Articles

Functionality of nitrated acetylcholine receptor: The two-step formation of nitrotyrosines reveals their differential role in effectors binding
- Négrerie Michel
- Martin Jean-Louis
- Nghiêm H.-O.
FEBS Letters, Wiley , 2005, 579 (12), pp.2643 . The presence of nitrotyrosines is associated with several neurodegenerative pathologies. We evaluated the functionality of the nicotinic acetylcholine receptor possessing nitrotyrosines. The spectrum of the nitrated receptor displays an absorption band characteristic of ortho-nitrophenol. The presence of carbamylcholine in the agonist site prevented the effect of nitration by tetranitromethane in some conditions. The nitration occurred with two discrete steps and pointed out the differential involvement of tyrosines in the binding of acetylcholine and neurotoxin. We concluded that at least two residues involved in agonist binding can be nitrated, which bring similar contributions to the binding energy of the neurotransmitter. Cop. 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved. (10.1016/j.febslet.2005.03.084)
DOI : 10.1016/j.febslet.2005.03.084
Détection des ciguatoxines: avantages et inconvénients des différentes méthodes biologiques utilisées [Detection of ciguatoxins: advantages and drawbacks of different biological methods]
- Boydron-Le Garrec Raphaële
- Benoit Evelyne
- Sauviat Martin-Pierre
- Laurent Dominique
Journal de la Société de Biologie , 2005, 199 (2), pp.115-125 . La ciguatera est une intoxication consécutive à la consommation de poissons des récifs contaminés par des toxines spécifiques, les ciguatoxines, à des niveaux capables d'engendrer chez l'Homme une toxicité par voie orale. Les précurseurs de ces toxines sont les gambiertoxines, produites par des Dinoflagellés du genre Gambierdiscus. Ces toxines sont accumulées dans le foie et la chair des poissons brouteurs, herbivores et carnivores, et biotransformées en ciguatoxines plus nocives pour l'Homme. En l'absence de traitement spécifique, la ciguatera reste un problème non seulement de santé publique, mais également socio-économique. La détection des ciguatoxines, au sein des poissons ou de leurs extraits, est donc primordiale et recherchée depuis longtemps. De nombreuses méthodes, biologiques, chimiques ou immunochimiques, ont été développées dans ce but. Cette revue est plus particulièrement centrée sur les méthodes biologiques, développées in vivo ou in vitro, depuis le test de toxicité aiguë sur Souris, maintenant parfaitement standardisé, jusqu'aux méthodes les plus récentes telles que le test de fixation spécifique sur synaptosomes de Rat. Outre la Souris, le Poulet et la Mangouste ont été encore récemment utilisés, notamment pour des tests préliminaires avant l'extraction des ciguatoxines à partir des poissons. Au contraire, diverses autres méthodes in vivo, telles que celles pratiquées sur le Chat, les Culicidés ou les larves de Diptères, furent abandonnées malgré leurs résultats intéressants. Finalement, bien qu'excluant une détection des ciguatoxines sur le terrain, les tests sur neuroblastomes de Souris et synaptosomes de Rat, nouvelles méthodes réalisées in vitro, ont permis un gain considérable tant en sensibilité qu'en spécificité pour détecter les ciguatoxines.
La ciguatera : de l'étiologie du phénomène au traitement de ses symptômes. [Ciguatera: from the etiology of the phenomenon to the treatment of its symptoms]
- Boydron-Le Garrec Raphaële
- Benoit Evelyne
- Sauviat Martin-Pierre
- Frostin Maryvonne
- Laurent Dominique
Journal de la Société de Biologie , 2005, 199(2), pp.127-139 . Ciguatera is the most common food poisoning found in the tropical and subtropical areas, acquired by the consumption of marine products. A lot of work concerning its etiology, its epidemiology and its clinical effects, as well as the discovery of the toxins involved, the description of their transfer, the study of their structure and the analysis of their pharmacological effects, have allowed a better understanding of the ciguateric phenomenon. Ciguatera is known to be due to benthic dinoflagellates belonging to the Gambierdiscus gender, in particular G. toxicus. Under specific conditions, this microalga produces gambier-toxins, toxins which are the precursors of other toxins, the ciguatoxins. However, the factors supporting this production are still poorly known, and the implication of others dinoflagellates, cyanophytes or bacteria have been suspected. In contrast, the fish species responsible for the transmission of ciguatera are globally well identified. The clinical symptoms of the intoxication are now well described. They mainly include digestive, neurological and cardiovascular disorders whose preponderance varies according to the nature of the toxins involved, since toxin structures are different between one ocean and the other. The ciguateric intoxication tends to be exported towards non endemic areas where it is still misdiagnosed. No specific antidote exists to date, and it is only by symptomatic or palliative treatments that ciguatera is currently treated.
Classical calculation of myoglobin circular dichroism spectrum: simulation of a time-resolved experiment
- Dartigalongue Thibault
- Hache François
The Journal of Chemical Physics, American Institute of Physics , 2005, 123, pp.184901 .
Ability of some plant extracts , traditionally used to treat ciguatera fish poisoning, to prevent the in vitro neurotoxicity produced by sodium channel activators.
- Boydron-Le Garrec Raphaële
- Benoit Evelyne
- Sauviat Martin-Pierre
- J. Lewis Richard
- Molgó Jordi
- Laurent Dominique
Toxicon, Elsevier , 2005, 46(6), pp.625-634 . The effects of 31 plant extracts, which most are traditionally used to treat ciguatera fish poisoning in the Pacific area, were studied on the cytotoxicity of mouse neuroblastoma cells produced by ouabain, veratridine and/or brevetoxin-3 or Pacific ciguatoxin-1. The cell viability was determined using a quantitative colorimetric method. A marked cytotoxicity of seven of the 31 plant extracts studied, was observed. Despite this, these plant extracts were suspected to contain active compound(s) against the cytotoxicity produced by brevetoxin (2 extracts), brevetoxin, ouabain and/or veratridine (3 extracts), or only against that of ouabain and/or veratridine (2 extracts). Among the 24 plant extracts that exhibited by themselves no cytotoxicity, 22 were active against the effect of brevetoxin or against that of both veratridine and brevetoxin. Similar results were obtained when the seven most active plant extracts were reassayed using ciguatoxin instead of brevetoxin. In conclusion, the present work reports the first activity assessment of some plant extracts, achieved in vitro on a quite large scale. The fact that 27 plant extracts were found to exert, in vitro, a protective effect against the action of ciguatoxin and/or brevetoxin, paves the way for finding new active compounds to treat ciguatera fish poisoning, provided these compounds also reverse the effects of sodium channel activators. (10.1016/j.toxicon.2005.07.002)
DOI : 10.1016/j.toxicon.2005.07.002
Observation of sub-100 ps conformational changes in photolyzed carbonmonoxy-myoglobin probed by time-resolved circular dichroism
- Dartigalongue Thibault
- Hache François
Chemical Physics Letters, Elsevier , 2005, 415 (4-6), pp.313-316 . A time-resolved circular dichroism (CD) experiment is carried out on carbonmonoxy-myoglobin. The CD is measured with a sub-picosecond time resolution after ligand dissociation and the data are interpreted thanks to a classical CD calculation based on the polarizability theory. We observe a decrease of the CD signal in a few picoseconds and a sub-100 ps relaxation towards steady-state deoxy-myoglobin values which we assign to a stress of the proximal histidine which relaxes with the global reorganization of the protein from its liganded geometry to its deliganded one. 2005 Elsevier B.V. All rights reserved (10.1016/j.cplett.2005.09.022)
DOI : 10.1016/j.cplett.2005.09.022
Nonlinear optical spectroscopy of chiral molecules
- Fischer Peer
- Hache François
Chirality, Wiley , 2005, 17 (8), pp.421 . We review nonlinear optical processes that are specific to chiral molecules in solution and on surfaces. In contrast to conventional natural optical activity phenomena, which depend linearly on the electric field strength of the optical field, we discuss how optical processes that are nonlinear (quadratic, cubic, and quartic) functions of the electromagnetic field strength may probe optically active centers and chiral vibrations. We show that nonlinear techniques open entirely new ways of exploring chirality in chemical and biological systems: The cubic processes give rise to nonlinear circular dichroism and nonlinear optical rotation and make it possible to observe dynamic chiral processes at ultrafast time scales. The quadratic second-harmonic and sum-frequency-generation phenomena and the quartic processes may arise entirely in the electric-dipole approximation and do not require the use of circularly polarized light to detect chirality. They provide surface selectivity and their observables can be relatively much larger than in linear optical activity. These processes also give rise to the generation of light at a new color, and in liquids this frequency conversion only occurs if the solution is optically active. We survey recent chiral nonlinear optical experiments and give examples of their application to problems of biophysical interest. Cop. 2005 Wiley-Liss, Inc. (10.1002/chir.20179)
DOI : 10.1002/chir.20179
Téléphonie cellulaire et cancer: où en est-on? [Cellular phones and cancer: Current status]
- Colonna Anne
Bulletin du Cancer, Elsevier , 2005, 92 (7), pp.637 . L'évaluation de l'impact des nouvelles technologies sur le corps humain est indispensable pour imposer les normes réglementaires limitant les risques sanitaires. L'apparition et l'évolution des téléphones cellulaires ont été parmi les plus rapides dans l'histoire des innovations. De nombreuses recherches ont été effectuées pour tenter d'évaluer le lien éventuel entre effet sur la santé et téléphonie mobile, au niveau du téléphone cellulaire mais également des stations de base. Cet article présente un aperçu des connaissances en matière de recherche sur l'incidence des ondes radiofréquences. Études épidémiologiques, cellulaires et animales se succèdent mais aucune conclusion définitive n'a pu être établie. Même si certains effets biologiques sur des cellules en culture ont été observés, le lien avec un possible développement de cancer chez l'homme reste encore loin d'être établi. Les études animales montrent pour la plupart des résultats négatifs. Quant aux études épidémiologiques, elles manquent d'un recul suffisant pour pouvoir évaluer l'effet des technologies utilisées aujourd'hui. Face à l'inquiétude des populations, opérateurs de téléphonie mobile, constructeurs et instances gouvernementales financent nombre de projets scientifiques afin de permettre une réglementation adaptée et efficace. [Evaluation of the impact of new technologies on the human body is essential in order to impose regulations to limit health risks. The appearance and evolution of cellular phones have been one of the fastest in the history of innovation. Research reported worldwide has tried to evaluate any potential link between adverse health effects and the mobile phone and its broadcasting stations. This article gives an overview of current research knowledge on the impact of radiofrequency waves on health. Epidemiologic, cellular and animal studies have been carried out, but none of them have reached definitive conclusions. Although some biological effects on cell culture have been observed, their link with human cancer development is far from established. Most of the animal studies show negative results. Epidemiologic studies lack a sufficient perspective to be able to evaluate the effect of evolving technologies used today. High levels of concern by the public have urged mobile phone operators, manufacturers and governmental authorities to finance a number of scientific projects aimed at defining adapted and effective regulations.] Cop. John Libbey Eurotext.
Spectroscopic analysis of keratin endogenous signal for skin multiphoton microscopy
- Pena Ana-Maria
- Strupler Mathias
- Boulesteix Thierry
- Schanne-Klein Marie-Claire
Optics Express, Optical Society of America - OSA Publishing , 2005, 13 (16), pp.6268-6274 . We recorded one-photon excited fluorescence (1PEF) and two-photon excited fluorescence (2PEF) spectra of purified keratin from human epidermis, and determined the action cross section of this endogenous chromophore. We used this spectroscopic analysis to analyse multiphoton images of skin biopsies and assign the intrinsic fluorescence signals in the epidermis. We observed a good agreement between in situ and in vitro 2PEF spectra of keratin. This study provides a comprehensive characterization of the 2PEF signal of the keratins from the epidermis, and will be of practical interest for multiphoton imaging of the skin. © 2005 Optical Society of America (10.1364/OPEX.13.006268)
DOI : 10.1364/OPEX.13.006268
Nonlinear spectroscopy of chiral molecules
- Fischer P.
- Hache François
Chirality, Wiley , 2005, 17, pp.421-437 .
Calculation of the circular dichroism spectra of carbon monoxy- and deoxy myoglobin: interpretation of a time-resolved circular dichroism experiment.
- Dartigalongue Thibault
- Hache François
The Journal of Chemical Physics, American Institute of Physics , 2005, 123 (18), pp.184901 . A calculation of the circular dichroism (CD) spectra of carbon monoxy- and deoxy myoglobin is carried out in relation with a time-resolved CD experiment. The calculation is based on the polarizability theory and the parameters are adjusted to fit the experimental absorption and CD spectra. By performing the calculation for intermediate configurations of the protein, we are able to propose an explanation of the CD structure observed on a sub-100 ps time scale. The role of the proximal histidine is, in particular, clearly demonstrated in the first step of the myoglobin relaxation from its liganded to it deliganded form. (10.1063/1.2041467)
DOI : 10.1063/1.2041467
Geminate carbon monoxide rebinding to a c-type haem
- Silkstone G.
- Jasaitis Audrius
- Vos Marten H.
- Wilson M.
Dalton Transactions, Royal Society of Chemistry , 2005, 21 (7), pp.3489 . A chemically modified form of cytochrome c (cyt. c), termed carboxymethyl cytochrome c (cm cyt. c), possesses a vacant sixth coordination site to the haem iron that is available to bind external ligands. We present data on the rapid flash photolysis of CO from the ferrous haem iron of cm cyt. c and describe the kinetics and spectral transitions that accompany the recombination. This was achieved using 30-femtosecond laser pulses and a white light continuum to monitor spectral transitions. Whereas the photo-dissociation quantum yield is close to 1, the yield of CO escape from the protein (the apparent quantum yield, φ) relative to myoglobin (φ = 1) is small due to rapid geminate recombination of CO. On ligand photo-dissociation the haem undergoes a spin-state transition from low-spin ferrous CO bound to penta-coordinate high-spin. Subsequently the system reverts to the CO bound form. The data were fitted with a minimum number of exponentials using global analysis. Recombination of CO with the haem iron of cm cyt. c is multiphasic (τ = 16 ps, 120 ps and 1 ns), involving three spectrally distinct components. The fraction of haem (0.11) not recombining with CO within 4 ns is similar to the value of φ (0.12) measured on the same preparation by the "pulse method" (M. Brunori, G. Giacometti, E. Antonini and J. Wyman, Proc. Natl. Acad. Sci. USA, 1973, 70, 3141-3144, ). This implies that no further geminate recombination occurs at t > 4 ns. This unusually efficient CO-haem geminate recombination indicates the sterically hindered ("caged") nature of the distal haem pocket in cm cyt. c from which it is difficult for CO to escape. The large geminate phase may be contrasted with the behaviour of myoglobin in which geminate recombination is small. This is in general agreement with the well-documented extensive structural dynamics in myoglobin that allow ligand passage, and a higher structural rigidity in cyt. c imposed by the restraints of minimising reorganisation energy for electron transfer (M. Brunori, D. Bourgeois and D. Vallone, J. Struct. Biol., 2004, 147, 223-234, ). The high pH ferrous form of cm cyt. c is a low-spin species having a lysine bound to the central iron atom of the haem (M. Brunori, M. Wilson and E. Antonini, J. Biol. Chem., 1972, 247, 6076-6081; G. Silkstone, G. Stanway, P. Brzezinski and M. Wilson, Biophys. Chem., 2002, 98, 65-77, ). This high pH (pH 8) form of deoxy cm cyt. c undergoes photo-dissociation of lysine (although the proximal histidine is possible) after photo-excitation. Recombination occurs with a time constant (τ) of 7 ps. This is similar to that observed for the geminate rebinding of the Met80 residue in native ferrous cyt. c (τ 6 ps) following its photo-dissociation (S. Cianetti, M. Negrerie, M. Vos, J.-L. Martin and S. Kruglik, J. Am. Chem. Soc., 2004, 126, 13932-13933; W. Wang, X. Ye, A. Demidov, F. Rosca, T. Sjodin, W. Cao, M. Sheeran and P. Champion, J. Phys. Chem., 2000, 104, 10789-10801, ). (10.1039/B508183C)
DOI : 10.1039/B508183C
Retinal isomerization dynamics in dry bacteriorhodopsin films
- Colonna Anne
- Groma Geza I.
- Vos Marten H.
Chemical Physics Letters, Elsevier , 2005, 415 (1-3), pp.69-73 . The primary photoprocesses in neutral and acid forms of oriented dried bacteriorhodopsin films were investigated by femtosecond absorption spectroscopy. The excitation energy dependence of the signals was used to distinguish photochemistry from processes involving photophysics of photocycle intermediates. Both the kinetics and the quantum yield of all-trans excited state decay by retinal photoisomerization and subsequent J → K transition were found to be very similar as in hydrated environments. Therefore, unlike slower photocycle phases, communication of the retinal with the environment does not play a role in retinal isomerization. Our results are important for understanding recent nonlinear optical applications of such films. (10.1016/j.cplett.2005.08.132)
DOI : 10.1016/j.cplett.2005.08.132
Fourier transform measurement of two-photon excitation spectra: applications to microscopy and optimal control
- Ogilvie Jennifer P.
- Kubarych Kevin J.
- Alexandrou Antigoni
- Joffre Manuel
Optics Letters, Optical Society of America - OSA Publishing , 2005, 30, pp.911 . We report a novel Fourier transform method for measuring two-photon excitation spectra. We demonstrate this method using simple dye molecules and discuss its applications in two-photon fluorescence microscopy and optimal control. This method facilitates an intuitive interpretation of recent control experiments in terms of tuning the nonlinear spectrum of the exciting laser source.
Chiroptical effects in the second harmonic signal of collagens I and IV
- Pena Ana-Maria
- Boulesteix Thierry
- Dartigalongue Thibault
- Schanne-Klein Marie-Claire
Journal of the American Chemical Society, American Chemical Society , 2005, 127 (29), pp.10314 . We performed polarization-resolved surface second harmonic generation (SHG) experiments on thin films of collagen I and IV molecules, as well as conventional CD measurements. We found that collagen IV presents little CD and no SHG optical activity, whereas collagen I exhibits large chiroptical effects involving both one-electron and excitonic coupling mechanisms. We estimated that these chiral components enhance the SHG signal from fibrillar collagen in biological tissues by typically a factor of 2. By comparing the distinct behaviors of collagens I and IV in SHG microscopy and in surface SHG experiments, we concluded that SHG microscopy is a sensitive probe of the micrometer-scale structural organization of collagen in biological tissues. Cop. 2005 American Chemical Society. (10.1021/ja0520969)
DOI : 10.1021/ja0520969
Electrical activity alterations induced by chronic absorption of lindane (gamma-hexachlorocyclohexane) trace concentrations in adult rat heart
- Sauviat Martin-Pierre
- Bouvet Suzanne
- Godeau Gaston
- Pages Nicole
Canadian Journal of Physiology and Pharmacology, NRC Research Press , 2005, 83 (3), pp.243 . The heart of adult rat offspring, born to mothers treated with trace concentrations of lindane (0.5 to 2 ppb) through a beverage and to mothers chronically treated with lindane (CL-T) with the same trace concentration, also through a beverage, during lactation and growth has a round shape and accumulates lindane. The left ventricle (LV) presents a hypertrophied area, atrophied papillary muscles, and unorganized collagen bundles and layers. These observations led us to study the electrical activity of their left ventricle papillary muscles (LVPM) by recording action potential using intracellular microelectrodes. CL-T shortened LVPM action potential duration (APD): 1 ppb shortened the plateau; 2 ppb shortened the plateau and the slow repolarizing phase. In CL-T (2 ppb) and untreated groups, low temperature (22 degrees C) decreased the resting potential and prolonged APD. TEA (tetraethylammonium; 1-2 mmol/L) partially lengthened CL-T (2 ppb lindane) APD. Quinidine (0.2 mmol/L) and E-4031 (10 nmol/L) prolonged CL-T APD, suggesting that the rapid delayed outward K+ current (I-Kr) was increased. Our results indicate the silent effects of chronic exposure to trace concentrations of lindane on the morphological and electrical activity of heart muscle. They demonstrate that chronic lindane treatment of female rats alters the tissue integrity and electrical activity in the LV of their offspring. (10.1139/Y04-132)
DOI : 10.1139/Y04-132
In vivo modulation of morphogenetic movements in Drosophila embryos with femtosecond laser pulses
- Supatto Willy
- Débarre Delphine
- Moulia Bruno B.
- Brouzés Eric
- Martin Jean-Louis
- Farge Emmanuel
- Beaurepaire Emmanuel
Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences , 2005, 102 (4), pp.1047 . The complex biomechanical events associated with embryo development are investigated in vivo, by using femtosecond laser pulse-induced ablation combined with multimodal nonlinear microscopy. We demonstrate controlled intravital ablations preserving local cytoskeleton dynamics and resulting in the modulation of specific morphogenetic movements in nonmutant Drosophila embryos. A quantitative description of complex movements is obtained both in GFP-expressing systems by using whole-embryo two-photon microscopy and in unlabeled nontransgenic embryos by using third harmonic generation microscopy. This methodology provides insight into the issue of mechano-sensitive gene expression by revealing the correlation of in vivo tissue deformation patterns with Twist protein expression in stomodeal cells at gastrulation. (10.1073/pnas.0405316102)
DOI : 10.1073/pnas.0405316102
Velocimetric third-harmonic generation microscopy: micrometer-scale quantification of morphogenetic movements in unstained embryos
- Débarre Delphine
- Supatto Willy
- Farge Emmanuel
- Moulia Bruno B.
- Schanne-Klein Marie-Claire
- Beaurepaire Emmanuel
Optics Letters, Optical Society of America - OSA Publishing , 2004, 29, pp.2881-2883 . We demonstrate the association of third-harmonic generation (THG) microscopy and particle image velocimetry (PIV) analysis as a novel functional imaging technique for automated micrometer-scale characterization of morphogenetic movements in developing embryos. Using a combined two-photon-excited fluorescence and THG microscope, we characterize the optical properties of Drosophila embryos and show that sustained THG imaging does not perturb sensitive developmental dynamics. Velocimetric THG imaging provides a quantitative description of the dynamics of internal structures in unstained wild-type and mutant embryos. (10.1364/OL.29.002881)
DOI : 10.1364/OL.29.002881
Second-harmonic microscopy of unstained living cardiac myocytes: measurements of sarcomere length with 20-nm accuracy.
- Boulesteix Thierry
- Beaurepaire Emmanuel
- Sauviat Martin-Pierre
- Schanne-Klein Marie-Claire
Optics Letters, Optical Society of America - OSA Publishing , 2004, 29 (17), pp.2031-3 . We extend second-harmonic generation (SHG) microscopy to the measurement of sarcomere length in unstained living cardiac myocytes with 20-nm accuracy. We quantify individual sarcomere shortening in the presence of saxitoxin and find that it is in agreement with mechanical measurements of atrial tissue contracture. This functional application of SHG microscopy is generally applicable to quantify the physiological effects of drugs on contractile tissue. Our data also suggest that packed myosin heads in sarcomere thick filaments are responsible for the large second-harmonic endogenous signal in muscle tissue. (10.1364/OL.29.002031)
DOI : 10.1364/OL.29.002031
From The Cover: An aminoacyl-tRNA synthetase-like protein encoded by the Escherichia coli yadB gene glutamylates specifically tRNAAsp
- Dubois Daniel
- Blaise Mickaël
- Becker Hubert F.
- Campanacci Valérie
- Keith Gerard
- Cambillau Christian
- Lapointe Jacques
- Kern Daniel
- Becker D.
- Giegé Richard
Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences , 2004, 101 (20), pp.7530-7535 . The product of the Escherichia coli yadB gene is homologous to the N-terminal part of bacterial glutamyl-tRNA synthetases (GluRSs), including the Rossmann fold with the acceptor-binding domain and the stem-contact fold. This GluRS-like protein, which lacks the anticodon-binding domain, does not use tRNA(Glu) as substrate in vitro nor in vivo, but aminoacylates tRNA(Asp) with glutamate. The yadB gene is expressed in wild-type E. coli as an operon with the dksA gene, which encodes a protein involved in the general stress response by means of its action at the translational level. The fate of the glutamylated tRNA(Asp) is not known, but its incapacity to bind elongation factor Tu suggests that it is not involved in ribosomal protein synthesis. Genes homologous to yadB are present only in bacteria, mostly in Proteobacteria. Sequence alignments and phylogenetic analyses show that the YadB proteins form a distinct monophyletic group related to the bacterial and organellar GluRSs (alpha-type GlxRSs superfamily) with ubiquitous function as suggested by the similar functional properties of the YadB homologue from Neisseria meningitidis. (10.1073/pnas.0401634101)
DOI : 10.1073/pnas.0401634101
Resonant optical rectification in bacteriorhodopsin
- Groma Géza
- Colonna Anne
- Lambry Jean-Christophe
- Petrich Jacob
- Váró G.
- Joffre Manuel
- Vos Marten H.
- Martin Jean-Louis
Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences , 2004, 101 (21), pp.7971 . The relative role of retinal isomerization and microscopic polarization in the phototransduction process of bacteriorhodopsin is still an open question. It is known that both processes occur on an ultrafast time scale. The retinal trans?cis photoisomerization takes place on the time scale of a few hundred femtoseconds. On the other hand, it has been proposed that the primary light-induced event is a sudden polarization of the retinal environment, although there is no direct experimental evidence for femtosecond charge displacements, because photovoltaic techniques cannot be used to detect charge movements faster than picoseconds. Making use of the known high second-order susceptibility ?(2) of retinal in proteins, we have used a nonlinear technique, interferometric detection of coherent infrared emission, to study macroscopically oriented bacteriorhodopsin-containing purple membranes. We report and characterize impulsive macroscopic polarization of these films by optical rectification of an 11-fs visible light pulse in resonance with the optical transition. This finding provides direct evidence for charge separation as a precursor event for subsequent functional processes. A simple two-level model incorporating the resonant second-order optical properties of retinal, which are known to be a requirement for functioning of bacteriorhodopsin, is used to describe the observations. In addition to the electronic response, long-lived infrared emission at specific frequencies was observed, reflecting charge movements associated with vibrational motions. The simultaneous and phase-sensitive observation of both the electronic and vibrational signals opens the way to study the transduction of the initial polarization into structural dynamics. (10.1073/pnas.0306789101)
DOI : 10.1073/pnas.0306789101
Excited-state properties of flavin radicals in flavoproteins: Femtosecond spectroscopy of DNA photolyase, glucose oxidase, and flavodoxin
- Pan Jie
- Byrdin Martin
- Aubert Corinne
- Eker André P. M.
- Brettel Klaus
- Vos Marten H.
Journal of Physical Chemistry B, American Chemical Society , 2004, 108 (28), pp.10160 . In isolated, catalytically inactive, DNA photolyase from Escherichia coli (E. coli), the flavin adenine dinucleotide cofactor is in its neutral radical state FAD?. It can be activated by a unique light-induced reduction of the flavin, a process initiated by the formation of the excited-state FAD?*. As the photophysical properties of this state are essentially unknown, we performed a comparative characterization by femtosecond transient absorption spectroscopy of FAD?* in DNA photolyase from E. coli and glucose oxidase from Aspergillus niger, and of the excited neutral radical flavin mononucleotide (FMN?*) in flavodoxin from Desulfovibrio gigas. In contrast to photolyase, in glucose oxidase and flavodoxin no electron-transfer products are observed after selective excitation of the flavin radical. In glucose oxidase, FAD?* decays to the ground state in 59 ± 5 ps, close to the 80-ps intrinsic lifetime of the excited state in photolyase, and we discuss that the intrinsic lifetime of the excited state of flavin radical in protein environment is in the 50-80 ps range. FMN?* in flavodoxin decays much faster (2.3 ± 0.3 ps), possibly because of quenching by formation of a very short-lived (INF 0.7 ps) electron-transfer intermediate. Spectroscopically, the excited state of FAD? in photolyase displays a pronounced spectral feature that is absent in the other systems studied. Further characterization by polarized photoselection experiments identifies the feature as an additional induced absorption band at ~ 550 nm superimposed on the ground-state bleaching signal. In view of the unique U-shape configuration of FAD in photolyase, we suggest it to reflect a flavin-adenine charge-transfer interaction.
Functionalized fluorescent oxide nanoparticles: Artificial toxins for sodium channel targeting and imaging at the single-molecule level
- Beaurepaire Emmanuel
- Buissette Valérie
- Sauviat Martin-Pierre
- Giaume Domitile
- Lahlil Khalid
- Mercuri Antoine
- Casanova Didier
- Huignard Arnaud
- Martin Jean-Louis
- Gacoin Thierry
- Boilot Jean-Pierre
- Alexandrou Antigoni
Nano Letters, American Chemical Society , 2004, 4 (11), pp.2079-2083 . Lanthanide ion-doped oxide nanoparticles were functionalized for use as fluorescent biological labels. These nanoparticles are synthesized directly in water, which facilitates their functionalization, and are remarkably photostable without emission intermittency. Nanoparticles functiqnalized with guanidinium groups act as artificial toxins and specifically target sodium channels. They are individually detectable in live cardiac myocytes, revealing a heterogeneous distribution of sodium channels. Functionalized oxide nanoparticles appear to be a novel tool that is particularly attractive for long-term single-molecule tracking. (10.1021/nl049105g)
DOI : 10.1021/nl049105g
Application of the polarizability theory to the calculation of anisotropic circular dichroism spectra
- Hache François
- Dartigalongue Thibault
Chemical Physics, Elsevier , 2004, 303 (1-2), pp.197-203 . We derive a general expression of the circular dichroism spectra of anisotropically distributed chiral molecules in the polarizability framework by introducing a tensorial rotational strength. Example calculation is carried out on an acridine-substituted Tröger base. It is shown that the circular dichroism is very sensitive to the direction propagation of the light beam. (10.1016/j.chemphys.2004.05.021)
DOI : 10.1016/j.chemphys.2004.05.021
CO Vibration as a Probe of Ligand Dissociation and Transfer in Myoglobin
- Polack Thomas
- Ogilvie Jennifer P.
- Franzen S.
- Vos Marten H.
- Joffre Manuel
- Martin Jean-Louis
- Alexandrou Antigoni
Physical Review Letters, American Physical Society , 2004, 93 (1), pp.18102 . We report femtosecond visible pump, midinfrared probe, spectrally integrated experiments resolving the dynamics of CO in myoglobin upon photodissociation. Our results show a progressive change in absorption strength of the CO vibrational transition during its transfer from the heme to the docking site, whereas the vibrational frequency change is faster than our time resolution. A phenomenological model gives good qualitative agreement with our data for a time constant of 400 fs for the change in oscillator strength. Density-functional calculations demonstrate that indeed vibrational frequency and absorption strength are not linearly coupled and that the absorption strength varies in a slower manner due to charge transfer from the heme iron to CO (10.1103/PhysRevLett.93.018102)
DOI : 10.1103/PhysRevLett.93.018102