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Biomedical subjects

G Schreiber

Publications and source records attributed to G Schreiber.

At least 73 records · Page 4Linked to original sources
PubMed1998

Evolution of thyroid hormone distribution.

1. Appropriate distribution of thyroxine between the lipid-soluble compartments of cells and tissues and the extracellular aqueous space is established by binding to extracellular proteins. Among these proteins, transthyretin is of particular interest because it is the only one synthesized in the brain. 2. The evolutionary onset of transthyretin synthesis in cells of the blood-brain barrier precedes that in the liver, with the exception of a very short period of transthyretin synthesis in the liver of tadpoles, just prior to the climax of metamorphosis. In adult liver, transthyretin is only synthesized in endothermic vertebrates. 3. The affinity of transthyretin for thyroxine increases and that for 3,5,3'-triiodothyronine decreases during the evolution of eutherians from reptile/bird-like common ancestors. 4. A systematic change of the N-terminal region of transthyretin occurred during evolution, leading to shorter and more hydrophilic transthyretin N termini in eutherians compared with those in reptiles and birds. 5. The molecular mechanism of the evolution of the transthyretin N termini is a stepwise shift of the splice site at the intron 1/exon 2 border in the 3' direction. The most probable cause for this shift is a series of single base mutations. 6. As the N termini are located on the surface of transthyretin near the entrance to its central channel leading to the thyroxine binding sites, it is possible that a change in the structure of this region could influence the access of thyroxine to the binding sites. The increase in affinity for thyroxine could then be a driving force in the natural selection during evolution of transthyretins with shorter and more hydrophilic N termini.

Amino Acid Sequence↗
PubMed1998

Dynamics of ECT normalization of low G protein function and immunoreactivity in mononuclear leukocytes of patients with major depression.

OBJECTIVE: Heterotrimeric G proteins were previously implicated in the biochemical mechanisms underlying the pathophysiology and treatment of mood disorders. Low function and immunoreactivity of G proteins were observed in patients with major depression. In the present study the authors evaluated the effects of ECT on the low measures of G proteins in patients with major depression. METHOD: Repeated G protein measurements in mononuclear leukocytes of 10 patients with major depression were made. Each patient was examined while untreated and after successive sessions of ECT; 14 normal subjects were also studied. G protein function was evaluated through beta-adrenergic- and muscarinic-agonist-enhanced guanine nucleotide binding capacity, substantiated by quantitative measures of G proteins through immunoblot analyses using polyclonal antibodies against Gs alpha, Gi alpha, and G beta proteins. RESULTS: Mononuclear leukocytes of patients with depression showed immunoreactive levels of Gs alpha and Gi alpha that were significantly lower than those of normal subjects; the depressed patients also had markedly hypofunctional Gs and Gi. The low levels of G protein function and immunoreactivity were alleviated by ECT. Repeated measurements in the same patients after successive ECT sessions showed that the normalization of G protein measures preceded, and thus predicted, clinical improvement. The function and quantity of Gs and Gi proteins in patients given ECT were significantly correlated. CONCLUSIONS: These findings support the implication of G proteins in the pathophysiology and treatment of mood disorders. G protein measurements in patients with depression may potentially serve not only as a biochemical marker for affective state but also for biochemical prediction and evaluation of responses to ECT.

Biomarkers↗
PubMed1997

Synthesis and evaluation of (S)-4-(3-(2'-[11C]isopropylamino)-2-hydroxypropoxy) -2H-benzimidazol -2-one ((S)-[11C]CGP 12388) and (S)-4-(3-((1'-[18F]-fluoroisopropyl)amino)-2-hydroxypropoxy) -2H- benzimidazol-2-one ((S)-[18F]fluoro-CGP 12388) for visualization of beta-adrenoceptors with positron emission tomography.

The beta-adrenoceptor antagonist (S)-[11C]CGP 12177 (4-(3-(tert-butylamino)-2-hydroxypropoxy)-2H-benzimidazol -2[11C]- one) is a generally accepted radioligand for cardiac and pulmonary PET studies. The synthesis of [11C]CGP 12177 is a laborious and often troublesome procedure. Therefore, (S)-CGP 12388 (4-(3-(isopropylamino)-2-hydroxypropoxy) -2H-benzimidazol-2-one), 5, the isopropyl analogue of CGP 12177, has been labeled with carbon-11 in the isopropyl group via a reductive alkylation by [11C]acetone (3) of the corresponding (S)-desisopropyl compound 2. The fluoro-substituted analogue of (S)-CGP 12388 was prepared by reacting 2 with [18F]fluoroacetone (4). (S)-[11C]CGP 12388 (5) was easily prepared via a one-pot procedure. The radiochemical yield of (S)-[11C]CGP 12388 (600-800 Ci/mmol, EOS) was 18% (EOB) with a total synthesis time of 35 min, whereas (S)-[18F]fluoro-CGP 12388 (6) (> 2000 Ci/mmol, EOS) was synthesized in 105 min with a radiochemical yield of 12% (EOB). Biodistribution studies in rats demonstrated specific binding to beta-adrenoceptors of (S)-[18F]fluoro-CGP 12388 and (S)-[11C]CGP 12388 in lung and heart. The lungs were clearly visualized with PET studies of rats. Total/nonspecific binding at 60 min postinjection was 5.6 for (S)-[11C]CGP 12388 and 2.0 for the (S)-18F compound. Due to its facile synthetic procedure and in vivo data, (S)-[11C]CGP 12388 is a promising beta-adrenoceptor ligand for clinical PET.

Adrenergic beta-Antagonists↗
PubMed1997

The role of Glu73 of barnase in catalysis and the binding of barstar.

Barnase, a small extracellular ribonuclease from Bacillus amyloliquefaciens and its intracellular inhibitor barstar have co-evolved to bind tightly and rapidly. Barnase has also evolved to be catalytically active. The active site of barnase and its binding site for barstar use the same subset of amino acids. The exception is Glu73 (the general base in catalysis), which although located at the centre of the binding site, is separated by three ordered water molecules from barstar. We examined in this work the contribution of Glu73 to both catalysis and barstar binding. Truncation mutants of the general base (Glu73 --> Ala or Ser) retain a residual RNase activity of about 0.3% while mutants with larger hydrophobic replacements (Glu 73 --> Trp or Phe) have virtually no catalytic activity. This, and binding data of 3'-GMP with the different barnase mutants suggest that the loss in activity results from the elimination of the general base, which can be substituted to some extent by water or other polar side-chains in truncation mutants. All of the Glu73 mutations lead to a weakening of the free energy of complex formation with barstar by 1.4 to 3.0 kcal/mol (including Gln). This is surprising, since Glu73 does not interact directly with barstar and there is an electrostatic repulsion between Glu73 on barnase and the negatively charged binding surface of barstar. A newly developed method of constructing double mutant cycles between multiple mutations at the same site appears to pinpoint a favourable interaction between Glu73 and one of its nearest neighbours in barstar, Asp39. The coupling energy between those residues is presumably indirect: the carboxylate of Glu73 organizes neighbouring positively charged groups in barnase, Lys27, Arg83, and Arg87 to interact with Asp39 in barstar. This emphasizes that an apparent interaction between a pair of residues as measured with double mutant cycles is the sum of their direct and indirect interactions.

Bacterial Proteins↗
PubMed1997

Evolution of shorter and more hydrophilic transthyretin N-termini by stepwise conversion of exon 2 into intron 1 sequences (shifting the 3' splice site of intron 1)

Transthyretin cDNA was cloned from Eastern Grey Kangaroo liver and its nucleotide sequence determined. Analysis of the derived amino acid sequence of kangaroo transthyretin, together with data obtained previously for transthyretins from other vertebrate species [Duan, W., Richardson, S. J., Babon, J. J., Heyes, R. J., Southwell, B. R., Harms, P. J., Wettenhall, R. E. H., Dziegielewska, K. M., Selwood, L., Bradley, A. J., Brack, C. M. & Schreiber, G. (1995) Eur. J. Biochem. 227, 396-406], showed that the N-terminus is the region which changes most distinctly during evolution. It has been shown for human, mouse and rat transthyretins, that this region is encoded by DNA at the border of exon 1 and exon 2. Therefore, this section of transthyretin genomic DNA was amplified by PCR and directly sequenced for the Buffalo Rat, Tammar Wallaby, Eastern Grey Kangaroo, Stripe-faced Dunnart, Short-tailed Grey Opossum and White Leghorn Chicken. The splice sites at both ends of intron 1 were identified by comparison with the cDNA sequences. The obtained data suggest that the N-termini of transthyretin evolved by successive shifts of the 3' splice site of intron 1 in the 3' direction, resulting in successive shortening of the 5' end of exon 2. At the protein level, this resulted in a shorter and more hydrophilic N-terminal region of transthyretin. Successive shifts in splice sites may be an evolutionary mechanism of general importance, since they can lead to stepwise changes in the properties of proteins. This could be a molecular mechanism for positive Darwinian selection.

Amino Acid Sequence↗
PubMed1997

Fluorescence properties of a tryptophan residue in an aromatic core of the protein subunit of ribonuclease P from Escherichia coli.

Escherichia coli ribonuclease P (RNase P), a ribonucleoprotein complex which primarily functions in tRNA biosynthesis, is composed of a catalytic RNA subunit, M1 RNA, and a protein cofactor, C5 protein. The fluorescence emission spectrum of the single tryptophan residue-containing C5 protein exhibits maxima at 318 nm and 332 nm. Based on a comparison of the emission spectra of wild-type C5 protein and some of its mutant derivatives, we have determined that the 318 nm maximum could be the result of a complex formed in the excited state as a result of hydrophobic interactions between Trp109, Phe18 and Phe73. The analogous tryptophan fluorescence emission spectra of wild-type C5 protein and the barstar mutant W38F/W44F, taken together with the detailed structural information available for barstar, provide a possible explanation for the unusual emission spectrum of C5 protein.

Bacterial Proteins↗
PubMed1997

Thermodynamics of the interaction of barnase and barstar: changes in free energy versus changes in enthalpy on mutation.

We have studied the thermodynamics of the interaction between the ribonuclease barnase and its natural polypeptide inhibitor barstar. The contribution of specific residues and interactions within the barnase-barstar interface to the enthalpy of binding has been examined using isothermal titration calorimetry and protein engineering. The enthalpy of association of the wild-type proteins is -18.9 (+/-0.1) kcal/mol at pH 8 and at 25 degrees C. The enthalpy of binding remains favourable for 31 different combinations of mutations in the interface. The effects on the binding enthalpy upon replacing a side-chain involved in the interaction of barnase and barstar are, however, always unfavourable and in most cases larger than the effects on the free energy of binding. Interaction enthalpies calculated by double mutant cycle analysis are in some cases much larger than the interaction free energies. The interaction enthalpies for complexes between different barnase mutants with amino acid substitutions of the general base residue glutamic acid 73 and a barstar variant (D39A) vary by as much as 8.3 kcal/mol while the coupling free energies differ only by 1 kcal/mol. The use of enthalpies for the analysis of structure-activity relationships appears to be complicated by enthalpy-entropy compensation of weak intermolecular interactions. These tend to cancel out in measurements of free energy, which is thus the preferred quantity for simple analysis of interactions.

Bacillus↗
PubMed1997

The folding pathway of a protein at high resolution from microseconds to seconds.

We have documented the folding pathway of the 10-kDa protein barstar from the first few microseconds at the resolution of individual residues from its well characterized denatured state. The denatured state had been shown from NMR to have flickering native-like structure in the first two of its four alpha-helices. phi-value analysis shows that the first helix becomes substantially consolidated as the intermediate is formed in a few hundred microseconds, as does the second to a lesser extent. A native-like structure then is formed in a few hundred milliseconds as the whole structure consolidates. Peptide fragments corresponding to sequences containing the first two helices separately and together as a helix-loop-helix motif have little helical structure under conditions that favor folding. The early stages of folding fit the nucleation-condensation model that was proposed for the smaller chymotrypsin inhibitor 2, which is a single module of structure and folds by two-state kinetics. The early stages of the multistate folding of the larger, multimodular, barnase have proved experimentally inaccessible. The folding pathway of barstar links those of CI2 and barnase to give a unified scheme for folding.

Bacterial Proteins↗
PubMed1997

Reduced Gs protein function and G alpha s levels in leukocytes of patients with Parkinson's disease.

Early events in signal information transduction beyond dopamine, beta-adrenergic, and muscarinic receptors, involving receptor-coupled G-protein function and G alpha subunit immunoreactive levels were measured in mononuclear leukocytes (MNLs) of 12 never-treated patients with Parkinson's disease in comparison with 10 age- and sex-matched healthy control subjects. Both beta-adrenergic and dopamine receptor-coupled Gs protein function as measured by cholera toxin-sensitive, isoproterenol- and dopamine-induced increases in Gpp(NH)p-binding capacity, in MNLs of patients with Parkinson's disease were found to be significantly reduced in comparison with those in the control group. Muscarinic receptor-coupled non-Gs (Gi or G(o)) protein function: pertussis toxin-sensitive, carbamylcholine-induced increase in Gpp(NH)p-binding capacity, was not found to be significantly different between patients with Parkinson's disease and control subjects. G protein alpha subunits were measured through immunoblotting analyses with specific polyclonal antibodies against G alpha s, G alpha i, and G alpha q subunits. MNL levels of the 45-kDa species of G alpha s were found to be significantly reduced in patients with Parkinson's disease in comparison with control subjects. Other non-Gs proteins (Gi, Gq) did not show any significant quantitative differences between patients with Parkinson's disease and control subjects. The reductions in G alpha s levels in MNLs of patients with Parkinson's disease may explain the beta-adrenergic and dopamine receptor-coupled Gs protein hypofunction detected in MNLs of these patients. As previous studies have failed to observe significant changes in receptor levels in MNLs of patients with Parkinson's disease, our findings of reduced dopaminergic and beta-adrenergic receptor-coupled Gs function and of G alpha s immunoreactive levels in MNLs of Parkinson's patients point to alterations distal to these receptors at the level of the signal-transducing Gs protein.

Adult↗
PubMed1997

[Pseudoxanthoma elasticum. Skin changes as a marker of systemic illness].

Angioid streaks were diagnosed in a 42-year-old woman. Since age 20 she had developed circumscribed atrophic yellow-grey lesions on her neck, axillae and other flexural sites. In spite of highly characteristic skin changes, the diagnosis of pseudoxanthoma elasticum was first confirmed by a biopsy from lesional skin 22 years after the disease onset. Based on the present case and an analysis of the recent literature, the findings characteristic for pseudoxanthoma elasticum in the skin, eyes and cardiovascular system are delineated, the differential diagnosis of the skin lesions, as well as the pathogenesis and the prognosis are discussed, and the new classification of pseudoxanthoma elasticum, based on major and minor criteria, is described.

Adult↗
PubMed1997

Differential G protein measures in mononuclear leukocytes of patients with bipolar mood disorder are state dependent.

Quantitative and functional measurements of G proteins were undertaken in mononuclear leukocytes of bipolar disordered patients comparing bipolar depressed with manic patients groups in order to verify whether any alterations observed in G protein functional or immunoreactive measures in bipolar mood disorder are state- or trait-dependent characteristics. Compared with the control group of 30 subjects, isoproterenol- and carbamylcholine-enhanced Gpp(NH)p binding capacities were highly significantly increased in the group of 20 manic patients, while highly significantly reduced in the group of 11 bipolar depressed patients. While manic patients showed highly significant elevations in mononuclear leukocytes levels of G alpha s and G alpha i, evaluated through immunoblot analysis using specific polyclonal antibodies against the subunit proteins, mononuclear leukocytes of bipolar depressed patients show significant reductions in G alpha s and G alpha i immunoreactive levels. G beta subunit levels were found to be similar in all three groups. The changes in G protein measures observed in mononuclear leukocytes of mood disordered patients thus represent state characteristics of the disorder.

Adult↗
PubMed1997

The evolution of gene expression, structure and function of transthyretin.

Thyroxine, the most abundant thyroid hormone in blood, partitions into lipid membranes. In a network-like system, thyroxine-binding plasma proteins counteract this partitioning and establish intravascular, protein-bound thyroxine pools. These are far larger than the free thyroxine pools. In larger eutherians, proteins specifically binding thyroxine are albumin, transthyretin, and thyroxine-binding globulin. Some binding of thyroxine can also occur to lipoproteins. During evolution, transthyretin synthesis first appeared in the choroid plexus of the stem reptiles, about 300 million years ago. Transthretin synthesis in the liver evolved much later, independently, in birds, eutherians and some marsupial species. Analysis of 57 human transthyretin variants suggests that most mutations in transthyretin are not compatible with its normal metabolism and lead to its deposition as amyloid. Analysis of transthyretin or its gene in 20 different species shows that evolutionary changes of transthyretin predominantly occurred near the N-termini. A change in RNA splicing between exon 1 and exon 2 led to a decrease in hydrophobicity and length of the N-termini. It is proposed that the selection pressure producing these changes was the need for a more effective prevention of thyroxine partitioning into lipids. Lipid pools increased during evolution with the increases in relative sizes of brains and internal organs and changes in lipid composition of membranes in ectothermic and endothermic species.

Amino Acid Sequence↗
PubMed1997

Abundant synthesis of transthyretin in the brain, but not in the liver, of turtles.

The binding of thyroxine to proteins in the blood plasma of the turtle, Trachemys scripta, was analyzed by incubation with radioactive thyroxine, electrophoresis and autoradiography. Albumin and an alpha-globulin were found to bind thyroxine; no thyroxine-binding transthyretin was detected in the prealbumin region. In contrast to blood plasma, a thyroxine-binding prealbumin was observed in medium from T. scripta choroid plexus incubated in vitro. RNA was extracted from brain tissue containing choroid plexus and from liver of T. scripta and Chelydra serpentina and analyzed by hybridization with transthyretin cDNA from the lizard Tiliqua rugosa. The brain RNAs contained substantial amounts of transthyretin mRNA, whereas only trace amounts of transthyretin mRNA were detected in RNA from liver. No transthyretin mRNA was observed in RNA from kidney. The results support the hypothesis that the expression of the transthyretin gene first evolved in the choroid plexus of the brain at the stage of the stem reptiles, whereas abundant transthyretin synthesis in liver evolved much later, and independently, in mammals and birds.

Animals↗
PubMed1997

Photoperiodicity and annual rhythms of wars and violent crimes.

The seasonal variations of individual violent crimes, i.e. sexual offenses and aggravated assaults, and non-violent offenses, i.e. burglary, in Israel, the USA, Denmark and New South Wales, Australia, representing four continents, were analyzed. Seasonal variations in the opening dates of wars were similarly analyzed. In northern hemisphere countries, although non-violent offenses are distributed equally throughout the year, individual violent crimes and collective acts of hostility are characterized by an annual rhythm of incidence, with a peak in the months of July-August and a nadir in December-February. Inverse rhythms were obtained in southern hemisphere countries. These rhythms were found to be correlated in a statistically significant manner with the duration of the daily photoperiod. The existence of similar patterns of annual variations in violent crimes and in the opening dates of wars indicate similarities between individual and collective aggressiveness with respect to the underlying mechanisms and probably also to the means of their prevention.

Aggression↗
PubMed1997

Measurement of serum exon 3-retaining growth hormone-binding protein in children and adolescents by radioimmunoassay.

Recently described assays for the determination of growth hormone-binding protein (GHBP) show a wide variety of normal ranges. Their results depend on the assay design and in the case of ligand-immunofunctional assay (LIFA), probably also on the binding characteristics, i.e. epitope specificity and affinity of the employed antibody. These facts underline the necessity to look for more accurate and specific assays. In this report we describe an accurate and simple radioimmunoassay (RIA) which allows the specific quantitation of the exon 3-retaining GHBP isoform (E3-GHBP). Data of the E3-GHBP RIA were compared to those of a LIFA measuring undifferentiated functional forms of GHBP. Our results demonstrate significant relationships between GHBP and age, BMI and IGF-I as determined by RIA and by LIFA in normal children and adolescents (n = 115, p < 0.001). Moreover, BMI is the only regulating factor of GHBP for both methods as shown by multiple regression analysis (p < 0.001). All our data suggest a qualitatively paralleled regulation of E3-GHBP and undifferentiated functional GHBP forms. This finding was confirmed by a good correlation between RIA and LIFA data (r = 0.74, p < 0.001). Children with idiopathic short stature (ISS, n = 47) had significantly lower GHBP levels than normal controls (n = 58) measured by the E3-GHBP RIA (p < 0.0001) and by LIFA (p < 0.01). We conclude that (1) ISS children may have a structural or quantitative defect at the level of the GHR, and (2) the highly specific assay for E3-GHBP immunoreactivity provides a sensitive diagnostic tool in conditions with partial GH insensitivity.

Adolescent↗
PubMed1997

Reduced G protein functions and immunoreactive levels in mononuclear leukocytes of patients with depression.

OBJECTIVE: Heterotrimeric G proteins play a pivotal role in postreceptor information transduction. These proteins were previously implicated in the biochemical mechanism underlying lithium action and in the pathophysiology of mood disorders. The present study sought to quantitatively and functionally evaluate G proteins in patients with major depression. METHOD: G proteins were measured in mononuclear leukocytes of 37 untreated patients with major depression and 31 comparison subjects. Receptor-coupled G protein function was evaluated through beta-adrenergic and muscarinic-agonist-induced increases in guanine nucleotide binding capacity, which were substantiated by quantitative measures of G proteins through immunoblot analyses that used polyclonal antibodies against stimulatory (Gs alpha) and inhibitory (Gi alpha) G proteins. RESULTS: Mononuclear leukocytes of depressed patients showed significantly reduced immunoreactive quantities of Gs alpha and Gi alpha together with markedly hypofunctional Gs and Gi. The reductions in both function and quantity of Gs and Gi were significantly correlated with the severity of depressive symptoms. Moreover, simultaneous quantitative and functional measurements in a large number of patients showed significant correlations between the function and the quantity of mononuclear leukocyte Gs and Gi proteins: CONCLUSIONS: These findings lend further support to the implication of G proteins in the pathophysiology of mood disorders. G protein functional and quantitative measurements in mononuclear leukocytes of patients with mood disorders may potentially serve as a biochemical marker for the affective state of these patients.

Adult↗
PubMed1997

Smoking, gender, and survival association with allele loss for the LOH11B lung cancer region on chromosome 11.

We have reported frequent allele loss for the marker HRAS on chromosome 11p in human lung cancer and defined the smallest common region of deletion (designated LOH11B) to approximately 500 kb. Here, we investigated the association of allele loss for LOH11B with epidemiological, pathological, and clinical parameters. Analysis of allele loss was performed using Southern blotting on a cohort of 200 patients with lung cancer, and data were interpreted with the use of a phosphorimager. Results were statistically compared with retrospectively collected variables. LOH11B allele loss was significantly associated with cigarette consumption (P = 0.009), gender (P = 0.02), and survival (P = 0.04). None of the nonsmokers had allele loss as compared with 28% of the patients with low and 43% with high cigarette consumption. Allele loss was more frequent in men (43%) than in women (11%). The median survival of patients without allele loss was 42 months compared with 25 months for patients with allele loss. These results suggest that the LOH11B region contains a gene responsible for a more malignant phenotype independent of the metastatic potential of lung cancer. They also suggest that alterations in this gene are associated with cigarette consumption and are more frequent in men than in women.

Adult↗