized in the cytosol as precursors with cleavable amino-terminal targeting sequences called transit sequences. Protein translocon complexes at the outer (Toc complex) and inner (Tic complex) envelope membranes recognize these transit sequences, leading to the precursors being imported. The Toc complex in the pea consists of three major components, Toc75, Toc34 and Toc159 (formerly termed Toc86). Toc159, which is an integral membrane GTPase, functions as a transit-sequence receptor. Here we show that Arabidopsis thaliana Toc159 (atToc159) is essential for the biogenesis of chloroplasts. In an Arabidopsis mutant (ppi2) that lacks atToc159, photosynthetic proteins that are normally abundant are transcriptionally repressed, and are found in much smaller amounts in the plastids, although ppi2 does not affect either the expression or the import of less abundant non-photosynthetic plastid proteins. These findings indicate that atToc159 is required for the quantitative import of photosynthetic proteins. Two proteins that are related to atToc159 (atToc120 and atToc132) probably help to maintain basal protein import in ppi2, and so constitute components of alternative, atToc159-independent import pathways.

Amino Acid Sequence↗
PubMed2000

The phenotypic profile of CD34-positive peripheral blood stem cells in different mobilization regimens.

The type of regimen used might result in mobilization of phenotypically and functionally different CD34(+) cells. We compared the phenotype of CD34(+) cells in leukapheresis products of three homogeneous groups: I, healthy individuals treated with granulocyte colony-stimulating factor (G-CSF) alone (n = 13); II, patients mobilized with G-CSF following chemotherapy (n = 16); and III, patients mobilized with G-CSF after high-dose chemotherapeutic pretreatment (n = 24). Multiparameter flow cytometry was performed for CD34(+) subpopulation analysis and focused on adhesion molecules, differentiation markers and megakaryocytic markers relevant for stem cell homing, with special reference to the importance of L-selectin expression. Regimens I and II led to higher numbers of mobilized CD34(+) cells (mean 468 x 10(6) and 491 x 10(6) CD34(+) cells per leukapheresis procedure respectively) than regimen III (mean 41 x 10(6) CD34(+) cells per leukapheresis procedure). Both the expression of L-selectin and CD54 on CD34(+) cells was significantly lower in group III, as was the percentage of megakaryocytic (CD41(+)) progenitors. A higher percentage of primitive (CD38(-) and/or HLA(-)DR(-)) CD34(+) cells was found in group III, correlating with a higher clonogenicity of the CD34(+) cells. However, when comparing the CD34(+)_ subpopulations that were also positive for L-selectin, there was no significant difference between the three regimens. A similar approach for the megakaryocytic CD34+ population resulted in an even worse quality of regimen III: 5.1% of CD34(+) being CD41(+)/L-selectin(+) compared with 9.2% and 8.9% in regimens I and II respectively. We concluded that the phenotypes of the CD34(+) cells in the G-CSF (group I) and G-CSF-chemotherapy (group II) regimens are similar, whereas the phenotype of the CD34(+) cells mobilized in the high-dose regimen (group III) displayed features that might negatively influence homing of the cells. Future studies will be directed towards regimens that will lead to the mobilization of a higher amount of CD34(+) cells with a phenotypically favourable phenotype.

Antigens, CD34↗
PubMed1999

Identification of proteins associated with plastoglobules isolated from pea (Pisum sativum L.) chloroplasts.

Plastoglobules are conspicuous lipid-containing structures in the chloroplast stroma and are thought to serve as lipid reservoirs for thylakoid membranes. Plastoglobules also contain low levels of proteins. We have purified plastoglobules from a pea chloroplast membrane fraction. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the purified plastoglobules revealed more than a dozen distinct polypeptides that we propose to term plastoglobulins. For one of the proteins, termed plastoglobulin 1 (PG1), we have obtained partial N-terminal and internal protein sequences. The amino acid sequence, deduced from cDNA, encoded a precursor protein of a calculated mass of 38,491 Da which contained a 48-residue-long N-terminal signal sequence. Pre-PG1 obtained by coupled in-vitro transcription/translation was imported into pea chloroplasts, its signal sequence was cleaved and mature PG1 was assembled into plastoglobules. Homology searches of the data bases revealed similarity of PG1 to the plastoglobule-associated protein of Capsicum annuum, the carotenoid-associated protein of Cucumis sativus and to a protein of the cyanobacterium Synechocystis sp., indicating that PG1 is a novel member of an ancient protein family. Immunoelectron microscopy using PG1 specific antibodies indicated that PG1 is present in multiple copies on the surface of plastoglobules.

Amino Acid Sequence↗
PubMed1999

Heat-induced release of CGRP from isolated rat skin and effects of bradykinin and the protein kinase C activator PMA.

In the skin, noxious heating induces an axon reflex response which is commonly accepted to be due to the release of vasodilatory neuropeptides from polymodal nociceptors. In the present study, the quantitative assessment of calcitonin gene-related peptide (CGRP) release from rat skin serves as an integrative measure of primary afferent activation by noxious heat and the presumed sensitising action of bradykinin and an activator of protein kinase C (PKC). The isolated rat hairy skin of either hind paw was mounted on acrylic rods and exposed for 5 min periods to synthetic interstitial fluid of either 32 degrees C for control or of higher temperatures up to 59 degrees C during stimulation. In addition, experiments were performed in calcium free solution (containing 10 mM EGTA) or the skin was preloaded with the membrane permeant calcium chelator BAPTA-AM (1 mM). To look for modulatory effects on the heat responses, bradykinin or polymyristate-acetate (PMA) were added during heat stimulation in further experiments. Heating the skin induced a temperature-dependent release of CGRP from a threshold of 43 degrees C which was absent in calcium free solution. Only at the highest temperatures (55 and 59 degrees C) was a partially calcium-independent release observed. Inhibition of the release was also obtained with the intracellular calcium buffer BAPTA-AM. Bradykinin 10 but not 1 microM as well as PMA 1 and 10 microM significantly facilitated the heat-induced CGRP release at 47 degrees C whereby BK caused a marginal and PMA a significant CGRP release by itself. Our results indicate that moderate noxious heat induces calcium-dependent CGRP release and this can be facilitated by bradykinin and by the activation of PKC. This suggests the same sensitising mechanism that affects nociceptor heat responses.

Animals↗
PubMed1996

Interaction of the protein import and folding machineries of the chloroplast.

We report the molecular cloning of import intermediate associated protein (IAP) 100, a 100-kDa protein of the chloroplast protein import machinery of peas. IAP100 contains two potential alpha-helical transmembrane segments and also behaves like an integral membrane protein. It was localized to the inner chloroplast envelope membrane. Immunoprecipitation experiments using monospecific anti-IAP100 antibodies and a nonionic detergent-generated chloroplast lysate gave the following results. (i) The four integral membrane proteins of the outer chloroplast import machinery were not coprecipitated with IAP100 indicating that the inner and outer membrane import machineries are not coupled in isolated chloroplasts. (ii) the major protein that coprecipitated with IAP100 was identified as stromal chaperonin 60 (cpn60); the association of IAP100 and cpn60 was specific and was abolished when immunoprecipitation was carried out in the presence of ATP. (iii) In a lysate from chloroplasts that had been preincubated for various lengths of time in an import reaction with radiolabeled precursor (pS) of the small subunit of Rubisco, we detected coimmunoprecipitation of IAP100, cpn60, and the imported mature form (S) of precursor. Relative to the time course of import, coprecipitation of S first increased and then decreased, consistent with a transient association of the newly imported S with the chaperonin bound to IAP100. These data suggest that IAP100 serves in recruiting chaperonin for folding of newly imported proteins.

Amino Acid Sequence↗
PubMed1994

Isolation of components of the chloroplast protein import machinery.

Components of the protein import machinery of the chloroplast were isolated by a procedure in which the import machinery was engaged in vitro with a tagged import substrate under conditions that yielded largely chloroplast envelope-bound import intermediates. Subsequent detergent solubilization of envelope membranes showed that six envelope polypeptides copurified specifically and, apparently, stoichiometrically with the import intermediates. Four of these polypeptides are components of the outer membrane import machinery and are associated with early import intermediates. Two of these polypeptides have been characterized. One is a homolog of the heat shock protein hsp70; the other one is a channel-protein candidate.

Adenosine Triphosphate↗
PubMed1994

Identification of two GTP-binding proteins in the chloroplast protein import machinery.

Two of four proteins that associated with translocation intermediates during protein import across the outer chloroplast envelope membrane were identified as guanosine triphosphate (GTP)-binding proteins. Both proteins are integral membrane proteins of the outer chloroplast membrane, and both are partially exposed on the chloroplast surface where they were accessible to thermolysin digestion. Engagement of the outer membrane's import machinery by an import substrate was inhibited by slowly hydrolyzable or non-hydrolyzable GTP analogs. Thus, these GTP-binding proteins may function in protein import into chloroplasts.

Adenosine Triphosphate↗
PubMed1992

Study of calmodulin binding to the alternatively spliced C-terminal domain of the plasma membrane Ca2+ pump.

The C-terminal regions of the four human plasma membrane Ca2+ pump isoforms 1a-d generated from alternatively spliced RNA have been expressed in Escherichia coli, and the recombinant proteins have been purified to a very high degree. The C-termini of isoforms 1a, 1c, and 1d contain an insert encoded by an alternatively spliced exon which is homologous to the calmodulin binding domain of isoform 1b. In isoforms 1c and 1d (29 and 38 amino acid insertions, respectively), subdomain A of the original calmodulin binding site of isoform 1b is followed by the spliced-in domain, which is then followed by subdomain B of the original calmodulin binding site. The positive charges of histidine residues at positions 27, 28, and 38 of the alternatively spliced sequence are likely to be responsible for the observed pH-dependent calmodulin binding to the novel "duplicated" binding site. The affinity of calmodulin for the C-terminal domains of isoforms 1a, 1c, and 1d, which contain the histidine-rich inserts, is much higher at pH 5.9 than at pH 7.2. A synthetic peptide (I31) containing 31 amino acids of the alternatively spliced sequence (from residue 9 to 40) also binds calmodulin with strong pH dependency. Alternative splicing in the C-terminal domain is proposed to confer pH dependence to the regulation of the activity of Ca2+ pump isoforms.

Amino Acid Sequence↗
PubMed1990

Partial purification and characterization of the Ca2(+)-pumping ATPase of the liver plasma membrane.

A Ca2(+)-pumping ATPase has been characterized in rat hepatocyte plasma membranes. The enzyme has high Ca2+ affinity, and properties typical of a P-type ion pump. At variance with the Ca2+ pumps of other eukaryotic plasma membranes, it is not stimulated by calmodulin. The steady state concentration of the phosphoenzyme formed in the presence of ATP is increased by La3+. The enzyme cross-reacts with a monoclonal antibody (mAb-5F10) raised against the human erythrocyte Ca2+ pump. The enzyme has been purified using a mAb-5F10 antibody affinity column. CNBr digestion of the isolated protein has yielded two peptides which have been sequenced. One of them matches perfectly a sequence contained in the erythrocyte Ca2+ pump, the other is very homologous to another domain in the erythrocyte pump. In spite of the absence of calmodulin stimulation, 125I-calmodulin overlay experiments on the purified liver ATPase under denaturing conditions have revealed that the enzyme binds calmodulin even more strongly than the erythrocyte pump. Immunocytochemical experiments on liver slices using the mAb-5F10 antibody have shown that the enzyme is located predominantly in the blood sinusoidal domain of the hepatocyte plasma membrane.

Amino Acid Sequence↗
PubMed1983

Endoscopic Nd:YAG laser therapy for carcinoma of the esophagus: a new form of palliative treatment.

A new palliative treatment technique for esophageal carcinoma using endoscopic neodymium:yttrium aluminum garnet (Nd:YAG) laser therapy is described in 14 patients for whom no curative therapy is possible. Tumors ranged in length from 5 to 11 cm (mean 8.2 cm) and in 11 patients luminal occlusion before treatment was greater than 90%. The mean number of treatments required to alleviate symptoms and remove obstruction was 5.3 (range 2-13) and the mean number of days required was 11.6 (range 5-28). An average of 4615 W-s were given per treatment and the mean total energy per patient was 24,394 W-s. In all 14 patients, clinical, endoscopic, and radiographic improvement was noted. Two major complications occurred which may possibly have been caused by laser therapy. The overall results are encouraging and hold promise for a patient population in whom the therapeutic options are generally very limited.

Aged↗