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Biomedical subjects

S Premilat

Publications and source records attributed to S Premilat.

At least 37 records · Page 2Linked to original sources
PubMed1986

DNA models for A, B, C and D conformations related to fiber X-ray, infrared and NMR measurements.

A conformational analysis of the A, B, C and D DNA forms was made in order to establish molecular models presenting a good agreement with experimental data obtained from fiber X-ray, infrared linear dichroism and 31P NMR. The proposed models have been refined and do present good stereochemistry and optimized H-bond distances between bases associated with the Watson-Crick pairing. The DNA conformations proposed are a left handed double helix for the C form and right handed helices for A, B and D. Relations to conformational transitions between these forms are discussed.

DNA↗
PubMed1986

Proposals for the mu-active conformation of the enkephalin analog Tyr-cyclol(-N gamma-D-A2-bu-Gly-Phe-Leu-).

The conformational behavior of the sterically restricted cyclic peptide Tyr-cyclo(-N gamma-D-A2-bu-Gly-Phe-Leu-), proposed recently as an enkephalin analog with high opiate activity, is examined by theoretical investigations. The method used allows the search of conformational energy minima associated with cyclic structures fitting a hypothetical opiate pharmacophore. The results obtained show that, despite the fact that many cyclic structures of low conformational energy can be found for this compound, only one of them can be retained as a conformer presenting the characteristic features of the imposed pharmacophore. This conformation is stabilized by an intramolecular H-bond between the D-A2bu-carbonyl and the Leu NH group so that a beta-turn is formed. This structure also presents a high mobility of the Tyr1 side-chain which can fit the tyramine moiety of rigid opiates with minor loss of conformational energy. A two-step binding mechanism is proposed for the interactions of this cyclic peptide with its receptor which could be an intermediate between the "zipper" model proposed for flexible linear peptides and the "lock-and-key" model adapted to rigid molecules. The selectivity of enkephalin analogs for mu and delta opioid receptors is discussed in light of the present theoretical investigations.

Enkephalin, Leucine↗
PubMed1985

A screened electrostatic potential model of hydration for conformational analysis of biomolecules.

A screened electrostatic potential model of hydration which could avoid the time consuming Monte-Carlo procedures is derived from the study of the dielectric effect of a water molecule in the vicinity of two charges. It is shown that the molecular dielectric constant depends on the distance, sizes and signs of the interacting charges. The model is used to evaluate the hydration energy of the tetrapeptide (TYR-GLY-GLY-PHE) conformations. Results are in good agreement with Monte-Carlo calculations.

Mathematics↗
PubMed1985

Fibre X-ray and conformational study of the binding of metal ions on DNA.

Results obtained from X-ray diffraction as well as from conformational analysis of Ag-DNA fibres are presented. For small percentages of Ag+ bound and high humidity, the B-DNA form is maintained. As the percentage of Ag+ is increased, the helical parameters of the B-DNA are modified. These modifications are directly related to the percentage of G-C bases. The periodicity of the DNA fibres are perturbed as Ag+ is mainly bound to G-C pairs and, thus, only the equatorial diffracted intensities can be compared to values calculated from molecular models. It is shown, by this way, that the first binding site is located on N7 of G. A second site is situated between N3 and N1 of the G-C pair, at the place of a hydrogen bond. A molecular model of the Ag-DNA complex is proposed and shown to be in agreement with experimental data. Results obtained allow to get some information on the binding of other ions such as Cu2+ and Hg2+ which give very little modification of the fibre X-ray patterns.

Base Composition↗
PubMed1984

Conformations of C-DNA in agreement with fiber X-ray and infrared dichroism.

Different left handed double helices are proposed as models for DNA fibers in the C form. These conformations have geometrical parameters which agree well with fiber X-ray data and the orientations of their phosphate groups are in good agreement with infrared dichroism results. A complete set of atomic coordinates and dihedral angles are given together with curves of calculated diffracted intensities. The present results are compared with experimental values and with the other C-DNA models.

Circular Dichroism↗
PubMed1983

Conformations of A-DNA and B-DNA in agreement with fiber X-ray and infrared dichroism.

Two right handed double helices are proposed as models for DNA fibers in respectively the A and the B form. The present conformations have geometrical parameters which agree very well with fiber X-ray and the orientation of their phosphate groups is in good accordance with infrared dichroïsm measurements. Dihedral angles and complete sets of atomic coordinates are given together with stereo-views and curves of the calculated diffracted intensities. Results are compared with experimental data and with preceding DNA models.

Circular Dichroism↗
PubMed1982

A critical analysis of a left-handed double helix model for B-DNA fibers.

A search for a left-handed double helix model for B-DNA fibers has been undertaken. The model has to present good stereochemistry and also to be in agreement with X-ray and infrared data. Dihedral angles as well as atomic coordinates and calculated intensities curves are given for the best model obtained. Comparison with experimental results shows that this model must be rejected as a candidate for the representation of B-DNA fibers.

DNA↗
PubMed1982

[A B-DNA conformation in agreement with X-ray from fibres and infrared data (author's transl)].

A right-handed double helix is proposed as a model for fibres of B-DNA. This conformation presents geometrical parameters which are in agreement with X-ray data as well as with infrared measurements. Dihedral angles and atomic coordinates are given together with curves of the calculated intensities. These results are compared with experimental values and with preceding models of the B-DNA.

DNA↗
PubMed1976

[X-ray diffraction study of the binding of Cu2+ and Ag2+ cations to DNA].

An X-ray diffraction study has been undertaken on fibres of two different DNA compositions respectively corresponding to 42 and 72% of (G-C) base percentages. The fibres were prepared after binding of copper or silver ions to the DNA gels. With a relative humidity of 92%, the B-form has been observed for these two DNA molecules in the presence of copper ions or with a low percentage of silver ion binding. When the silver ion percentage is increased, a new form appears. From the comparison between the experimental and calculated intensities one can note that the proposed binding sites for copper involve few modifications in the X-ray patterns. For the silver, the calculated intensities show that the metal atom is near the double helix axis. For low percentages of silver the site between successive guanine bases cannot be distinguished with certainty by intensity analysis.

Animals↗