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[en] The aim of this work is to study the complexation of actinides by amino acids in one hand and in another hand, by transferrin. This work presents the first results obtained with the cations Np(IV) and Th(IV). The actinides chelation by transferrin has been revealed by UV-Visible and infrared spectroscopies. The determination of the structure of the complexation site has been studied by X rays absorption spectroscopy. Nevertheless, the complexity of the structure of the transferrin chelation site makes the analysis of the EXAFS spectra difficult. The study of the interaction between each amino acid present in the chelation site and the actinide cation would allow to better interpret the X absorption spectra. Thus, a study on penta-peptides miming a part of the iron site of the transferrin is required too to better understand the interaction processes between the actinide ion and the amino acids of this site. Among these last ones, the aspartate (carboxylate function) can be represented by the acetate ligand. Moreover, the penta-peptide (Asp-Asp-Pro-Asp-Asp with Asp: aspartate and Pro: proline), which has been synthesized, seems to be a good model of chelating agent for a part of the iron site. These two ligands have been used for complexing Np(IV). The spectroscopic and structural data relative to these complexes have been qualitatively compared to the data obtained on the system Np(IV)-Tf and Th(IV)-Tf (Tf: transferrin). A first analysis of these EXAFS spectra seems to confirm the complexation of the Np(IV) to transferrin as, in the same experimental conditions, Th(IV) could be not chelated. (O.M.)
[en] Pairing of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins on vesicles (v-SNAREs) and SNARE proteins on target membranes (t-SNAREs) mediates intracellular membrane fusion. VAMP3/cellubrevin is a v-SNARE that resides in recycling endosomes and endosome-derived transport vesicles. VAMP3 has been implicated in recycling of transferrin receptors, secretion of α-granules in platelets, and membrane trafficking during cell migration. Using a cell fusion assay, we examined membrane fusion capacity of the ternary complexes formed by VAMP3 and plasma membrane t-SNAREs syntaxin1, syntaxin4, SNAP-23 and SNAP-25. VAMP3 forms fusogenic pairing with t-SNARE complexes syntaxin1/SNAP-25, syntaxin1/SNAP-23 and syntaxin4/SNAP-25, but not with syntaxin4/SNAP-23. Deletion of the N-terminal domain of syntaxin4 enhanced membrane fusion more than two fold, indicating that the N-terminal domain negatively regulates membrane fusion. Differential membrane fusion capacities of the ternary v-/t-SNARE complexes suggest that transport vesicles containing VAMP3 have distinct membrane fusion kinetics with domains of the plasma membrane that present different t-SNARE proteins
[en] Molecular interactions control the distribution of radionuclides and their mechanisms of action. They explain most of their toxicological properties in addition to ionizing properties. The study of uranyl interactions with a large variety of proteins displays a rich physico-chemistry of which the complexity has to be considered when elaborating biokinetic models or when designing novel de-corporating molecules. (author)
[en] Highlights: • Analytical procedures for estimation of iron/transferrin parameters has been proposed under flow analysis conditions. • MCFA system for serum iron and unsaturated iron binding capacity determination has been developed. • Two different analytical approaches for determination of each parameter have been proposed. • The proposed MCFA system is useful for analysis of human serum samples. - Abstract: The Multicommutated Flow Analysis (MCFA) system for the estimation of clinical iron parameters: Serum Iron (SI), Unsaturated Iron Binding Capacity (UIBC) and Total Iron Binding Capacity (TIBC) has been proposed. The developed MCFA system based on simple photometric detection of iron with chromogenic agent (ferrozine) enables a speciation of transferrin (determination of free and Fe-bound protein) in human serum. The construction of manifold was adapted to the requirements of measurements under changing conditions. In the course of studies, a different effect of proteins on SI and UIBC determination has been proven. That was in turn the reason to perform two kinds of calibration methods. For measurements in acidic medium for SI/holotransferrin determination, the calibration curve method was applied, characterized by limit of determination and limit of quantitation on the level of 3.4 μmol L−1 and 9.1 μmol L−1, respectively. The determination method for UIBC parameter (related to apotransferrin level) in physiological medium of pH 7.4 forced the use of standard addition method due to the strong influence of proteins on obtaining analytical signals. These two different methodologies, performed in the presented system, enabled the estimation of all three clinical iron/transferrin parameters in human serum samples. TIBC corresponding to total transferrin level was calculated as a sum of SI and UIBC.
[en] For toxicological purposes, general understanding needs to be deepened on intramolecular interactions in molecular actinide species. Metallo-biomolecules are thus considered as elaborate inorganic complexes with well-designed metal active sites. Although the various interaction processes between essential biological cations and proteins are widely studied, focus on the actinides is more seldom. Because of its major role on iron transport, our study focuses on the transferrin system. To cast light on the interaction between transferrin and actinides, this paper presents a brief review of related data in the literature. In this field, X ray Absorption Spectroscopy can be used as a structural and electronic metal cation probe. Combination with more traditional spectroscopic techniques such as spectrophotometry is ideal for the understanding of the chelation mechanism. Our recent results on holotransferrin are presented at the end of the paper. Fitting of the EXAFS data needs to take into account multiple scattering effects. The first low-Z (oxygen and/or nitrogen atoms) co-ordination shell has been found at 2.02 angstrom, in good agreement with literature structural data obtained with X-ray diffraction. Parallelly, study of actinide complexation with transferrin has been undertaken with UV-vis-NIR spectroscopy and EXAFS. (authors)