How ionic strength affects the conformational behavior of human and rat beta amyloids--a computational study.

Progressive cerebral deposition of amyloid beta occurs in Alzheimers disease and during the aging of certain mammals (human, monkey, dog, bear, cow, cat) but not others (rat, mouse). It is possibly due to different amino acid sequences at positions 5, 10 and 13. To address this issue, we performed series of 100 ns long trajectories (each trajectory was run twice with different initial velocity distribution) on amyloid beta (1-42) with the human and rat amino acid sequence in three different environments: water with only counter ions, water with NaCl at a concentration of 0.15 M as a model of intracellular Na(+) concentration at steady state, and water with NaCl at a concentration of 0.30 M as a model of intracellular Na(+) concentration under stimulated conditions. We analyzed secondary structure stability, internal hydrogen bonds, and residual fluctuation. It was observed that the change in ionic strength affects the stability of internal hydrogen bonds. Increasing the ionic strength increases atomic fluctuation in the hydrophobic core of the human amyloid, and decreases the atomic fluctuation in the case of rat amyloid. The secondary structure analyses show a stable α-helix part between residues 10 and 20. However, C-terminus of investigated amyloids is much more flexible showing no stable secondary structure elements. Increasing ionic strength of the solvent leads to decreasing stability of the secondary structural elements. The difference in conformational behavior of the three amino acids at position 5, 10 and 13 for human and rat amyloids significantly changes the conformational behavior of the whole peptide

Allopregnanolone and pregnanolone analogues modified in the C ring: Synthesis and activity

El pdf es la versión post-print.(25R)-3β-Hydroxy-5α-spirostan-12-one (hecogenin) and 11α-hydroxypregn-4-ene-3,20-dione (11α-hydroxyprogesterone) were used as starting materials for the synthesis of a series of 11- and 12-substituted derivatives of 5ξ-pregnanolone (3α-hydroxy-5α- pregnan-20-one and 3α-hydroxy-5β-pregnan-20-one), the principal neurosteroid acting via γ-aminobutyric acid (GABA). These analogues were designed to study the structural requirements of the corresponding GABA A receptor. Their biological activity was measured by in vitro test with [3H]flunitrazepam as radioligand in which allopregnanolone and its active analogues stimulated the binding to the GABAA receptor. Analysis of the SAR data suggests dependence of the flunitrazepam binding activity on the hydrophobic-hydrophilic balance of the groups at the C-ring edge rather than on specific interactions between them and the receptor. © 2013 American Chemical Society.This work was supported by Czech Grant 303/12/1464, Research Project of the AS CR RVO 61388963, and the Spanish Grants PI 061212 and PI 10/0453 from the Ministries of Health and of Science and Innovation, Grant 2009/SGR/214 from the Generalitat of Catalunya, and Grant 2006CZ0025 from CSIC.Peer Reviewe

Allopregnanolone (3α-Hydroxy-5α-pregnan-20-one) derivatives with a polar chain in position 16α: Synthesis and activity

The lipophilic nature of allopregnanolone prevents its user-friendly application in human medicine. On inspiration by pReviously prepared allopregnanolone with a 16α -bound tetraethylammonium salt, an attempt was made to produce allopregnanolone analogues with polar groups introduced into position 16α with the goal of increasing water solubility, brain accessibility, and potency of neuroactive steroids. The Michael addition to derivatives of pregn-16-en-20-one was the key reaction step. The link between the steroid skeleton and the new side chain was either a methylene group (when diethyl malonate was added) or an oxygen atom (when a hydroxy derivative was added). [35S]TBPS displacement was used to evaluate the products. Several carbamates (but not their parent alcohols) displaced TBPS from the picrotoxin binding site on GABAA receptors. Although none of them was more potent than the above ammonium salt, which stimulated this study, their nonionic nature should not prevent their passage into the brain. © 2009 American Chemical Society.Fil: Slavíková, Barbora. Academy of Sciences of the Czech Republic; República ChecaFil: Krištofíková, Zdena. Prague Psychiatric Centre; República ChecaFil: Chodounská, Hana. Academy of Sciences of the Czech Republic; República ChecaFil: Buděšínský, Miloš. Academy of Sciences of the Czech Republic; República ChecaFil: Duran, Fernando Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad de Microanálisis y Métodos Físicos en Química Orgánica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Unidad de Microanálisis y Métodos Físicos en Química Orgánica; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; ArgentinaFil: Veleiro, Adriana Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad de Microanálisis y Métodos Físicos en Química Orgánica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Unidad de Microanálisis y Métodos Físicos en Química Orgánica; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; ArgentinaFil: Burton, Gerardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad de Microanálisis y Métodos Físicos en Química Orgánica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Unidad de Microanálisis y Métodos Físicos en Química Orgánica; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; ArgentinaFil: Kasal, Alexander. Academy of Sciences of the Czech Republic; República Chec