Biomedical subjects

A Böckmann

Publications and source records attributed to A Böckmann.

11 recordsLinked to original sources

PubMed2003

Transverse dephasing optimized solid-state NMR spectroscopy.

It is shown how coherence lifetimes in solid-state NMR experiments can be controlled. New decoupling schemes are introduced which actively optimize dephasing times, providing increases of up to a factor of 2 with respect to the best existing schemes. The new schemes are implemented in transverse-dephasing-optimized (TDOP) NMR experiments for the disorded solid cellulose, and for a microcrystalline protein, where sensitivity improvements of up to a factor of 5 are obtained.

Bacillus subtilis↗

PubMed2000

Involvement of electrostatic interactions in the mechanism of peptide folding induced by sodium dodecyl sulfate binding.

Sodium dodecyl sulfate (SDS) has consistently been shown to induce secondary structure, particularly alpha-helices, in polypeptides, and is commonly used to model membrane and other hydrophobic environments. However, the precise mechanism by which SDS induces these conformational changes remains unclear. To examine the role of electrostatic interactions in this mechanism, we have designed two hydrophilic, charged amphipathic alpha-helical peptides, one basic (QAPAYKKAAKKLAES) and the other acidic (QAPAYEEAAEELAKS), and their structures were studied by CD and NMR. The design of the peptides is based on the sequence of the segment of residues 56-70 of human platelet factor 4 [PF4(56-70), QAPLYKKIIKKLLES]. Both peptides were unstructured in water, and in the presence of neutral, zwitterionic, or cationic detergents. However, in SDS at neutral pH, the basic peptide folded into an alpha-helix. By contrast, the pH needed to be lowered to 1.8 before alpha-helix formation was observed for the acidic peptide. Strong, attractive electrostatic interactions, between the anionic groups of SDS and the cationic groups of the lysines, appeared to be necessary to initiate the folding of the basic peptide. NMR analysis showed that the basic peptide was fully embedded in SDS-peptide micelles, and that its three-dimensional alpha-helical structure could be superimposed on that of the native structure of PF4(56-70). These results enabled us to propose a working model of the basic peptide-SDS complex, and a mechanism for SDS-induced alpha-helical folding. This study demonstrates that, while the folding of peptides is mostly driven by hydrophobic effects, electrostatic interactions play a significant role in the formation and the stabilization of SDS-induced structure.

Amino Acid Sequence↗

PubMed1998

Characterization of the interaction between bovine pancreatic trypsin inhibitor and thiocyanate by NMR.

The interaction between Bovine Pancreatic Trypsin Inhibitor and thiocyanate was studied using NMR spectroscopy following several experimental approaches. The chemical shift variations of the BPTI protons in the absence and in the presence of increasing thiocyanate concentrations (up to 0.2 M) were significant (> 0.05 ppm) for 30 protein protons belonging to 20 residues. The largest deviation, 0.2 ppm, was observed for the amide backbone proton of Arg42 in the absence of thiocyanate and in the presence of 40 molar equivalents of thiocyanate. The influence of the presence of thiocyanate on the electrostatic potential surrounding the protein was demonstrated by NOESY spectra selective at the water frequency: the presence of SCN- favours acid catalysed exchange and disfavours base catalysis. However, a specific effect of thiocyanate was pointed out since the comparison of the chemical shifts in the presence of 40 molar equivalents of KSCN and KCl, respectively, showed much more as well as larger deviations compared to measurements in the absence of salt. A dissociation constant, KD, for a 1/1 complex between BPTI and thiocyanate was calculated from chemical shifts measurements: KD = 89 +/- 8 mM. A second value, KD = 99 +/- 10 mM, was extracted from SC15N relaxation time measurements.

Animals↗

PubMed1997

Determination of fast proton exchange rates of biomolecules by NMR using water selective diffusion experiments.

We present a new water selective pulse sequence allowing rapid determination of exchange rates of labile protons on the millisecond time scale. Using diffusion measurements, exchange rates of resolved protons can be determined without prior knowledge of relaxation parameters in a short overnight experiment. The use of a sensitive, highly selective and easy to implement water excitation scheme allows for its straightforward application to a wide range of biomolecules. The results obtained for the imino proton exchange rates of a 16 bp DNA are in strong agreement with values obtained by the classical approach of two-dimensional exchange spectroscopy.

Base Sequence↗

PubMed1997

Three-dimensional structure of the DNA-binding domain of the fructose repressor from Escherichia coli by 1H and 15N NMR.

FruR is an Escherichia coli transcriptional regulator that belongs to the LacI DNA-binding protein family. By using 1H and 15N NMR spectroscopy, we have determined the three-dimensional solution structure of the FruR N-terminal DNA-binding domain consisting of 57 amino acid residues. A total of 809 NMR-derived distances and 54 dihedral angle constraints have been used for molecular modelling with the X-PLOR program. The resulting set of calculated structures presents an average root-mean-square deviation of 0.37 A at the main-chain level for the first 47 residues. This highly defined N-terminal part of the structure reveals a similar topology for the three alpha-helices when compared to the 3D structures of LacI and PurR counterparts. The most striking difference lies in the connection between helix II and helix III, in which three additional residues are present in FruR. This connecting segment is well structured and contains a type III turn. Apart from hydrophobic interactions of non-polar residues with the core of the domain, this connecting segment is stabilised by several hydrogen bonds and by the aromatic ring stacking between Tyr19 of helix II and Tyr28 of the turn. The region containing the putative "hinge helix" (helix IV), that has been described in PurR-DNA complex to make specific base contacts in the minor groove of DNA, is unfolded. Examination of hydrogen bonds highlights the importance of homologous residues that seem to be conserved for their ability to fulfill helix N and C-capping roles in the LacI repressor family.

Amino Acid Sequence↗

PubMed1996

Rapid estimation of relative amide proton exchange rates of 15 N-labelled proteins by a straightforward water selective NOESY-HSQC experiment.

A straightforward heteronuclear pseudo-3D NOESY-HSQC pulse sequence using radiation damping to selectively invert magnetization at the water frequency was developed to estimate the amide proton exchange rates in 15N-labelled proteins. The peak intensities in the resultant 2D spectrum allow a direct classification of amide proton exchange rates according to short (ms), intermediate (ms to s) or long (> or = s) residence times. This method was successfully used for the analysis of amide proton exchange rates in the 15N-labelled FruR DNA-binding domain and pertinent information about its dynamics was obtained.

Amides↗

PubMed1995

Body fat distribution and steroid hormone concentrations in obese adolescent girls before and after weight reduction.

The aim of this study was to investigate the role of body fat distribution on steroid hormone serum concentrations in obese adolescent girls before and after weight reduction. Ninety-two girls (age, 15.1 +/- 0.7 yr) with a mean body mass index of 31.2 +/- 4.6 kg/m2 participated in this 6-week intervention study. Initially, girls with abdominal obesity (waist to hip ratio, > 0.86; n = 30) had higher levels of total and free testosterone and lower levels of sex hormone-binding globulin as well as lower morning levels of total and free cortisol than girls with gluteal-femoral obesity (waist to hip ratio, < 0.80; n = 31) independent of their body mass index. After a mean weight loss of 8.3 +/- 2.6 kg by a standardized weight loss program, significant reductions were observed in estradiol, total and free testosterone, dehydroepiandrosterone sulfate, and the ratio of LH to FSH, whereas sex hormone-binding globulin and free cortisol levels increased significantly. Decreases in total and free testosterone and increases in total and free cortisol were significantly greater in the girls with abdominal obesity than in the girls with gluteal-femoral obesity. Our results suggest that obese girls with an abdominal pattern of fat distribution exhibit more pronounced steroid hormone aberrations, in particular a high androgenic activity, than girls with a gluteal-femoral pattern of fat distribution. The reduction of excess body weight by a conventional treatment regimen is associated with a remarkable improvement of steroid hormone abnormalities in this particular subtype of obese adolescent girls.

Adipose Tissue↗

PubMed1994

Body-fat distribution and changes in the atherogenic risk-factor profile in obese adolescent girls during weight reduction.

We examined the effect of the pattern of body-fat distribution on the modification of atherogenic risk factors in obese adolescent girls during weight reduction. During the 6-wk program, which included a mixed diet of 4321 kJ/d and intensive physical exercise, the girls lost 8.5 +/- 2.4 kg and their waist-to-hip ratio (WHR) decreased from 0.86 +/- 0.05 to 0.81 +/- 0.05 (P < 0.01). Significant reductions were observed for total cholesterol, LDL cholesterol, uric acid, fasting insulin, and systolic and diastolic blood pressure. Girls with abdominal obesity (WHR > 0.88) had greater reductions in serum cholesterol, LDL cholesterol, and uric acid than did girls with gluteal-femoral obesity (WHR < 0.81). In a multivariate-regression analysis these differences could be partly explained by the greater weight loss of the girls with abdominal obesity. These results suggest that during weight reduction girls with abdominal obesity exhibit more beneficial changes in the atherogenic-risk-factor profile than do girls with gluteal-femoral obesity, partly because of a greater weight loss.

Adipose Tissue↗

PubMed1994

New perspectives in the treatment of acute myeloid leukemia by hematopoietic growth factors.

The application of hematopoietic growth factors in the treatment on acute myeloid leukemia (AML) may principally aim at shortening the period of treatment associated neutropenia and reducing the rate of infectious complications by their post-therapeutic administration but may also be used to increase the sensitivity of leukemic blasts to antileukemic therapy by pretherapeutic growth stimulation. Both aspects were addressed in subsequent clinical phase II studies and preclinical investigations. In a first clinical trial, 36 patients with high-risk AML received granulocyte-macrophage colony-stimulating factor (GM-CSF) after successful cytoreductive chemotherapy and experienced a shortening of the period of post-therapeutic neutropenia by 6 to 9 days, leading to a significant reduction of treatment-associated deaths from 39% to 14%. In preclinical studies an enhancement of the cytotoxicity of cytosine arabinoside (AraC) on leukemic blasts could be shown by pretreatment with GM-CSF or IL-3. Investigations on the impact of hematopoietic growth factors on the intracellular metabolism of AraC indicated that this effect was primarily mediated by an increase in the activity of DNA-polymerase-alpha. The evaluation of different doses of AraC showed the most marked increase after the combination of GM-CSF with conventional rather than high doses of AraC. Based on these preclinical experiments, a prospective randomized trial was subsequently initiated investigating the effect of GM-CSF before and during induction, consolidation, and the first two cycles of maintenance chemotherapy in newly diagnosed AML. This ongoing trial has enrolled 67 patients at the current time. An early interim analysis showed no differences in remission rates but a tendency toward a longer remission duration in patients receiving GM-CSF. These data indicate that hematopoietic growth factors like GM-CSF in particular may provide a new perspective in the treatment of acute myeloid leukemia with the possibility of reducing treatment associated mortality and perhaps of increasing the efficacy of antileukemic treatment.

Acute Disease↗

PubMed1992

The relationship between body fat distribution and weight loss in obese adolescent girls.

Recent studies have demonstrated an association between the pattern of body fat distribution and the occurrence of cardiovascular risk factors. In this study, we evaluated changes in body fat distribution as defined by several anthropometric criteria during a six week weight reduction programme in 110 obese adolescent girls (mean age 15.2 +/- 0.4 years). The standardized regimen included a mixed diet of 1032 kcal/day and a daily exercise programme of 1-2 h duration. The mean weight loss was 8.6 +/- 2.8 kg, decreasing the body mass index (BMI) from 31.4 +/- 4.7 to 28.2 +/- 4.9 kg/m2 (P < 0.01). The reduction in body weight was accompanied by a significant decrease in the waist-to-hip ratio (WHR) from 0.86 +/- 0.06 to 0.81 +/- 0.05 (P < 0.01). The initial WHR was correlated with the degree of weight loss independent of the initial weight (r = 0.34, P < 0.001). Categorized according to the waist-to-hip ratio girls in the upper tertile (WHR > 0.88) lost significantly more weight than girls in the lower tertile (WHR < 0.80) (9.8 +/- 2.7 vs. 6.8 +/- 2.5 kg, P < 0.01). These findings suggest that girls with an abdominal type of obesity benefit more from a weight reduction programme than girls with a gluteal-femoral type of obesity.

Adipose Tissue↗

PubMed1988

Human recombinant granulocyte macrophage colony stimulating factor (GM-CSF) treatment of patients with acute leukemias in aplasia and at high risk of early death.

In the first clinical study on GM-CSF in acute leukemias continuous infusion of the growth factor is given to patients in aplasia and at high risk of early death due to age over 65 years and/or intensive chemotherapy for resistance or relapse. Among 6 patients (4 AML, 2 ALL) receiving a total of 7 courses two died too early to contributing adequate data. Three patients and 4 courses showed earlier neutrophil recovery than related control groups and a fourth patient with secondary AML showed a neutrophil recovery time in the normal range, but much shorter than her platelet and reticulocyte recovery. No evidence was obtained so far for leukemic regrowth in these patients including blood and bone marrow cytology, monitoring of DNA aneuploidy by flow cytometry and clonogenic cells by colony assays. Thus, GM-CSF may be useful for rescue after intensive chemotherapy of AML and ALL and may not necessarily increase the risk of leukemia progression.

Aged↗