Comparison of the photoluminescence properties of semiconductor quantum dots and non-blinking diamond nanoparticles. Observation of the diffusion of diamond nanoparticles in living cells

Long-term observations of photoluminescence at the single-molecule level were until recently very diffcult, due to the photobleaching of organic ?uorophore molecules. Although inorganic semiconductor nanocrystals can overcome this diffculty showing very low photobleaching yield, they suffer from photoblinking. A new marker has been recently introduced, relying on diamond nanoparticles containing photoluminescent color centers. In this work we compare the photoluminescence of single quantum dots (QDs) to the one of nanodiamonds containing a single-color center. Contrary to other markers, photoluminescent nanodiamonds present a perfect photostability and no photoblinking. At saturation of their excitation, nanodiamonds photoluminescence intensity is only three times smaller than the one of QDs. Moreover, the bright and stable photoluminescence of nanodiamonds allows wide field observations of single nanoparticles motion. We demonstrate the possibility of recording the tra jectory of such single particle in culture cells

Etude structurale de monocouches lipidiques par simulations de dynamique moléculaire

Les membranes biologiques jouent un rôle essentiel dans la vie cellulaire. Afin d étudier leur comportement et leurs interactions avec des molécules, des modèles de monocouches lipidiques ont été développés. Leur compression sur balance de Langmuir permet d obtenir une isotherme pression de surface-aire moléculaire permettant de caractériser notamment les transitions de phase et le comportement interfacial des monocouches. Seules les études de simulations de dynamique moléculaire permettent d obtenir les propriétés structurales des lipides organisés en monocouche à l échelle atomique. Nous avons modélisé une monocouche de 1-palmitoyl-2-oléoyl-sn-glycéro-3-phosphocholine (POPC), phospholipides majoritaires des membranes, puis réalisé une série de dynamiques moléculaires à différentes tensions de surface en utilisant GROMACS et le champ de force tout atome GAFF. Une isotherme de compression de POPC a été obtenue pour la première fois par simulation de dynamique moléculaire. L analyse structurale des POPC a mis en évidence des variations conformationelles avec l augmentation de la pression ainsi qu'une distribution bimodale de l orientation des têtes polaires. L analyse des angles dièdres a permis d identifier les torsions responsables de cette flexibilité. Un comportement indépendant des chaînes hydrophobes a été observé et corrélé à un assemblage préférentiel des chaînes oléoyle d une part et palmitoyle d autre part. La connaissance des propriétés structurales et organisationnelles des monocouches de POPC est essentielle à la caractérisation des interactions mises en jeu dans la cohésion des films lipidiques et fournit une base à l étude de leur perturbation par des molécules.Biomembranes play an essential role in many relevant processes in cellular biology. In order to gain insight into their behaviour and interactions with molecules, models such as lipid monolayers have been developed. Monolayer compression on Langmuir trough provides surface pressure molecular area isotherms, and allows characterisation of phase and interfacial properties of the monolayer. Such a characterisation can be completed by atomistic study of the monolayer phospholipids and molecular interactions from molecular dynamic simulations. Our work is focused on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), a lipid comprising a saturated and an unsaturated acyl chain, major lipids in eukaryotic cell membranes. We performed MD simulations at 293 K and 300 K at different surface pressures using the all-atom general amber force field (GAFF). Simulated surface pressure-area isotherms were obtained for the first time, and a good agreement was found with experimental isotherms. Based on the structural analyses, two orientations of the head groups clearly appear. We propose that the conformational variations around the bonds connecting the phosphorus atom to the adjacent oxygen are involved in these specific orientations. Both acyl chains have distinct structural properties upon compression and suggest an independent behavior of the saturated and unsaturated chains that could be correlated with the formation of chain-type clusters observed along the simulated trajectories. Molecular insight in structural properties of POPC monolayer provides essential clues for the study of membrane-molecule interaction.EVRY-Bib. électronique (912289901) / SudocSudocFranceF

YB-1 promotes microtubule assembly in vitro through interaction with tubulin and microtubules

<p>Abstract</p> <p>Background</p> <p>YB-1 is a major regulator of gene expression in eukaryotic cells. In addition to its role in transcription, YB-1 plays a key role in translation and stabilization of mRNAs.</p> <p>Results</p> <p>We show here that YB-1 interacts with tubulin and microtubules and stimulates microtubule assembly <it>in vitro</it>. High resolution imaging via electron and atomic force microscopy revealed that microtubules assembled in the presence of YB-1 exhibited a normal single wall ultrastructure and indicated that YB-1 most probably coats the outer microtubule wall. Furthermore, we found that YB-1 also promotes the assembly of MAPs-tubulin and subtilisin-treated tubulin. Finally, we demonstrated that tubulin interferes with RNA:YB-1 complexes.</p> <p>Conclusion</p> <p>These results suggest that YB-1 may regulate microtubule assembly <it>in vivo </it>and that its interaction with tubulin may contribute to the control of mRNA translation.</p

Polyamine Sharing between Tubulin Dimers Favours Microtubule Nucleation and Elongation via Facilitated Diffusion

We suggest for the first time that the action of multivalent cations on microtubule dynamics can result from facilitated diffusion of GTP-tubulin to the microtubule ends. Facilitated diffusion can promote microtubule assembly, because, upon encountering a growing nucleus or the microtubule wall, random GTP-tubulin sliding on their surfaces will increase the probability of association to the target sites (nucleation sites or MT ends). This is an original explanation for understanding the apparent discrepancy between the high rate of microtubule elongation and the low rate of tubulin association at the microtubule ends in the viscous cytoplasm. The mechanism of facilitated diffusion requires an attraction force between two tubulins, which can result from the sharing of multivalent counterions. Natural polyamines (putrescine, spermidine, and spermine) are present in all living cells and are potent agents to trigger tubulin self-attraction. By using an analytical model, we analyze the implication of facilitated diffusion mediated by polyamines on nucleation and elongation of microtubules. In vitro experiments using pure tubulin indicate that the promotion of microtubule assembly by polyamines is typical of facilitated diffusion. The results presented here show that polyamines can be of particular importance for the regulation of the microtubule network in vivo and provide the basis for further investigations into the effects of facilitated diffusion on cytoskeleton dynamics

Transport des Lipoproteines de Basse densite dans la paroi arterielle. Role fonctionnel des recepteurs LDL, effets de l'hyperpression arterielle

SIGLEINIST T 77408 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Mécanismes moléculaires de l'interaction entre la tubuline et les protéines de la famille de la stathmine

La stathmine est une petite phosphoprotéine ubiquiste trés conservée chez les vertébrés. Son expression est régulée au cours de la prolifération et de la différenciation cellulaire, ainsi qu' au cours de certains cancers. La stathminer est aussi l'élément générique d'une famille de protéines qui possèdent toutes un domaine de grande similitude de séquence avec la stathmine (SLD). Les divers SLD séquestrent la tubuline dans un complexe non polymérisable constitué de deux hétérodimères de tubuline par molécule de SLD (T2-SLD) mais avec des stabilités variables. Ce travail de thèse s'inscrit dans le cadre général de la description de ces interactions et de la recherche des raisons de leur diversité. J'ai ainsi tenté de modéliser ces interactions et j'ai étudié le rôle de trois sous-domaines de SLD. Ces travaux ont ..PARIS5-BU-Necker : Fermée (751152101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Procédé de marquage d'un objet par microdiamants

L'invention concerne un procédé de marquage d'un objet. Ce procédé comporte les étapes suivantes : (a) On fournit plusieurs microdiamants (10) fluorescents dont la dimension maximale de chacun est inférieure à 50 microns, (b) On répartit ces microdiamants (10) dans une région (95) de cet objet (90) à des positions, (c) On fixe ces microdiamants dans cette région (95)

Rapid Assembly and Collective Behavior of Microtubule Bundles in the Presence of Polyamines

International audienceMicrotubules (MTs) are cylindrical cytoskeleton polymers composed of α-β tubulin heterodimers whose dynamic properties are essential to fulfill their numerous cellular functions. In response to spatial confinement, dynamic MTs, even in the absence of protein partners, were shown to self-organize into higher order structures (spindle or striped structures) which lead to interesting dynamical properties (MT oscillations). In this study, we considered the assembly and sensitivity of dynamic MTs when in bundles. To perform this study, spermine, a natural tetravalent polyamine present at high concentrations in all eukaryote cells, was used to trigger MT bundling while preserving MT dynamics. Interestingly, we first show that, near physiological ionic strengths, spermine promotes the bundling of MTs whereas it does not lead to aggregation of free tubulin, which would have been detrimental to MT polymerization. Experimental and theoretical results also indicate that, to obtain a high rate of bundle assembly, bundling should take place at the beginning of assembly when rapid rotational movements of short and newly nucleated MTs are still possible. On the other hand, the bundling process is significantly slowed down for long MTs. Finally, we found that short MT bundles exhibit a higher sensitivity to cold exposure than do isolated MTs. To account for this phenomenon, we suggest that a collective behavior takes place within MT bundles because an MT entering into a phase of shortening could increase the probability of the other MTs in the same bundle to enter into shortening phase due to their close proximity. We then elaborate on some putative applications of our findings to in vivo conditions including neurons

NMR Solution Structure of Neurotensin in Membrane-Mimetic Environments: Molecular Basis for Neurotensin Receptor Recognition ‡

International audienceNeurotensin (NT) is a 13-residue neuropeptide that exerts multiple biological functions in thecentral and peripheral nervous system. Little is known about the structure of this neuropeptide, and whatis known only concerns its C-terminal part. We determined here for the first time the structure of thefull-length NT in membrane-mimicking environments by means of classical proton-proton distanceconstraints derived from solution-state NMR spectroscopy. NT was found to have a structure at both itsN and C termini, whereas the central region of NT remains highly flexible. In TFE and HFIP solutions,the NT C-terminus presents an extended slightly incurved structure, whereas in DPC it has a‚turn. TheN-terminal region of NT possesses great adaptability and accessibility to the microenvironment in thethree media studied. Altogether, our work demonstrates a structure of NT fully compatible with its NTR-bound state