Biomedical subjects

R Seidel

Publications and source records attributed to R Seidel.

At least 19 recordsLinked to original sources

PubMed2001

The chaperone function of ClpB from Thermus thermophilus depends on allosteric interactions of its two ATP-binding sites.

ClpB belongs to the Hsp100 family and assists de-aggregation of protein aggregates by DnaK chaperone systems. It contains two Walker consensus sequences (or P-Loops) that indicate potential nucleotide binding domains (NBD). Both domains appear to be essential for chaperoning function, since mutation of the conserved lysine residue of the GX(4)GKT consensus sequences to glutamine (K204Q and K601Q) abolishes its properties to accelerate renaturation of aggregated firefly luciferase. The underlying biochemical reason for this malfunction appears not to be a dramatically reduced ATPase activity of either P-loop per se but rather changed properties of co-operativity of ATPase activity connected to oligomerization properties to form productive oligomers. This view is corroborated by data that show that structural stability (as judged by CD spectroscopy) or ATPase activity at single turnover conditions (at low ATP concentrations) are not significantly affected by these mutations. In addition nucleotide binding properties of wild-type protein and mutants (as judged by binding studies with fluorescent nucleotide analogues and competitive displacement titrations) do not differ dramatically. However, the general pattern of formation of stable, defined oligomers formed as a function of salt concentration and nucleotides and more importantly, cooperativity of ATPase activity at high ATP concentrations is dramatically changed with the two P-loop mutants described.

Adenosine Diphosphate↗

PubMed2001

Regulation of ATPase and chaperone cycle of DnaK from Thermus thermophilus by the nucleotide exchange factor GrpE.

The nucleotide binding and release cycle of the molecular chaperone DnaK is regulated by the accessory proteins GrpE and DnaJ, also called co-chaperones. The concerted action of the nucleotide exchange factor GrpE and the ATPase-stimulating factor DnaJ determines the ratio of the two nucleotide states of DnaK, which differ in their mode of interaction with unfolded proteins. In the Escherichia coli system, the stimulation by these two antagonists is comparable in magnitude, resulting in a balance of the two nucleotide states of DnaK(Eco) in the absence and the presence of co-chaperones. The regulation of the DnaK chaperone system from Thermus thermophilus is apparently substantially different. Here, DnaJ does not stimulate the DnaK-mediated ATP hydrolysis and thus does not appear to act as an antagonist of the nucleotide exchange factor GrpE(Tth). This raises the question of whether T. thermophilus GrpE stimulates nucleotide exchange to a smaller degree as compared to the E. coli system and how the corresponding rates relate to intrinsic ATPase and ATP binding as well as luciferase refolding kinetics of T. thermophilus DnaK. We determined dissociation constants as well as kinetic constants that describe the interactions between the T. thermophilus molecular chaperone DnaK, its nucleotide exchange factor GrpE and the fluorescent ADP analogue N8-(4-N'-methylanthraniloylaminobutyl)-8-aminoadenosine-5'-diphosphate by isothermal equilibrium titration calorimetry and stopped-flow kinetic experiments and investigated the influence of T. thermophilus DnaJ on the DnaK nucleotide cycle. The interaction of GrpE with the DnaK.ADP complex versus nucleotide-free DnaK can be described by a simple equilibrium system, where GrpE reduces the affinity of DnaK for ADP by a factor of about 10. Kinetic experiments indicate that the maximal acceleration of nucleotide release by GrpE is 80,000-fold at a saturating GrpE concentration. Our experiments show that in T. thermophilus, although the thermophilic DnaK system displays no stimulation of the DnaK-ATPase activity by DnaJ, nucleotide exchange is still efficiently stimulated by GrpE. This indicates that two counteracting factors are not absolutely necessary to maintain a functional and regulated chaperone cycle. This conclusion is corroborated by data that show that the slower ATPase cycle of the DnaK system as well as of heterologous T. thermophilus DnaK/E. coli DnaK systems is directly reflected in altered refolding kinetics of firefly luciferase but not necessarily in refolding yields.

Adenosine Diphosphate↗

PubMed2001

Lymphangioma of the pancreas and the duodenal wall: MR imaging findings.

Pancreatic lymphangiomas are rare benign tumours with a histogenesis not yet completely understood. Predominantly the cystic aspect of this lesion can complicate the differentiation from other neoplastic and non-neoplastic cystic tumours of the pancreas. We present a case of a middle-aged woman with a lymphangioma involving the duodenal wall and the pancreatic head. With special regard to MR imaging findings differential diagnosis is discussed.

Adult↗

PubMed2000

A transcultural outcome study of adolescent eating disorders.

OBJECTIVE: The aim of the study was to assess the treatment and outcome of adolescent eating disorders in an international study including Western and Eastern European clinical and research centres. METHOD: A total of 138 patients with adolescent onset of an eating disorder (primarily anorexia nervosa) were followed-up after a mean interval of 5 years after first admission. RESULTS: On average, the patients had spent 25% of the total follow-up period in either in-patient or out-patient treatment. Half of them required a second hospitalization and a quarter required a third hospitalization for the eating disorder. At follow-up, 68% of the total sample did not have an eating disorder. The prediction of outcome revealed different patterns of risk variables depending on the type of criterion. CONCLUSION: The outcome of adolescent eating disorders is relatively similar across cultures, and better than in patients with later onset of the disorder.

Adolescent↗

PubMed2000

In vivo microscopic evaluation of the microvascular behavior of FITC-labeled macromolecular MR contrast agents in the hamster skinfold chamber.

RATIONALE AND OBJECTIVES: The extravasation properties of two macromolecular MR imaging contrast media (CM) in relation to structural differences of the terminal vascular bed were investigated to determine whether differentiation between normal (physiological) and tumor (pathological) tissue can be achieved by means of extravasation characteristics. METHODS: Gd-DTPA-polylysine (50 kD, CM1) and Gd-DOTA cascade polymer (Gadomer 17; 20 kD, CM2) were labeled with fluorescein isothiocyanate (FITC) to enable in vivo fluorescence microscopy of the microcirculation. After implantation of a dorsal skinfold chamber and 7 days (range, 6-8) after induction of an amelanotic melanoma (A-Mel-3), 14 male hamsters weighing 85 g (range, 70-95 g) received 200 micromol/kg of CM1 by intravenous injection into the jugular vein. CM2 was similarly investigated after an interval of 24 hours. Fluorescence microscopy was performed in areas of subcutaneous tissue, striated muscle, and tumor tissue. Microscopic images were registered by a charge-coupled-device video camera and transferred to a video system. Distribution intensities of CM were evaluated on a digitally based measurement system. A control investigation was performed with FITC-dextran (150 kD). RESULTS: Gd-DTPA-polylysine showed no extravasation into physiological tissue for the first 10 minutes after injection. After this period, however, the first signs of leakage became apparent. Gd-DOTA cascade polymer was extravasated after 5 minutes into the tumor-free tissue. In tumor capillaries, Gd-DTPA-polylysine could be detected in the extravasal space as well as in physiological tissue after 15 minutes. After injection of Gd-DOTA cascade polymer, direct leakage from tumor capillaries was observed, with a contrast maximum between tumor and surrounding tissue occurring 3 to 5 minutes after CM injection. Good delineation of tumor vascularization from striated muscle and subcutaneous tissue was achieved. CONCLUSIONS: The CM studied showed different microvascular permeation properties. Faster leakage of Gd-DOTA cascade polymer was observed in areas with neoplastic tumor vessels, whereas extravasation in physiological tissue was detected after a period of 5 minutes. Gd-DTPA-polylysine demonstrated nonspecific leakage at later time points.

Animals↗

PubMed1999

The functional cycle and regulation of the Thermus thermophilus DnaK chaperone system.

The Escherichia coli DnaK (DnaKEco) chaperone cycle is tightly regulated by the cochaperones DnaJ, which stimulates ATP hydrolysis, and GrpE, which acts as a nucleotide exchange factor. The Thermus thermophilus DnaK (DnaKTth) system additionally comprises the DnaK-DnaJ assembly factor (DafATth) that is mediating formation of a 300 kDa DnaKTth. DnaJTth.DafATth complex.A model peptide derived from the tumor suppressor protein p53 was used to dissect the regulation of the individual kinetic key steps of the DnaKTth nucleotide/chaperone cycle. As with DnaKEco the DnaKTth.ATP complex binds substrates with reduced affinity and large exchange rates compared to the DnaKTth.ADP.Pi state. In contrast to DnaKEco, ADP-Pi release is slow compared to the rate of hydrolysis, reversing the balance of the two functional nucleotide states. Whereas GrpETth stimulates nucleotide release from DnaKTth, DnaJTth does not accelerate ATP hydrolysis under various experimental conditions. However, it exerts influence on the interaction of DnaKTth with substrates: in the presence of DafATth, DnaJTth inhibits substrate binding, and substrate already bound to DnaKTth is displaced by DnaJTth and DafATth, indicating competitive binding of DnaJTth/DafATth and substrate. It thus appears that the DnaKTth. DnaJTth.DafATth complex as isolated from T. thermophilus does not represent the active species in the DnaKTth chaperone cycle. Isothermal titration calorimetry showed that the ternary complex of DnaKTth, DnaJTth and DafATth is assembling with high affinity, whereas binary complexes of DnaKTth and DnaJTth or DafATth were not detectable, indicating highly synergistic formation of the 300 kDa DnaKTth. DnaJTth.DafATth complex. Based on these results, a model describing the DnaKTth chaperone cycle and its regulation by cochaperones is proposed where DnaKTth. DnaJTth.DafATth constitutes the resting state, and a DnaKTth. substrate.DnaJTth complex is the active chaperone species. The novel factor DafATth that mediates interaction of DnaKTth with DnaJTth would thus serve as a "template" to stabilise the ternary DnaKTth.DafATth.DnaJTth complex until it is replaced by substrate proteins under heat shock conditions.

Adenosine Triphosphate↗

PubMed1999

Endoscopic removal of an esophageal fibrovascular polyp.

Fibrovascular polyps are intraluminal pedunculated esophageal polyps, which can produce devastating consequences if untreated. Therapy for these lesions is traditionally surgical, with esophagotomy. The present report describes a case of endoscopic removal of a fibrovascular polyp, alleviating the need for hospitalization or further interventions. The natural history, clinical presentation, diagnostic evaluation, and therapies are reviewed.

Electrocoagulation↗

PubMed1998

Functional properties of the molecular chaperone DnaK from Thermus thermophilus.

The genes coding for the Thermus thermophilus (Tth) homologues of the molecular chaperones DnaK and GrpE (DnaKTth and GrpETth) were cloned and expressed in Escherichia coli. The proteins were purified and their functional properties were assessed by equilibrium and transient kinetic methods. DnaKTth has an intrinsic ATPase activity of 3x10(-4) s-1 at 25 degreesC and 10x10(-4) s-1 at 75 degreesC under single turnover conditions. It binds the fluorescent nucleotide analogue N8-(4-N'-methylanthraniloylaminobutyl)-8-aminoadenosine 5'-diphosphate (MABA-ADP) with a dissociation constant (Kd) of 3 nM and ADP with a Kd of 47 nM at 25 degreesC. At 75 degreesC the affinities are decreased fivefold to 15 nM (MABA-ADP) and 280 nM (ADP). The kinetic constants for two-step binding of MABA-ADP and of ADP to DnaKTth were determined at 25 degreesC and 75 degreesC, respectively. GrpETth acts as a nucleotide-exchange factor on DnaKTth and accelerates the release of bound MABA-ADP significantly. This shows that the nucleotide-binding domain is functionally intact, and that the specific interaction of DnaKTth and GrpETth is mediating nucleotide exchange.A fluorescently labelled peptide that comprises a subsequence of the E. coli transcription factor sigma32 binds to nucleotide-free DnaKTth with a Kd of 4.9 microM. Displacement with unlabelled peptide yields a Kd of 5.0 microM for the unlabelled peptide. Thus the peptide-binding domain also appears to be functional.For the cellular chaperone function of DnaK, a coupling between nucleotide and peptide-binding domains is required. However, with DnaKTth in the ATP as well as in the ADP.Pi-state, peptide is bound and released within seconds. No correlation between ATP-binding or hydrolysis by DnaKTth and changes in the sigma32 peptide exchange rates could be detected. It thus appears that the DnaK system from Th. thermophilus has a different mechanism of coupling the nucleotide state to the fast and slow peptide exchange properties.

Adenosine Triphosphatases↗

PubMed1998

The photophobic receptor from Natronobacterium pharaonis: temperature and pH dependencies of the photocycle of sensory rhodopsin II.

The photocycle of the photophobic receptor sensory rhodopsin II from N. pharaonis was analyzed by varying measuring wavelengths, temperature, and pH, and by exchanging H2O with D2O. The data can be satisfactorily modeled by eight exponents over the whole range of modified parameters. The kinetic data support a model similar to that of bacteriorhodopsin (BR) if a scheme of irreversible first-order reactions is assumed. Eight kinetically distinct protein states can then be identified. These states are formed from five spectrally distinct species. The chromophore states Si correspond in their spectral properties to those of the BR photocycle, namely pSRII510 (K), pSRII495 (L), pSRII400 (M), pSRII485 (N), and pSRII535 (O). In comparison to BR, pSRII400 is formed approximately 10 times faster than the M state; however, the back-reaction is almost 100 times slower. Comparison of the temperature dependence of the rate constants with those from the BR photocycle suggests that the differences are caused by changes of DeltaS. The rate constants of the pSRII photocycle are almost insensitive to the pH variation from 9.0 to 5.5, and show only a small H2O/D2O effect. This analysis supports the idea that the conformational dynamics of pSRII controls the kinetics of the photocycle of pSRII.

Archaeal Proteins↗

PubMed1998

Long-term treatment of alpha1-antitrypsin deficiency-related pulmonary emphysema with human alpha1-antitrypsin. Wissenschaftliche Arbeitsgemeinschaft zur Therapie von Lungenerkrankungen (WATL)-alpha1-AT-study group.

Alpha1-antitrypsin (alpha1-AT) deficiency is a genetic disorder characterized by low serum levels of alpha1-AT and a high risk of pulmonary emphysema at a young age. The resulting surplus of proteases, mainly of neutrophil elastase, can be balanced by i.v. augmentation with alpha1-AT. However, it is not clear if affected patients benefit from long-term augmentation therapy and no long-term safety data are available. We examined 443 patients with severe alpha1-AT deficiency and pulmonary emphysema receiving weekly i.v. infusions of 60 mg x kg body weight(-1) alpha1-AT in addition to their regular medication. The progression of the disease was assessed by repeated lung function measurements, particularly the decline in forced expiratory volume in one second (deltaFEV1). Four hundred and forty three patients with alpha1-AT deficiency tolerated augmentation therapy well with few adverse reactions. The deltaFEV1 in 287 patients with available follow-up data was 57.1+/-31.1 mL x yr(-1). Stratified for baseline FEV1, the decline was 35.6+/-21.3 mL in the 108 patients with an initial FEV1 <30% and 64.0+/-26.4 mL in the 164 with FEV1 30-65% of predicted normal (p=0.0008). The remaining 15 patients had an initial FEV1 >65% pred. Long-term treatment with i.v. alpha1-antitrypsin in patients with severe alpha1-antitrypsin deficiency is feasible and safe. The decline in forced expiratory volume in one second is related to the initial forced expiratory volume in one second as in alpha1-antitrypsin deficient patients not receiving augmentation therapy.

Adult↗

PubMed1998

[Long-term therapy of alpha 1-antitrypsin-deficiency-associated pulmonary emphysema with human alpha 1-antitrypsin].

alpha 1-antitrypsin (alpha 1-AT) deficiency is a genetic disorder characterized by low serum levels of alpha 1-AT and a high risk of pulmonary emphysema at a young age. The resulting surplus of proteases, mainly of neutrophil elastase, can be balanced by i.v. augmentation with alpha 1-AT. However, it is not clear if affected patients benefit from long-term augmentation therapy and no long-term safety data are available. We examined 443 patients with severe alpha 1-AT deficiency and pulmonary emphysema receiving weekly i.v. infusions of 60 mg/kg body weight alpha 1-AT in addition to their regular medication. The progression of the disease was assessed by repeated lung function measurements, particularly the decline in forced expiratory volume in 1 second (delta FEV1). 443 patients with alpha 1-AT deficiency tolerated augmentation therapy well with few adverse reactions. The delta FEV1 in 287 patients with available follow-up data was 57.1 +/- 31.1 ml per year. Stratified for baseline FEV1, the decline was 35.6 +/- 21.3 ml in the 108 patients with an initial FEV1 < 30% and 64.0 +/- 26.4 ml in the 164 with 30% < FEV1 < or = 65% of predicted normal (p = 0.0008). The remaining 15 patients had an initial FEV1 > 65%. Long-term treatment with i.v. alpha 1-antitrypsin in patients with severe alpha 1-Pi deficiency is feasible and safe. The decline in forced expiratory volume in one second is related to the initial forced expiratory volume in one second as in alpha 1-antitrypsin deficient patients not receiving augmentation therapy.

Adult↗

PubMed1997

Prediction of low body weight at long-term follow-up in acute anorexia nervosa by low body weight at referral.

OBJECTIVE: The authors investigated the hypothesis that in acute anorexia nervosa a low body weight predicts a poor weight prognosis for the future. METHOD: The body mass indexes at referral of 272 female patients were examined in relation to the body mass indexes of these patients after a mean follow-up of 9.5 years. RESULTS: The overall correlation between body mass indexes at referral and at follow-up was r = 0.33. Despite this low correlation, the 100 patients with body mass indexes less than 13 kg/m2 at referral had low weights at long-term follow-up. Eleven of the 12 deceased patients were among these 100 patients, as were 24 of the 46 surviving patients whose body mass indexes were 17.5 kg/m2 or less at follow-up. CONCLUSIONS: For patients with anorexia nervosa, a body mass index less than 13 kg/m2 at referral indicates a substantial risk for chronic anorexia nervosa and death related to emaciation.

Acute Disease↗

PubMed1995

Observations of energetic particles with EPAC on Ulysses in polar latitudes of the heliosphere.

Measurements with the Energetic Particle Composition instrument (EPAC) aboard Ulysses show particles from near the ecliptic that were apparently accelerated by shocks associated with a corotating interaction region. The particles were detected together with the shocks and even when shocks no longer arrived at Ulysses up to -65 degrees of heliographic latitude but not beyond. Particles could have reached these latitudes along magnetic fields; such connections to the outer lower latitude heliosphere evidently do not exist above that latitude. The accelerated streams have composition similar to solar wind abundances, no dispersion, and a net inward anisotropy. The underlying composition between the recurrent stream is similar to the anomalous component of cosmic rays. The channel sensitive to high-energy protons (> 230 megaelectron volts) shows a 26-day variation of the flux superimposed on the heliospheric modulation of galactic ions.

Acceleration↗

PubMed1995

The primary structure of sensory rhodopsin II: a member of an additional retinal protein subgroup is coexpressed with its transducer, the halobacterial transducer of rhodopsin II.

The blue-light receptor genes (sopII) of sensory rhodopsin (SR) II were cloned from two species, the halophilic bacteria Haloarcula vallismortis (vSR-II) and Natronobacterium pharaonis (pSR-II). Upstream of both sopII gene loci, sequences corresponding to the halobacterial transducer of rhodopsin (Htr) II were recognized. In N. pharaonis, psopII and phtrII are transcribed as a single transcript. Comparison of the amino acid sequences of vHtr-II and pHtr-II with Htr-I and the chemotactic methyl-accepting proteins from Escherichia coli revealed considerable identities in the signal domain and methyl-accepting sites. Similarities with Htr-I in Halobacterium salinarium suggest a common principle in the phototaxis of extreme halophiles. Alignment of all known retinal protein sequences from Archaea identifies both SR-IIs as an additional subgroup of the family. Positions defining the retinal binding site are usually identical with the exception of Met-118 (numbering is according to the bacteriorhodopsin sequence), which might explain the typical blue color shift of SR-II to approximately 490 nm. In archaeal retinal proteins, the function can be deduced from amino acids in positions 85 and 96. Proton pumps are characterized by Asp-85 and Asp-96; chloride pumps by Thr-85 and Ala-96; and sensors by Asp-85 and Tyr-96 or Phe-96.

Amino Acid Sequence↗

PubMed1994

[The Berlin follow-up study of eating disorders in adolescence. Part 2: Intermediate-term catamnesis after 4 years].

After more than four years, ten patients in a cohort of 60 consecutively-assessed adolescent patients with eating disorders were no longer available for follow-up--four had died and six refused to participate further. The follow-up interviews indicated varying rates of impairment in relation to eating disorders, menstrual anomalies, sexuality and psychosocial functioning. The distribution of continuing disorders at follow-up was a) 10% anorexia nervosa, b) 4% anorexia nervosa with bulimia, c) 18% anorectic and bulimic partial syndromes. The remaining 68% were found to have recovered. During the course of illness, there were few instances of anorectic symptoms crossing over into bulimic ones. A uniform pattern in the disease course was observed throughout the various self-evaluation questionnaires: reduction of symptoms that occurred during the course of the inpatient treatment could also be observed at the time of the follow-up. As compared with the international literature on follow-up studies, these can be considered as favorable findings.

Adolescent↗

PubMed1994

[The Berlin follow-up study of eating disorders in adolescence. Part 3: Evaluation and prognosis].

This third report from the Berlin follow-up study of eating disorders in adolescence reports findings pertaining to evaluation and prognosis. Based on a systematic analysis of the relevant literature on the course of eating disorders, the following items were analyzed with respect to their value in predicting the psychopathological status of the patient at discharge from inpatient treatment and at follow-up: BMI at admission, age at onset of the disease, duration of symptoms before admission, personality features such as depression and neuroticism, the number of physical complaints, diagnosis (anorexia vs. bulimia), type of eating disorder (purger vs. restrictor), premorbid eating disorders or behavioral abnormalities, socioeconomic status, duration of in-patient treatment, and out-patient psychotherapy following discharge from the hospital. None of the factors predicted psychopathological status at either discharge or long-term follow-up.

Adolescent↗

PubMed1994

[Eating disorders in adolescents in East and West Berlin in the 80's].

Data collected in the 1980's, before the reunification of Germany, and comparing 39 patients in former East Berlin and 60 patients in former West Berlin are presented in this second report on the Berlin longitudinal study of eating disorders in adolescence. The clinical profiles of patients of former East Berlin were found to differ from those of their West Berlin counterparts in the following assessed measures: younger age at disease onset and at admission for inpatient treatment; greater number of siblings; fewer accounts of the clinical symptoms lanugo, bradycardia, hypothermia, constipation; lower rate of premorbid psychopathological features; lower number of psychopathological findings; less frequent sibling rivalry; lower rate of psychopathological attributes among the siblings; lower incidence of maternal mental and physical illness; higher parental educational status; fewer number of complaints, and better sense of well-being.

Adolescent↗

PubMed1993

Correspondence between the clinical assessment of eating-disordered patients and findings derived from questionnaires at follow-up.

Questionnaire scores were compared across three outcome groups in a follow-up of eating-disordered patients with onset of the disease during adolescence. Among a total of 40 patients, 7 continued to suffer from either anorexia or bulimia nervosa. Seven additional patients displayed partial syndromes and 26 had recovered. Both a semantic differential measuring body image and the Eating Attitudes Test (EAT) demonstrated limited evidence of clinical sensitivity by differentiating the three outcome groups. The Eating Disorders Inventory (EDI) did not discriminate the three outcome groups. Obviously, clinical interviews and self-report questionnaires tackle different facets of the eating disorders and, therefore, both should be used in outcome studies.

Adolescent↗