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Accueil > Publications > Recherche par années > Années 1990 > 1999

1999

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Cytotoxicity and DNA binding mode of new platinum-iminoether derivatives with different configuration at the iminoether ligands

The platinum-iminoether complexes trans-[PtCl2E-HN=-C(OEt)Me(2)] (1) and trans-[PtCl2Z-HN=C(OEt)Me(2)] (2), differing in the configuration of the iminoether ligands, were investigated for cytotoxicity towards human tumor cell lines, the involvement of DNA as a cytotoxic target, and their DNA binding mode. The cytotoxicity of isomer 1 was comparable to that of cisplatin, whereas isomer 2 was slightly less active. Excision-repair-deficient xeroderma pigmentosum group A cells were four times more sensitive to both isomers than normal cells, thus implicating cellular DNA as the cytotoxic target. Replication mapping experiments showed that both isomers interact preferentially with guanine residues at py-G-py sites.

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Dimer initiation sequence of HIV-1(Lai) genomic RNA : NMR solution structure of the extended duplex

The genome of all retrovirus consists of two copies of genomic RNA which are noncovalently linked near their 5’ end. A sequence localized immediately upstream from the splice donor site inside the HIV-1 Psi-RNA region was identified as the domain responsible for the dimerization initiation. It was shown that a kissing complex and a stable dimer are both involved in the HIV-1(Lai) RNA dimerization process in vitro. The NCp7 protein activates the dimerization by converting a transient loop-loop complex into a more stable dimer. The structure of this transitory loop-loop complex was recently elucidated by Mujeeb et al.

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Dimer models for ErbB-2/neu transmembrane domains from molecular dynamics simulations

Interest in the transmembrane receptors tyrosine kinase of the erbB family is high due to the involvement of some of the members in human cancers. The original oncogenic alleles of neu discovered in rat neuroectodermal tumors lead to single Va1664Glu substitution within the predicted transmembrane domain : Identical substitution at the homologous position 659 constitutively activates the oncogenic potential of the human ErbB-2 receptor by enhanced receptor dimer formation. The precise molecular details of receptor dimerization are still unknown and to acquire more knowledge of the mechanisms involved, molecular dynamics simulations are undertaken to study transmembrane dimer association. Transmembrane helices are predicted to associate in left-handed coiled-coil structures stabilized by Glu-Glu interhelix hydrogen bonds in the mutated form. The internal dynamics reveals pi helix deformations which modify the helix-helix interface. Predicted models agree with those suggested from polarized IR and magic-angle spinning NMR spectroscopy.

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DNA bending induced by the archaebacterial histone-like protein MC1

The conformational changes induced by the binding of the histone-like protein MC1 to DNA duplexes have been analyzed by dark-field electron microscopy and polyacrylamide gel electrophoresis. Visualisation of the DNA molecules by electron microscopy reveals that the binding of MC1 induces sharp kinks. Linear DNA duplexes (176 bp) which contained a preferential site located at the center were used for quantitative analysis. Measurements of the angle at the center of all duplexes, at a fixed DNA concentration, as a function of the MC1 concentration, were very well fitted by a simple model of an isotropic flexible junction and an equilibrium between the two conformations of DNA with bound or unbound MC1.

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Domain-domain interactions in high mobility group 1 protein (HMG1)

The high mobility group protein HMG1 is a conserved chromosomal protein with two homologous DNA-binding domains, A and B, and an acidic carboxy-terminal tail, C. The structure of isolated domains A and B has been previously determined by NMR, but the interactions of the different domains within the complete protein were unknown. By means of differential scanning calorimetry and circular dichroism we have investigated the thermal stability of HMG1, of the truncated protein A-B (HMG1 without the acidic tail C) and of the isolated domains A and B. In 3 mM sodium acetate buffer, pH 5, the thermal melting of domains A and B are identical (transition temperature t(m) = 43 degrees C and 41 degrees C, denaturation enthalpies Delta H = 46 kcal.mol(-1)).

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Dynamics of the transmembrane domain of the ErbB-2 receptor

The structure and dynamics of the ErbB-2 transmembrane domain have been examined using molecular dynamics techniques both in Vacuum and within an explicit hydrated L-alpha-dilauroyl-phosphatidyl-ethanolamine environment. In-vacuum simulations show that a highly cooperative structural transition occurs frequently within the alpha-helical transmembrane domain which converts to local pi-helices. We show that the alpha-helix alteration does not depend upon the force field or initial side-chain conformations but is intimately related to the sequence. The membrane-like environment does not prevent the structural transition in the helix but slows down the peptide dynamics indicating that the appearance of a pi-bulge is not an artifact of the Vacuum approximation. The consequences of pi-helix formation could be very huge for the ErbB-2 receptor which is involved in numerous human cancers and also for other membrane proteins wherein similar local structures are also observed experimentally.

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Efficient gene transfer by histidylated polylysine pDNA complexes

Plasmid/polylysine complexes, which are used to transfect mammalian cells, increase the uptake of DNA, but plasmid molecules are sequestered into vesicles where they cannot escape to reach the nuclear machinery. However, the transfection efficiency increases when membrane-disrupting reagents such as chloroquine or fusogenic peptides, are used to disrupt endosomal membranes and to favor the delivery of plasmid into the cytosol. We designed a cationic polymer that forms complexes with a plasmid DNA (pDNA) and mediates the transfection of various cell lines in the absence of chloroquine or fusogenic peptides.

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