Articles

Sub-picosecond Raman spectrometer for time-resolved studies of structural dynamics in heme proteins
- Kruglik Sergei G.
- Lambry Jean-Christophe
- Martin Jean-Louis
- Vos Marten H.
- Négrerie Michel
Journal of Raman Spectroscopy, Wiley , 2011, 42 (3), pp.265 . We describe a pump-probe Raman spectrometer based on a femtosecond Ti:sapphire laser, an optical parametric generator and two optical parametric amplifiers for time-resolved studies, with emphasis on the structural dynamics in heme proteins. The system provides a 100-fs pump pulse tunable in the range 500-600 nm and a transform-limited sub-picosecond probe pulse tunable in the range 390-450 nm. The spectrometer has spectral (25 cm(-1)) and temporal (similar to 0.7 ps) resolutions which constitute an effective compromise for identifying transient heme protein species and for following their structural evolution by spontaneous Raman scattering in the time range 0.5 ps to 2 ns. This apparatus was applied to time-resolved studies of a broad range of heme proteins, monitoring the primary dynamics of photoinduced heme coordination state and structural changes, its interaction with protein side-chains and diatomic gaseous ligands, as well as heme vibrational cooling. The treatment of transient Raman spectra is described in detail, and the advantages and shortcomings of spontaneous resonance Raman spectroscopy for ultrafast heme proteins studies are discussed. We demonstrate the efficiency of the constructed spectrometer by measuring Raman spectra in the sub-picosecond and picosecond time ranges for the oxygen-storage heme protein myoglobin and for the oxygen-sensor heme protein FixLH in interaction with the diatomic gaseous ligands CO, NO, and O-2. Copyright (C) 2010 John Wiley and Sons, Ltd. (10.1002/jrs.2685)
DOI : 10.1002/jrs.2685
Deep and fast live imaging with two-photon scanned light-sheet microscopy
- Truong T.V.
- Supatto Willy
- Koos D.S.
- Choi J.M.
- Fraser S.E.
Nature Methods, Nature Publishing Group , 2011, 8 (9), pp.757 . We implemented two-photon scanned light-sheet microscopy, combining nonlinear excitation with orthogonal illumination of light-sheet microscopy, and showed its excellent performance for in vivo, cellular-resolution, three-dimensional imaging of large biological samples. Live imaging of fruit fly and zebrafish embryos confirmed that the technique can be used to image up to twice deeper than with one-photon light-sheet microscopy and more than ten times faster than with point-scanning two-photon microscopy without compromising normal biology. Cop. 2011 Nature America, Inc. All rights reserved. (10.1038/nmeth.1652)
DOI : 10.1038/nmeth.1652
Dynamics of NO interacting with soluble guanylate cyclase from 1 ps to 0.1 s and induced structural transitions
- Yoo Byung-Kuk
- Lamarre Isabelle
- Martin Jean-Louis
- Rappaport Fabrice
- Negrerie Michel
BMC Pharmacology, BioMed Central , 2011, 11 (Suppl 1), pp.P77 .
Combining rails and anchors with laser forcing for selective manipulation within 2D droplet arrays.
- Fradet Etienne
- Mcdougall Craig
- Abbyad Paul
- Dangla Rémi
- Mcgloin David
- Baroud Charles N.
Lab on a Chip, Royal Society of Chemistry , 2011, 11 (24), pp.4228-4234 . We demonstrate the combination of a rails and anchors microfluidic system with laser forcing to enable the creation of highly controllable 2D droplet arrays. Water droplets residing in an oil phase can be pinned to anchor holes made in the base of a microfluidic channel, enabling the creation of arrays by the appropriate patterning of such holes. The introduction of laser forcing, via laser induced thermocapillary forces to anchored droplets, enables the selective extraction of particular droplets from an array. We also demonstrate that such anchor arrays can be filled with multiple, in our case two, droplets each and that if such droplets have different chemical contents, the application of a laser at their interface triggers their merging and a chemical reaction to take place. Finally by adding guiding rails within the microfluidic structure we can selectively fill large scale arrays with monodisperse droplets with significant control over their contents. In this way we make a droplet array filled with 96 droplets containing different concentrations of fluorescent microparticles. (10.1039/C1LC20541B)
DOI : 10.1039/C1LC20541B
Vibrational Motions Associated with Primary Processes in Bacteriorhodopsin Studied by Coherent Infrared Emission Spectroscopy
- Groma Geza I.
- Colonna Anne
- Martin Jean-Louis
- Vos Marten H.
Biophysical Journal, Biophysical Society , 2011, 100 (6), pp.1578 . The primary energetic processes driving the functional proton pump of bacteriorhodopsin take place in the form of complex molecular dynamic events after excitation of the retinal chromophore into the Franck-Condon state. These early events include a strong electronic polarization, skeletal stretching, and all-trans-to-13-cis isomerization upon formation of the J intermediate. The effectiveness of the photoreaction is ensured by a conical intersection between the electronic excited and ground states, providing highly nonadiabatic coupling to nuclear motions. Here, we study real-time vibrational coherences associated with these motions by analyzing light-induced infrared emission from oriented purple membranes in the 750-1400 cm(-1) region. The experimental technique applied is based on second-order femtosecond difference frequency generation on macroscopically ordered samples that also yield information on phase and direction of the underlying motions. Concerted use of several analysis methods resulted in the isolation and characterization of seven different vibrational modes assigned as C-C stretches, out-of-plane methyl rocks, and hydrogen out-of-plane wags, whereas no in-plane H rock was found. Based on their lifetimes and several other criteria, we deduce that the majority of the observed modes take place on the potential energy surface of the excited electronic state. In particular, the direction sensitivity provides experimental evidence for large intermediate distortions of the retinal plane during the excited-state isomerization process. (10.1016/j.bpj.2011.02.011)
DOI : 10.1016/j.bpj.2011.02.011
Strong Ligand-Protein Interactions Revealed by Ultrafast Infrared Spectroscopy of CO in the Heme Pocket of the Oxygen Sensor FixL
- Nuernberger Patrick
- Lee Kevin F.
- Bonvalet Adeline
- Bouzhir-Sima Latifa
- Lambry Jean-Christophe
- Liebl Ursula
- Joffre Manuel
- Vos Marten H.
Journal of the American Chemical Society, American Chemical Society , 2011, 133 (43), pp.17110 . In heme-based sensor proteins, ligand binding to heme in a sensor domain induces conformational changes that eventually lead to changes in enzymatic activity of an associated catalytic domain. The bacterial oxygen sensor FixL is the best-studied example of these proteins and displays marked differences in dynamic behavior with respect to model globin proteins. We report a mid-IR study of the configuration and ultrafast dynamics of CO in the distal heme pocket site of the sensor PAS domain FixLH, employing a recently developed method that provides a unique combination of high spectral resolution and range and high sensitivity. Anisotropy measurements indicate that CO rotates toward the heme plane upon dissociation, as is the case in globins. Remarkably, CO bound to the heme iron is tilted by similar to 30 degrees with respect to the heme normal, which contrasts to the situation in myoglobin and in present FixLH-CO X-ray crystal structure models. This implies protein-environment-induced strain on the ligand, which is possibly at the origin of a very rapid docking-site population in a single conformation. Our observations likely explain the unusually low affinity of FixL for CO that is at the origin of the weak ligand discrimination between CO and O(2). Moreover, we observe orders of magnitude faster vibrational relaxation of dissociated CO in FixL than in globins, implying strong interactions of the ligand with the distal heme pocket environment. Finally, in the R220H FixLH mutant protein, where CO is H-bonded to a distal histidine, we demonstrate that the H-bond is maintained during photolysis. Comparison with extensively studied globin proteins unveils a surprisingly rich variety in both structural and dynamic properties of the interaction of a diatomic ligand with the ubiquitous b-type heme-proximal histidine system in different distal pockets. (10.1021/ja204549n)
DOI : 10.1021/ja204549n
Measurement of circular dichroism dynamics in a nanosecond temperature-jump experiment
- Khuc Mai-Thu
- Mendonça Lucille
- Sharma S.
- Volk M.
- Solinas Xavier
- Hache François
Review of Scientific Instruments, American Institute of Physics , 2011, 82 (5) . The use of a fast temperature jump (T-jump) is a very powerful experiment aiming at studying protein denaturation dynamics. However, probing the secondary structure is a difficult challenge and rarely yields quantitative values. We present the technical implementation of far-UV circular dichroism in a nanosecond T-jump experiment and show that this experiment allows us to follow quantitatively the change in the helical fraction of a poly(glutamic acid) peptide during its thermal denaturation with 12 ns time resolution. Cop. 2011 American Institute of Physics. (10.1063/1.3592331)
DOI : 10.1063/1.3592331
The archaeal Xpf/Mus81/FANCM homolog Hef and the Holliday junction resolvase Hjc define alternative pathways that are essential for cell viability in Haloferax volcanii
- Lestini Roxane
- Allers Thorsten
DNA Repair, Elsevier , 2010, 9 (9), pp.994-1002 . (10.1016/j.dnarep.2010.06.012)
DOI : 10.1016/j.dnarep.2010.06.012
Multiphoton microscopy of engineered dermal substitutes: assessment of 3-D collagen matrix remodeling induced by fibroblast contraction.
- Pena Ana-Maria
- Fagot Dominique
- Olive Christian
- Michelet Jean-François
- Galey Jean-Baptiste
- Leroy Frédéric
- Beaurepaire Emmanuel
- Martin Jean-Louis
- Colonna Anne
- Schanne-Klein Marie-Claire
Journal of Biomedical Optics, Society of Photo-optical Instrumentation Engineers , 2010, 15 (5) . Dermal fibroblasts are responsible for the generation of mechanical forces within their surrounding extracellular matrix and can be potentially targeted by anti-aging ingredients. Investigation of the modulation of fibroblast contraction by these ingredients requires the implementation of three-dimensional in situ imaging methodologies. We use multiphoton microscopy to visualize unstained engineered dermal tissue by combining second-harmonic generation that reveals specifically fibrillar collagen and two-photon excited fluorescence from endogenous cellular chromophores. We study the fibroblast-induced reorganization of the collagen matrix and quantitatively evaluate the effect of Y-27632, a RhoA-kinase inhibitor, on dermal substitute contraction. We observe that collagen fibrils rearrange around fibroblasts with increasing density in control samples, whereas collagen fibrils show no remodeling in the samples containing the RhoA-kinase inhibitor. Moreover, we show that the inhibitory effects are reversible. Our study demonstrates the relevance of multiphoton microscopy to visualize three-dimensional remodeling of the extracellular matrix induced by fibroblast contraction or other processes. (10.1117/1.3503411)
DOI : 10.1117/1.3503411
Cell lineage reconstruction of early zebrafish embryos using label-free nonlinear microscopy
- Olivier Nicolas
- Luengo-Oroz Miguel Angel
- Duloquin Louise
- Faure Emmanuel
- Savy Thierry
- Veilleux Israël
- Solinas Xavier
- Débarre Delphine
- Bourgine Paul
- Santos Andrés
- Peyriéras Nadine
- Beaurepaire Emmanuel
Science, American Association for the Advancement of Science (AAAS) , 2010, 329 (5994), pp.967-71 . Quantifying cell behaviors in animal early embryogenesis remains a challenging issue requiring in toto imaging and automated image analysis. We designed a framework for imaging and reconstructing unstained whole zebrafish embryos for their first 10 cell division cycles and report measurements along the cell lineage with micrometer spatial resolution and minute temporal accuracy. Point-scanning multiphoton excitation optimized to preferentially probe the innermost regions of the embryo provided intrinsic signals highlighting all mitotic spindles and cell boundaries. Automated image analysis revealed the phenomenology of cell proliferation. Blastomeres continuously drift out of synchrony. After the 32-cell stage, the cell cycle lengthens according to cell radial position, leading to apparent division waves. Progressive amplification of this process is the rule, contrasting with classical descriptions of abrupt changes in the system dynamics. (10.1126/science.1189428)
DOI : 10.1126/science.1189428
RNA polymerase mutations that facilitate replication progression in the rep uvrD recF mutant lacking two accessory replicative helicases
- Baharoglu Zeynep
- Lestini Roxane
- Duigou Stéphane
- Michel Bénédicte
Molecular Microbiology, Wiley , 2010, 77 (2), pp.324 . We observed that cells lacking Rep and UvrD, two replication accessory helicases, and the recombination protein RecF are cryo-sensitive on rich medium. We isolated five mutations that suppress this LB-cryo-sensitivity and show that they map in the genes encoding the RNA polymerase subunits RpoB and RpoC. These rpoB (D444G, H447R and N518D) and rpoC mutants (H113R and P451L) were characterized. rpoBH447R and rpoBD444G prevent activation of the Prrn core promoter in rich medium, but only rpoBH447R also suppresses the auxotrophy of a relA spoT mutant (stringent-like phenotype). rpoCH113R suppresses the thermo-sensitivity of a greA greB mutant, suggesting that it destabilizes stalled elongation complexes. All mutations but rpoCP451L prevent R-loop formation. We propose that these rpo mutations allow replication in the absence of Rep and UvrD by destabilizing RNA Pol upon replication-transcription collisions. In a RecF+ context, they improve growth of rep uvrD cells only if DinG is present, supporting the hypothesis that Rep, UvrD and DinG facilitate progression of the replication fork across transcribed sequences. They rescue rep uvrD dinG recF cells, indicating that in a recF mutant replication forks arrested by unstable transcription complexes can restart without any of the three known replication accessory helicases Rep, UvrD and DinG. (10.1111/j.1365-2958.2010.07208.x)
DOI : 10.1111/j.1365-2958.2010.07208.x
Harmonic microscopy of isotropic and anisotropic microstructure of the human cornea
- Olivier Nicolas
- Aptel Florent
- Plamann Karsten
- Schanne-Klein Marie-Claire
- Beaurepaire Emmanuel
Optics Express, Optical Society of America - OSA Publishing , 2010, 18 (5), pp.5028-5040 . In this study we present combined third-harmonic generation (THG) and second-harmonic generation (SHG) microscopy images of intact human corneas, and we analyze experimentally and theoretically the origin of the THG signal. Multiharmonic microscopy provides detailed images of the cornea microstructure over its entire thickness. A component of the THG signal originates from cellular structures and another one originates from anisotropy changes between successive collagen lamellae in the stroma. This anisotropy-related signal can be specifically detected using circular incident polarization, and provide contrasted images of the stacking and tissue-scale heterogeneity of stromal lamellae. Forward-radiated THG and SHG signals are generally anticorrelated, indicating that maximum THG is obtained from lamellar interfaces whereas maximum SHG is obtained from within lamellae. Polarization-resolved THG imaging reflects the a ernate anisotropy directions of the lamellae. We present a model for THG imaging of layered anisotropic samples and numerical calculations that account for our observations. (10.1364/OE.18.005028)
DOI : 10.1364/OE.18.005028
Nonlinear optical imaging of lyotropic cholesteric liquid crystals.
- Deniset-Besseau Ariane
- de Sa Peixoto Paolo
- Mosser G.
- Schanne-Klein Marie-Claire
Optics Express, Optical Society of America - OSA Publishing , 2010, 18 (2), pp.1113-1121 . We use nonlinear optical microscopy combining Second Harmonic Generation (SHG) microscopy and Two-Photon Excited Fluorescence (2PEF) signals to characterize collagen lyotropic liquid crystals. We show that SHG signals provide highly contrasted images of the three-dimensional texture of cholesteric patterns with submicrometer lateral resolution. Moreover, simultaneous recording of the 2PEF signal enables in situ quantitative mapping of the molecular concentration and its correlation with the observed textures. We apply this technique to the characterization of biomimetic textures obtained in concentrated collagen liquid solutions. We successfully image biologically relevant organizations that are similar to the collagen organization found as a stabilized state in compact bones. (10.1364/OE.18.001113)
DOI : 10.1364/OE.18.001113
Multimodal Nonlinear Imaging of the Human Cornea
- Aptel Florent
- Olivier Nicolas
- Deniset-Besseau Ariane
- Legeais Jean-Marc
- Plamann Karsten
- Schanne-Klein Marie-Claire
- Beaurepaire Emmanuel
Investigative Ophthalmology & Visual Science, Association for Research in Vision and Ophthalmology , 2010, 51 (5), pp.2459-2465 . Purpose: to evaluate the potential of third-harmonic generation (THG) microscopy combined with second-harmonic generation (SHG) and two-photon excited fluorescence (2PEF) microscopies for visualizing the microstructure of the human cornea and trabecular meshwork based on their intrinsic nonlinear properties. Methods: fresh human corneal buttons and corneoscleral discs from an eye bank were observed under a multiphoton microscope incorporating a titanium-sapphire laser and an optical parametric oscillator for the excitation, and equipped with detection channels in the forward and backward directions. Results: original contrast mechanisms of THG signals in cornea with physiological relevance were elucidated. THG microscopy with circular incident polarization detected microscopic anisotropy and revealed the stacking and distribution of stromal collagen lamellae. THG imaging with linear incident polarization also revealed cellular and anchoring structures with micrometer resolution. In edematous tissue, a strong THG signal around cells indicated the local presence of water. Additionally, SHG signals reflected the distribution of fibrillar collagen, and 2PEF imaging revealed the elastic component of the trabecular meshwork and the fluorescence of metabolically active cells. Conclusions: the combined imaging modalities of THG, SHG, and 2PEF provide key information about the physiological state and microstructure of the anterior segment over its entire thickness with remarkable contrast and specificity. This imaging method should prove particularly useful for assessing glaucoma and corneal physiopathologies. (10.1167/iovs.09-4586)
DOI : 10.1167/iovs.09-4586
Ultrafast conformational dynamics in molecules and biomolecules studied by time-resolved circular dichroism
- Hache François
Nonlinear optics, quantum optics, Old City Pub. , 2010, 40 (1-4), pp.287 . Implementation of circular dichroism in a pump-probe experiment is proposed to address the problem of ultrafast conformational changes in molecules and biomolecules. Two techniques are depicted. The first one relies on the modulation of the probe polarization and the second one uses a Babinet-Soleil compensator to analyze the changes in probe ellipticity. This technique is applied to the dynamics of the dihedral angle in photoexcited binaphthol and to the changes in conformation following photolysis of carboxy-myoglobin. Cop. 2010 Old City Publishing, Inc.
Novel approaches for targeting thymidylate synthase to overcome the resistance and toxicity of anticancer drugs
- Garg Divita
- Henrich Stefan
- Salo-Ahen Outi M. H.
- Myllykallio Hannu
- Costi Maria P.
- Wade Rebecca C.
Journal of Medicinal Chemistry, American Chemical Society , 2010, 53 (18), pp.6539-6549 . (10.1021/jm901869w)
DOI : 10.1021/jm901869w
A mechanism for the polarity formation of chemoreceptors at the growth cone membrane for gradient amplification during directional sensing
- Bouzigues Cédric
- Holcman D.
- Dahan Maxime
PLoS ONE, Public Library of Science , 2010, 5 (2) . Accurate response to external directional signals is essential for many physiological functions such as chemotaxis or axonal guidance. It relies on the detection and amplification of gradients of chemical cues, which, in eukaryotic cells, involves the asymmetric relocalization of signaling molecules. How molecular events coordinate to induce a polarity at the cell level remains however poorly understood, particularly for nerve chemotaxis. Here, we propose a model, inspired by single-molecule experiments, for the membrane dynamics of GABA chemoreceptors in nerve growth cones (GCs) during directional sensing. In our model, transient interactions between the receptors and the microtubules, coupled to GABA-induced signaling, provide a positive-feedback loop that leads to redistribution of the receptors towards the gradient source. Using numerical simulations with parameters derived from experiments, we find that the kinetics of polarization and the steady-state polarized distribution of GABA receptors are in remarkable agreement with experimental observations. Furthermore, we make predictions on the properties of the GC seen as a sensing, amplification and filtering module. In particular, the growth cone acts as a low-pass filter with a time constant -10 minutes determined by the Brownian diffusion of chemoreceptors in the membrane. This filtering makes the gradient amplification resistent to rapid fluctuations of the external signals, a beneficial feature to enhance the accuracy of neuronal wiring. Since the model is based on minimal assumptions on the receptor/cytoskeleton interactions, its validity extends to polarity formation beyond the case of GABA gradient sensing. Altogether, it constitutes an original positive-feedback mechanism by which cells can dynamically adapt their internal organization to external signals. Cop. 2010 Bouzigues et al. (10.1371/journal.pone.0009243)
DOI : 10.1371/journal.pone.0009243
Expression in E. coli and characterization of the catalytic domain of Botrytis cinerea chitin synthase.
- Magellan Hervé
- Drujon Thierry
- Thellend Annie
- Piffeteau Annie
- Becker Hubert F.
BMC Research Notes, BioMed Central , 2010, 3 (1), pp.299 . BACKGROUND: Chitin synthase 3a (CHS3a) from Botrytis cinerea (Bc) catalyses the multiple transfer of N-acetylglucosamine (GlcNAc) residues to the growing chitin chain. Chitin, a β-1,4 linked GlcNAc homopolymer, is an essential cell wall component of filamentous fungi. Chitin synthase, processive membranous protein, has been recognized as a promising target for new antifungicides. Enzymatic characterizations of chitin synthases have been limited, mainly because purity and amounts of integral enzyme obtained after purification procedures have not been sufficient. FINDINGS: We undertook the preparation of two BcCHS3a fragment proteins, containing only the central domain and devoid of the N-terminal and transmembrane C-terminal regions. The central domain of CHS3a, named SGC (Spsa GntI Core), is conserved in all UDP-glycosyltransferases and it is believed to contain the active site of the enzyme. CHS3a-SGC protein was totally expressed as inclusion bodies in Escherichia coli. We performed recombinant CHS3a-SGC purification in denaturing conditions, followed by a refolding step. Although circular dichroism spectra clearly exhibited secondary structures of renatured CHS3a-SGC, no chitin synthase activity was detected. Nevertheless CHS3a-SGC proteins show specific binding for the substrate UDP-GlcNAc with a dissociation constant similar to the Michaelis constant and a major contribution of the uracil moiety for recognition was confirmed. CONCLUSIONS: Milligram-scale quantities of CHS3a-SGC protein with native-like properties such as specific substrate UDP-GlcNAc binding could be easily obtained. These results are encouraging for subsequent heterologous expression of full-length CHS3a. (10.1186/1756-0500-3-299)
DOI : 10.1186/1756-0500-3-299
Dispersion-based pulse shaping for multiplexed two-photon fluorescence microscopy
- Labroille Guillaume
- Pillai Rajesh
- Solinas Xavier
- Boudoux Caroline
- Olivier Nicolas
- Beaurepaire Emmanuel
- Joffre Manuel
Optics Letters, Optical Society of America - OSA Publishing , 2010, 35 (20), pp.3444 . We demonstrate selective two-photon excited fluorescence microscopy with shaped pulses produced with a simple yet efficient scheme based on dispersive optical components. The pulse train from a broadband oscillator is split into two subtrains that are sent through different amounts of glass. Beam recombination results in pulse-shape switching at a rate of 150 MHz. Time-resolved photon counting detection then provides two simultaneous images resulting from selective two-photon excitation, as demonstrated in a live embryo. Although less versatile than programmable pulse-shaping devices, this novel arrangement significantly improves the performance of selective microscopy using broadband shaped pulses while simplifying the experimental setup. Cop. 2010 Optical Society of America. (10.1364/OL.35.003444)
DOI : 10.1364/OL.35.003444
Direct mid-infrared femtosecond pulse shaping with a calomel acousto-optic programmable dispersive filter
- Maksimenka Raman
- Nuernberger Patrick
- Lee Kevin F.
- Bonvalet Adeline
- Milkiewicz Jadwiga
- Barta Cestmir
- Klima Milos
- Oksenhendler Thomas
- Tournois Pierre
- Kaplan Daniel
- Joffre Manuel
Optics Letters, Optical Society of America - OSA Publishing , 2010, 35 (21), pp.3565 . Direct amplitude and phase shaping of mid-infrared femtosecond pulses is realized with a calomel-based acousto-optic programmable dispersive filter transparent between 0.4 and 20 mu m. The shaped pulse electric field is fully characterized with high accuracy, using chirped-pulse upconversion and time-encoded arrangement spectral phase interferometry for direct electric field reconstruction techniques. Complex mid-infrared pulse shapes at a center wavelength of 4: 9 mu m are generated with a spectral resolution of 14 cm(-1), which exceeds by a factor of 5 the reported experimental resolutions of calomel-based filters. Cop 2010 Optical Society of America (10.1364/OL.35.003565)
DOI : 10.1364/OL.35.003565
Quantum calculation of the second-order hyperpolarizability of chiral molecules in the "one-electron" model
- Hache François
Journal of Physical Chemistry A, American Chemical Society , 2010, 114 (37), pp.10277-10286 . Quantum calculation of the hyperpolarizabilty tensor is carried out for chiral molecules displaying a "one-electron" chirality. Calculation is made possible by introducing a chiral perturbation term in the potential energy surface. We show that a one-electron chiral molecule is intrinsically nonlinear and diplays a nonzero electric chiral hyperpolarizability. Existence of magnetic contributions is discussed, and it is shown that higherorder perturbation terms are necessary to introduce such magnetic effects in the second-order hyperpolarizability. Cop. 2010 American Chemical Society. (10.1021/jp105123m)
DOI : 10.1021/jp105123m
A thermodynamic limit of the melting/freezing processes of water under strongly hydrophobic nanoscopic confinement
- Deschamps Johnny
- Audonnet Fabrice
- Brodie-Linder Nancy
- Schoeffel Markus
- Alba-Simionesco Christiane
Physical Chemistry Chemical Physics, Royal Society of Chemistry , 2010, 12 (7), pp.1440 . We studied liquid water confined within nanopores which present a high level of hydrophobicity thanks to a new method of synthesis. We found that the liquid state persists down to temperatures much lower than in the bulk and in hydrophilic materials of comparable sizes, allowing us to define a thermo- dynamic limit for the melting/crystallization of water (10.1039/b920816j)
DOI : 10.1039/b920816j
Selective probing of a NADPH site controlled light-induced enzymatic catalysis
- Lambry Jean-Christophe
- Beaumont Edward
- Tarus Bogdan
- Blanchard-Desce Mireille
- Slama-Schwok Anny
Journal of Molecular Recognition, Wiley , 2010, 23 (4), pp.379 . Achieving molecular recognition of NADPH binding sites is a compelling strategy to control many redox biological processes. The NADPH sites recognize the ubiquitous NADPH cofactor via highly conserved binding interactions, despite differences in the regulation of the hydride transfer in redox active proteins. We recently developed a photoactive NADPH substitute, called nanotrigger NT synchronizing the initiation of enzymatic catalysis of the endothelial NO-synthase (eNOS) with a laser pulse. Spatial and temporal control of enzymatic activity by such a designed light-driven activator would benefit from achieving molecular selectivity, i.e. activation of a single NADPH-mediated enzyme. In this work, we probe the ability of NT to discriminate between two NADPH sites with light. The selected NADPH sites belong to dihydrofolate reductase dihydrofolate reductase enzyme (DHFR) and endothelial NO-synthase (eNOS). Ultrafast kinetics showed that NT could not activate DHFR catalysis with a laser pulse in contrast with the observed trigger of eNOS catalysis leading to NO formation. Homology modelling, molecular dynamics simulations showed that NT discriminated between the two NADPH sites by different donor to acceptor distances and by local steric effects hindering light activation of DHFR catalysis. The data suggested that the narrow NADPH site required a tight fit of the nanotrigger at a suitable distance/angle to the electron acceptor for a specific activation of the catalysis. The ability of the nanotrigger to activate eNOS combined with a low reactivity in unfavourable NADPH sites makes NT a highly promising tool for targeting eNOS in endothelial cells with a laser pulse. Cop 2009 John Wiley and Sons, Ltd. (10.1002/jmr.1009)
DOI : 10.1002/jmr.1009
Beam waist measurement for terahertz time-domain spectroscopy experiments
- Podzorov Alexander
- Wojdyla Antoine
- Gallot Guilhem
Optics Letters, Optical Society of America - OSA Publishing , 2010, 35 (7), pp.901 . Classical masking aperture methods are found to be mostly inaccurate to determine the terahertz beam size in terahertz time-domain spectroscopy (TDS) experiments, owing to complex diffraction effects. Here, we present a simple and reliable method for measuring beam waists in terahertz TDS. It is based on the suecessive diffraction by an opaque disk followed by a small circular aperture. Cop. 2010 Optical Society of America. (10.1364/OL.35.000901)
DOI : 10.1364/OL.35.000901
Quantifying Biomolecule Diffusivity Using an Optimal Bayesian Method
- Voisinne Guillaume
- Alexandrou Antigoni
- Masson Jean-Baptiste
Biophysical Journal, Biophysical Society , 2010, 98 (4), pp.596-605 . We propose a Bayesian method to extract the diffusivity of biomolecules evolving freely or inside membrane microdomains This approach assumes a model of motion for the paticle considered, namely free Brownian motion or confined diffusion In each framework, a systematic Bayesian scheme is provided for estimating the diffusivity We show that this method reaches the best performances theoretically achievable Its efficiency overcomes that of widely used methods based on the analysis of the mean-square displacement The approach presented here also gives direct access to the uncertainty on the estimation of the diffusivity and predicts the number of steps of the trajectory necessary to achieve any desired precision Its robustness with respect to noise on the position of the biomolecule is also investigated (10.1016/j.bpj.2009.10.051)
DOI : 10.1016/j.bpj.2009.10.051