Biomedical subjects

M Dathe

Publications and source records attributed to M Dathe.

29 records · Page 2Linked to original sources

PubMed1996

Conformational and functional study of magainin 2 in model membrane environments using the new approach of systematic double-D-amino acid replacement.

Systematic double-D-amino acid replacement of adjacent amino acids has been used to study the secondary structure of the amphiphilic, antibiotic peptide magainin 2 amide (M2a) by circular dichroism spectroscopy. Bound to liposomes, the secondary structure of the peptide is characterized by a weak alpha-helix in the N-terminus and a stable alpha-helix between residues 9 and 21. The lack of conformational differences in the peptide when bound to vesicles of varying negative charge density indicates marked independence of the structure from electrostatic forces. The similarity of the helicity profiles observed for double D-isomers bound to vesicles and in the presence of sodium dodecyl sulfate micelles (SDS) clearly shows that SDS can mimic magainin-lipid interactions. In contrast, in 1:1 trifluoroethanol/buffer (v/v), the peptide exhibits a weak alpha-helix extended from the N- to the C-terminus. Dye release experiments from vesicles of phosphatidylglycerol showed that double-D-amino acid substitution only in the region of the stable helix results in a reduction of the membrane-permeabilizing ability. On vesicles with a reduced amount of acidic phospholipids, double-D-amino acid substitution in any position leads to a drastic reduction of peptide-induced membrane permeabilization. Whereas the activity of M2a on phosphatidylglycerol was found to be mainly electrostatically determined, hydrophobic interactions play a decisive role in the interaction with vesicles of reduced negative charge density. Fluorescence investigations of tryptophan-containing analogs of high and low helicity showed that differences in the location of the chromophores of the membrane-bound peptides do not exist.

Amides↗

PubMed1996

Confidence intervals for calibration with neural networks.

Based on neural network calibration the confidence intervals of aromaticity determination from infrared reflectance spectra of raw brown coals were estimated by means of the bootstrap method, a simplified Monte Carlo Simulation. The standard deviations and the confidence intervals were estimated to characterise the analysis error.It is shown that confidence intervals of non-linear analysis methods like Back Propagation Neural Networks (BPNN) can be estimated by the bootstrap method. The estimated confidence intervals of the calibration confirm the analysis by BPNN.

Journal Article↗

PubMed1996

Conformation of a water-soluble beta-sheet model peptide. A circular dichroism and Fourier-transform infrared spectroscopic study of double D-amino acid replacements.

Among peptide secondary structures beta-sheet domains have been much less intensively studied than alpha-helical conformations, mainly because of the lack of well characterized model peptides. In the present paper the secondary structure of a water-soluble de novo peptide consisting of 26 amino acids (DPKGDPKGVTVTVTVTVTGKGDPKPD-NH2) and the corresponding double D-amino acid replacement set have been studied by circular dichroism and Fourier-transform infrared spectroscopy. The model peptide was found to be unstructured in aqueous solution at peptide concentrations < 10(-3) mol/L but to adopt a predominantly beta-sheet structure in the presence of 15 mM sodium dodecyl sulfate or at apolar/water interfaces. Although the peptide is composed of amino acids with low helical propensity, it formed a single-stranded helical structure in aqueous trifluoroethanol. The D-amino acid replacement set was synthesized in order to study the conformational stability of the model peptide selectively in distinct regions. The data show that both the alpha-helix present in 50% trifluoroethanol as well as the beta-sheet domain formed in the presence of sodium dodecyl sulfate or at apolar/water interfaces, are located in the region between Val9 and Thr18. Pairwise substitution of adjacent amino acids by their corresponding D-amino acids provides a pronounced beta-sheet disturbance. These findings demonstrate that double D-amino acid replacements may be used to locate beta-sheet domains in peptides.

Amino Acid Sequence↗

PubMed1996

Conformational differences of ovine and human corticotropin releasing hormone. A CD, IR, NMR and dynamic light scattering study.

The differences in the conformational properties of ovine (o) and human (h) CRH in aqueous solution, structure-inducing TFE and in the presence of detergent micelles and lipid vesicles have been investigated by circular dichroism, Fourier transform infrared spectroscopy, NMR and dynamic light scattering. o-CRH was found to exist as a monomer with little regular structure in dilute aqueous solution. Association at concentrations higher than 10-3 mol/L results predominantly in dimers. The induction of a substantial amount of intermolecular beta-structure seems to be the result of interactions of the C-terminal hexapeptide and the N-terminal region 6-12 of o-CRH chains in antiparallel orientation. In contrast, h-CRH exhibits a high tendency of association which is highly sensitive to the pH. The formation of tetramers at millimolar peptide concentration is related to a helical content of ca. 50%. The potentially helical, highly hydrophobic region 6-20 enlarged by more hydrophobic residues in position 23 and 25 is proposed to stabilize the h-CRH associates. In the presence of structure inducing TFE (> 40% v) both CRH peptides exist as monomers. o-CRH reveals about 72% helicity, in h-CRH the formation of about 85% helix is observed. The differences in helicity of the two CRH molecules are located in the C-terminal heptapeptide, as concluded on the basis of NMR studies. Both peptides bind to detergent micelles at pH 4 as well as 7.4 associated with an increase in the alpha-helical content. Interaction of the two peptides with DMPC vesicles was found exclusively at pH 4. Above the phase transition temperature of DMPC the alpha-helical content in h-CRH increases slightly; however, o-CRH reveals a substantial amount of beta-type structure. The intramolecular type of beta-structure is associated with a deeper insertion of the o-CRH region 6-12 into the hydrophobic region of the lipid bilayer, whereas the corresponding region of h-CRH is kept in the bilayer surface. The higher helicity of h-CRH might explain to some extent its higher affinity to the CRH receptor, CRH antibodies and the CRH binding protein.

Animals↗

PubMed1995

Influence of alpha-helicity, amphipathicity and D-amino acid incorporation on the peptide-induced mast cell activation.

Mast cell activation by polycationic substances is believed to result from a direct activation of G protein alpha subunits and it was suggested that the adaption of amphipathic, alpha-helical conformations would allow the peptide to reach the cytosolic compartment to interact with G proteins (Mousli et al., 194, Immunopharmacology 27, 1, for review). We investigated the histamine-releasing activity of model peptides as well as analogues of magainin 2 amide and neuropeptide Y with different amphipathicities and alpha-helix content on rat peritoneal mast cells. Amphipathic helicity is not a prerequisite for mast cell activation. Moreover, non-helical magainin peptides with high histamine-releasing activity were less active in the liberation of carboxyfluoresceine from negatively charged liposomes, indicating that peptide-induced mast cell activation and peptide-induced membrane perturbation do not correlate. In contrast to the negligible influence of the secondary structure, amino acid configuration may exert a striking influence on peptide-induced mast cell activation. Thus histamine-release by substance P was markedly impaired when the L-amino acids in the positively charged N-terminal region were replaced by D-amino acids, with [D-Arg1)substance P being the most inactive substance P diastreoisomer.

Amino Acid Sequence↗

PubMed1995

Location of an amphipathic alpha-helix in peptides using reversed-phase HPLC retention behavior of D-amino acid analogs.

The reversed-phase HPLC retention behavior of D-amino acid replacement sets of an amphipathic model peptide, neuropeptide Y, and corticotropin releasing factor has been studied. The results demonstrate that D-amino acid substitutions destabilized the amphipathic alpha-helix, leading to a decrease of fractional helicity as determined by circular dichroism. The effect is enhanced by substitution of two adjacent D-amino acids and correlates well with a decrease of hydrophobic interaction during reversed-phase HPLC, caused by disturbance of the preferred binding domain of the stationary phase-bound peptide. In contrast, D-amino acid substitutions in nonamphipathic or disordered regions of peptides do not influence the retention time to the same extent. Thus, the "retention profile" that results from plotting the retention time vs the position of the double D-amino acid replacements provides an indication of the presence and location of an amphipathic alpha-helical secondary structure in peptides.

Amino Acid Sequence↗

PubMed1995

Recognition of alpha-helical peptide structures using high-performance liquid chromatographic retention data for D-amino acid analogues: influence of peptide amphipathicity and of stationary phase hydrophobicity.

The reversed-phase HPLC behaviour of double D-amino acid replacement sets of amphipathic and non-amphipathic helix-forming peptides consisting exclusively of leucine, lysine and alanine residues was studied on different polymer-encapsulated silica-based stationary phases. Plotting the retention times versus the position of D-amino acid substitution gives a characteristic pattern showing decreased retention times in the helical region. The retention time profile obtained using an amphipathic alpha-helix is caused by disturbance of the preferred binding domain of the stationary phase-bound peptide. However, the effect is similar but less pronounced using a non-amphipathic helical peptide that is unable to interact by a preferred binding site. The results demonstrate that reversed-phase HPLC data for peptide analogues provide an indication event of a non-amphipathic helical structure in peptides.

Amino Acid Sequence↗

PubMed1992

[Potential cardiotonics. 15. Crystal modifications of 3-cyano-2-morpholino-5-(4-pyridinyl)pyridine (AWD 122-14)].

The preparation and X-ray crystallographic characterisation of 10 polymorphic or pseudo-polymorphic forms of the novel cardiotonic AWD 122-14 are described. Thermic transformations of some polymorphic forms into the alpha-form was proved by thermogravimetric analysis and powder diffraction pattern. In dissolution behaviour no significant differences were found between the crystalline modifications but with regard to galenic processing compact alpha-, gamma- and epsilon-forms show advantages.

Cardiotonic Agents↗

PubMed1990

Insulin aggregation in solution.

The process of insulin aggregation in neutral solutions was studied by dynamic light scattering. Solutions of different concentrations were subjected to thermal and mechanical stress (37 degrees, rotation) for a period of 4 weeks. The starting solutions contained exclusively one particle distribution of insulin in the association equilibrium with hexamers as the largest structures. After a lag period of about 8 days the solutions showed continuously increasing scattering intensities but did not evolve perceptible turbidity within the experimental period. A more rapid increase in scattering intensity was observed in diluted than in concentrated solutions. The analysis of scattering data unexpectedly revealed that insulin species did not grow continuously. After the lag period one additional relatively restricted size distribution with particles of a mean radius of about 100 nm was found, the amount of which increased continuously with time. The occurrence of these particles seems to be related to adsorption phenomena of insulin to the solid interface. We assume the 100 nm-class of aggregates to be a transient state in the physical destabilization process of insulin solutions.

Humans↗

PubMed1988

[Crystal modifications of 3-cyan-6-methyl-5-(pyrid-4-yl)-1,2-dihydropyrid-2-one (milrinone)].

The preparation and characterisation of crystalline alpha-, beta- and gamma modifications of 3-cyan-6-methyl-5-(4-pyrid-4-yl)-1,2-dihydropyrid-2-on e are described. The thermic transformation of alpha- and beta-modification into gamma-modification was proved by thermogravimetric analysis (t.g.a.), differential scanning calorimetry (d.s.c.), IR and powder diffraction pattern. In dissolution behaviour no significant differences were found between the modifications.

Chemical Phenomena↗

PubMedDate not supplied

Peptide destabilization by two adjacent D-amino acids in single-stranded amphipathic alpha-helices.

We recently described the local destabilizing effect of systematic double D-amino acid replacements for characterization of amphipathic helices in peptides. The objective of this study was to determine the destabilizing effect of two adjacent D-amino acids incorporated into the center of a single-stranded amphipathic alpha-helix by hydrogen exchange and guanidine hydrochloride denaturation studies in trifluoroethanol (TFE)/water. Data from guanidine hydrochloride titration experiments in the presence of 30% TFE suggest that double D-amino acid replacements at the center of the helix destabilize the secondary structure by 4.5 kJ/mol. While the exchange rate for one backbone proton was found to vary by a factor of 10 at the replacement position, the remaining backbone protons are not markedly influenced by double D-amino acid replacement. These results confirm the hypothesis that the energy of -4.5 kJ/mol per residue is a major contribution to the stability of helical peptides in water and in solvent mixtures of TFE/water.

Amino Acid Sequence↗