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

1999

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The nature of fossil bacteria : A guide to the search for extraterrestrial life

In an attempt to establish reliable criteria for the identification of potential fossil life in extraterrestrial materials, the fossilizable characteristics of bacteria, namely, size, shape, cell wall texture, association, and colony formation, are described, and an overview is given of the ways in which fossil bacteria are preserved las compressions in fine-grained sediments ; preservation in amber ; permineralized by silica ; replacement by minerals such (as silica, pyrite, Fe/Mn oxides, calcite, phosphate, and siderite ; or as molds in minerals). The problem of confounding minerally replaced bacteria with non biological structures having a bacterial morphology is addressed. Examples of fossilized bacteria from the Early Archaean through to the Recent are used to illustrate the various modes of preservation and the morphology of fossil bacteria.

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The nuclear export signal-dependent localization of oligonucleopeptides enhances the inhibition of the protein expression from a gene transcribed in cytosol

Upon endocytosis, most oligodeoxynucleotides (ODNs) accumulate in vesicular compartments ; a tiny number of them cross the vesicle membrane, reach the cytosol and by passive diffusion enter the nucleus where they are entrapped. So far, the compartment in which an antisense ODN interacts with its mRNA target has not been precisely characterized. In an attempt to answer this question, ODN-peptides were designed with the aim of maintaining them in the cytosol, This has been achieved by a short peptide sequence called the nuclear export signal (NES). Upon microinjection, ODN-NES peptide conjugates were efficiently and rapidly exported from the nucleus to the cytosol whereas ODN-peptides containing an inactive NES were found to be located in the nucleus. The inhibitory activity of antisense ODN was tested in a system allowing the specific transcription of a luciferase reporter gene in the cytosol, Antisense propynylated ODN-NES peptide conjugates, directed against the luciferase gene, efficiently inhibited (75%) the cytosolic expression of luciferase whereas at the same concentration the peptide-free propynylated ODN or the propynylated ODN-peptides containing an inactive NES were nearly inactive.

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The structure of an entire noncovalent immunoglobulin kappa light-chain dimer (Bence-Jones protein) reveals a weak and unusual constant domains association

Monoclonal free light chains secreted in immunoproliferative disorders art : frequently involved in renal complications, including a specific proximal tubule impairment, Fanconi’s syndrome. The latter is characterized in most cases by intracellular crystallization including a light-chain variable-domain fragment which resists lysosomal proteases. Bence-Jones protein (BJP) DEL was isolated from a patient with myeloma-associated Fanconi’s syndrome. The crystal structure of this human K immunoglobulin light-chain noncovalent dimer was determined using molecular replacement with the structure of molecule REI, as the variable domain, and that of BJP LOC as the constant domain.

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The sugar binding activity of MR60, a mannose-specific shuttling lectin, requires a dimeric state

MR60 is an intracellular membrane protein which has been shown to act as a mannoside specific lectin and to be identical to ERGIC-53, a protein characteristic of the endoplasmic reticulum-Golgi apparatus-intermediate compartment, acting as a shuttle. According to its primary sequence, this MR60/ERGIC-53 protein contains a luminal domain including the carbohydrate recognition domain, a stem, a transmembrane segment and a cytosolic domain. The endogenous MR60/ERGIC-53 protein is spontaneously oligomeric, (dimers and hexamers), In this paper, we study the relationship between the oligomerization state and the sugar binding capacity by using recombinant proteins.

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The Tat protein of HIV-1 induces galectin-3 expression

Animal lectins play important roles in a variety of biological processes via their recognition of glycoconjugates. Galectin-3 is a ß-galactoside-binding lectin whose expression is associated with various pathological processes including human T lymphotropic virus (HTLV)-I-infection of human T cell lines and human immunodeficiency virus (HIV) infection of T-lymphoblastic Molt-3 cell line. In the case of HIV-infected cells, it has been suggested that the increase in galectin-3 expression could be related to the expression of the viral regulatory gene tat. These results prompt us to perform more extensive analyses of the relationship between galectin-3 and HIV-1 Tat expressions. In this study, we found that Tat protein expression induces an upregulation of galectin-3 in several human cell lines. In cotransfection experiments, the 5’-regulatory sequences of the galectin-3 gene were significantly upregulated by expression vectors encoding the Tat protein. Analysis performed with 5’-regulatory deleted sequences suggested that galectin-3 induction by Tat is dependent on activation of the Sp-1 binding transcription factor.

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Theoretical study of the conformation of the H-protein lipoamide arm as a function of its terminal group

The glycine decarboxylase complex consists of four different proteins (the L-, P-, H-, and T-proteins). The H-protein plays a central role in communication among the other enzymes, as its lipoamide arm interacts successively with each of the components of the complex. The crystal structures of two states of the H-protein have been resolved : the oxidized form, H-ox at 2 Angstrom and the methylamine-loaded form, H-met at 2.2 Angstrom. However, the position of the arm for the reduced form, H-red, is still unknown. We have performed numerical free-energy calculations in order to better understand the differences in the structures and to elucidate the conformation of the arm in H-red. The results of the simulations are in agreement with the crystallographic results, as the minima of the free energy surface for H-ox and H-met correspond to the crystal structures.

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Zinc-induced conformational transitions of acidic peptides : Characterization by circular dichroism and electrospray mass spectrometry

A series of amphiphilic peptides have been synthesized which have a defined chain length and are based either on the dipeptide periodicity Asp-Leu or the tetrapeptide periodicity Leu-Asp-Asp-Leu. Their behavior in the presence of low concentrations of metal ions was studied by circular dichroism spectroscopy, In pure water, the peptides adopt a random coil conformation. The addition of Zn2+ specifically induces a beta-sheet structure for (Asp-Leu)(n) and an alpha-helix structure for (Leu-Asp-Asp-Leu)(n)-Asp. The conformational transitions are dependent on the chain length : the critical main chain length for beta-sheets and alpha-helix formation is between 10 and 24 residues, and between 13 and 25 residues, respectively. The addition of NH4+ and Mg2+ have no effect, whereas Ca2+ has only a slight effect on the conformation.

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1H-NMRD and 17O-NMR assessment of water exchange and rotational dynamics of two potential MRI agents : MP-1177 (an extracellular agent) and MP-2269 (a blood pool agent).

The parameters that govern water proton magnetic relaxation (e.g. water exchange rates, and rotational and electronic correlation times) of representatives of two classes of Gd(III) complexes have been estimated, using two different approaches and the results compared with those derived for known analogs. The complexes studied are : (i) the non-ionic GdDTPA-bis(-methoxyethyl-amide) [Gd(DTPA-BMEA)], a typical small-molecule extracellular MR agent, and (ii) the ionic Gd(III) complex of 4-pentylbicyclo[2.2.2]octane-1-carboxyl-di-L-aspartyl-lysine-deriv ed-DTPA [GdL]4-, a prototype MR blood pool agent, which binds to serum albumin in vivo through non-covalent hydrophobic interactions. An 17O-NMR study of [Gd(DTPA-BMEA)] gives a water exchange rate constant of k(ex)298 = (0.39 +/- 0.02) x 10(6) s(-1), identical to that for the bismethylamide analog [Gd(DTPA-BMA)].

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