PASTEUR – Page 8 – Département de Chimie de l'ENS

A Dual Functional Electroactive and Fluorescent Probe for Coupled Measurements of Vesicular Exocytosis with High Spatial and Temporal Resolution

In this work, Fluorescent False Neurotransmitter 102 (FFN102), a synthesized analogue of biogenic neurotransmitters, was demonstrated to show both pH-dependent fluorescence and electroactivity. To study secretory behaviors at the single-vesicle level, FFN102 was employed as a new fluorescent/electroactive dual probe in a coupled technique (amperometry and total internal reflection fluorescence microscopy (TIRFM)). We used N13 cells, a stable clone of BON cells, to specifically accumulate FFN102 into their secretory vesicles, and then optical and electrochemical measurements of vesicular exocytosis were experimentally achieved by using indium tin oxide (ITO) transparent electrodes. Upon stimulation, FFN102 started to diffuse out from the acidic intravesicular microenvironment to the neutral extracellular space, leading to fluorescent emissions and to the electrochemical oxidation signals that were simultaneously collected from the ITO electrode surface. The correlation of fluorescence and amperometric signals resulting from the FFN102 probe allows realtime monitoring of single exocytotic events with both high spatial and temporal resolution. This work opens new possibilities in the investigation of exocytotic mechanisms.

Consultez le communiqué de presse associé à cet article : Suivre la communication entre les cellules !

References:
A Dual Functional Electroactive and Fluorescent Probe for Coupled Measurements of Vesicular Exocytosis with High Spatial and Temporal Resolution
Xiaoqing Liu, Alexandra Savy, Sylvie Maurin, Laurence Grimaud, François Darchen, Damien Quinton, Eric Labbé, Olivier Buriez, Jérôme Delacotte, Frédéric Lemaître, and Manon Guille-Collignon
Angew. Chem. Int. Ed. 2017, 56, 1 – 6
DOI: 10.1002/anie.201611145

‘Full fusion’ is not ineluctable during vesicular exocytosis of neurotransmitters by endocrine cells

Vesicular exocytosis is an essential and ubiquitous process in neurons and endocrine cells by which neurotransmitters are released in synaptic clefts or extracellular fluids. It involves the fusion of a vesicle loaded with chemical messengers with the cell membrane through a nanometric fusion pore. In endocrine cells, unless it closes after some flickering (‘Kiss-and-Run’ events), this initial pore is supposed to expand exponentially, leading to a full integration of the vesicle membrane into the cell membrane—a stage called ‘full fusion’.We report here a compact analytical formulation that allows precise measurements of the fusion pore expansion extent and rate to be extracted from individual amperometric spike time courses. These data definitively establish that, during release of catecholamines, fusion pores enlarge at most to approximately one-fifth of the radius of their parent vesicle, hence ruling out the ineluctability of ‘full fusion’.

Consultez le communiqué de presse associé à cet article, rédigé par l’Institut de Chimie du CNRS :
Libération des neurotransmetteurs : une nouvelle porte s’ouvre

References:
‘Full fusion’ is not ineluctable during vesicular exocytosis of neurotransmitters by endocrine cells
Alexander Oleinick, Irina Svir and Christian Amatore
Proc. R. Soc. A 473: 20160684.
Doi : 10.1098/rspa.2016.0684

Médaille de Bronze CNRS

Arnaud GAUTIER, Maître de Conférence ENS, est lauréat de la médaille de Bronze du CNRS, notamment pour le développement et la mise au point de nouveaux marqueurs fluorescents pour l’imagerie biologique.

La Médaille de bronze récompense le premier travail d’un chercheur, qui fait de lui un spécialiste de talent dans son domaine. Cette récompense représente un encouragement du CNRS à poursuivre des recherches bien engagées et déjà fécondes.

Consultez un exemple de sa recherche : Un interrupteur fluorescent pour le marquage des protéines.

Richard G. Compton

Richard G. Compton, Professeur à l’Université d’Oxford est invité par le Laboratoire PASTEUR du Département de Chimie de l’ENS durant le mois de juin 2017. Son équipe d’accueil est le Pôle d’Electrochimie

More information on his research :

Understanding electrochemical processes is key to developing energy storage and conversion devices (fuel cells, solar cells, batteries) as well as being at the heart of much of modern biology and nanotechnology. At the same time electrochemical sensors provide sensitive, selective, clean and easy to use approaches to the detection and monitoring of many important chemical species (gas sensors, blood sugar, pH).

The Compton Group has interests ranging from fundamental electrochemistry (theory of electron transfer and of mass transport) to making chemical sensors; the companies Senova and OxTox have spun out of Group research in recent years. Current work also focuses on electrochemistry in nanoelectrodes, room temperature ionic liquids and in bioelectrochemistry. We adopt a bottom-up approach developing new methods to investigate the kinetics and mechanisms of interfacial reactions.

http://compton.chem.ox.ac.uk/

Chemisorption of Hydroxide on 2D Materials from DFT Calculations: Graphene versus Hexagonal Boron Nitride

Recent nanofluidic experiments revealed strongly diff erent surface charge measurements for boron-nitride (BN) and graphitic nanotubes when in contact with saline and alkaline water (Nature 2013 , 494 , 455− 458; Phys. Rev. Lett. 2016 , 116 , 154501). These observations contrast with the similar reactivity of a graphene layer and its BN counterpart, using density functional theory (DFT) framework, for intact and dissociative adsorption of gaseous water molecules. Here we investigate, by DFT in implicit water, single and multiple adsorption of anionic hydroxide on single layers. A differential adsorption strength is found in vacuum for the first ionic adsorption on the two materials chemisorbed on BN while physisorbed on graphene. The effect of implicit solvation reduces all adsorption values, resulting in a favorable (nonfavorable) adsorption on BN (graphene). We also calculate a pKa around 6 for BN in water, in good agreement with experiments. Comparatively, the unfavorable results for graphene in water echo the weaker surface charge measurements but point to an alternative scenario.

N’hésitez pas à consulter le communiqué de presse associé à cet article : La réactivité anormale des matériaux bidimensionnels.

References:
Chemisorption of Hydroxide on 2D Materials from DFT Calculations: Graphene versus Hexagonal Boron Nitride
Benoit Grosjean, Clarisse Pean, Alessandro Siria, Lydéric Bocquet, Rodolphe Vuilleumier, and Marie-Laure Bocquet
J. Phys. Chem. Lett. 2016, 7, 4695−4700
DOI: 10.1021/acs.jpclett.6b02248

ERC Consolidator Grant

A European Research Council (ERC) Consolidator Grant has been awarded to Arnaud

Gautier, Maître de Conférences at the Department of Chemistry of ENS, for his project

FLUOSWITCH – Pushing the frontiers of biological imaging with genetically encoded

fluorescence switches.

English:

Our understanding of biological systems is intricately related to our ability to observe how

their inner constituents organize and interact. FLUOSWITCH is a multidisciplinary research

project aiming at pushing the frontiers of biological imaging. Combining concepts and

methods from Chemistry and Biology, FLUOSWITCH proposes to develop semi-synthetic

hybrid probes to interrogate quantitatively and comprehensively living systems at the

molecular, cellular and network levels. In the frame of this project, will be generated

molecular systems enabling (i) to push multiplexed imaging to visualize a large number of

targets, (ii) to increase the resolution of live-cell imaging to have a full comprehension of

biological processes both in space and time, (iii) to image endogenous molecules in their

native environment; and (iv) to map circuits of interacting cells in an entire organism.

Français :

Notre compréhension des systèmes biologiques est intimement liée à notre capacité

d’observer comment leurs constituants internes s’organisent et interagissent. Le projet

multidisciplinaire FLUOSWITCH a pour objectif de repousser les limites de l’imagerie

biologique. En combinant des concepts et méthodes issus de la Chimie et de la Biologie,

FLUOSWITCH propose de développer des sondes hybrides semi-synthétiques permettant

d’interroger les systèmes vivants de manière quantitative à de multiples échelles, moléculaire,

cellulaire et systémique. Dans le cadre de se projet, seront générés des systèmes moléculaires

permettant : (i) de repousser les limites de l’imagerie multiplexée pour observer un grand

nombre de cibles, (ii) d’augmenter la résolution spatiotemporelle de l’imagerie cellulaire pour

avoir une meilleure compréhension des processus biologiques, (iii) d’imager les molécules

endogènes dans leur environnement naturel, et (iv) de cartographier des circuits de cellules

actives dans un organisme entier.

FAST : la start-up de chimie théorique – un nouveau paradigme pour le « drug design » !

La conception de nouveaux médicaments, ce qu’on appelle le « drug design », nécessite de nombreuses étapes s’étalant sur plus de 10 ans, pour un coût avoisinant le milliard d’euros. Le drug design consiste en effet à chercher les molécules les plus prometteuses parmi plusieurs millions.

De légères variations dans la formule chimique d’une molécule peuvent avoir une influence considérable sur son affinité avec une protéine, et donc sur son effet thérapeutique. Un facteur clé de cette affinité est l’interaction plus ou moins favorable du site actif de la protéine avec les molécules d’eau qui constituent son environnement immédiat. Prédire et quantifier cette interaction est fondamental pour le « drug design ».

En partant de ce constat et sur la base de travaux de recherche du CNRS et du Pôle de physico-chimie théorique du Département de Chimie de l’ENS, nous proposons FAST (FAst Solvation Tool) :

· FAST est une solution logicielle pour calculer et visualiser en 3D les interactions entre l’eau et n’importe quelle molécule, médicament ou protéine.

· FAST exploite une théorie basée sur 10 ans de recherche fondamentale en thermodynamique statistique au sein du Département de Chimie de l’ENS.

· FAST est 1000 à 10 000 fois plus rapide que les solutions proposées sur le marché.

· FAST est la solution pour réduire les coûts de conception et accélérer la sélection de molécules thérapeutiques en drug design.

FAST est une start-up localisée au sein du Département de Chimie de l’ENS constituée de 3 membres : Maximilien Levesque, CR CNRS, Guillaume Jeanmairet, ancien élève chimie ENS, actuellement post-doctorant, et Cédric Gageat, doctorant chimie ENS.

Maximilien Levesque, Guillaume Jeanmairet et Cédric Gageat : la FAST team !

Le 24 novembre 2016, FAST a été lauréat du public et du collège des ingénieurs du « Prix des startups normaliennes » organisé par le Club des normaliens dans l’entreprise, en partenariat avec Idinvest Partners, PwC et le Collège des Ingénieurs.

Téléchargez le communiqué de presse :
FAST : la start-up de chimie théorique – un nouveau paradigme pour le « drug design » !

Protein Adsorption and Reorganization on Nanoparticles Probed by the Coffee- Ring Effect: Application to Single Point Mutation Detection

The coffee-ring effect denotes the accumulation of particles at the edge of an evaporating sessile drop pinned on a substrate. Because it can be detected by simple visual inspection, this ubiquitous phenomenon can be envisioned as a robust and cost-effective diagnostic tool. Toward this direction, here we systematically analyze the deposit morphology of drying drops containing polystyrene particles of different surface properties with various proteins (bovine serum albumin (BSA) and diff erent forms of hemoglobin). We show that deposit patterns reveal information on both the adsorption of proteins onto particles and their reorganization following adsorption. By combining pattern analysis with adsorption isotherm and zeta potential measurements, we show that the suppression of the coffee-ring effect and the formation of a disk-shaped pattern is primarily associated with particle neutralization by protein adsorption. However, our fi ndings also suggest that protein reorganization following adsorption can dramatically invert this tendency. Exposure of hydrophobic (respectively charged) residues can lead to disk (respectively ring) deposit morphologies independently of the global particle charge. Surface tension measurements and microscopic observations of the evaporating drops show that the determinant factor of the deposit morphology is the accumulation of particles at the liquid/gas interface during evaporation. This general behavior opens the possibility to probe protein adsorption and reorganization on particles by the analysis of the deposit patterns, the formation of a disk being the robust signature of particles rendered hydrophobic by protein adsorption.

N’hésitez pas à consulter le communiqué de presse associé à cet article : Détecter une maladie génétique avec une « tache de café » !

References:
Protein Adsorption and Reorganization on Nanoparticles Probed by the Coffee-Ring Effect: Application to Single Point Mutation Detection
Devineau S, Anyfantakis M, Marichal L, Kiger L, Morel M, Rudiuk S, Baigl D.
J. Am. Chem. Soc 2016, 138, 11623–11632
doi: 10.1021/jacs.6b04833

Ultrafast Dynamics of a Green Fluorescent Protein Chromophore Analogue: Competition between Excited-State Proton Transfer and Torsional Relaxation

The competition between excited-state proton transfer (ESPT) and torsion plays a central role in the photophysics of fluorescent proteins of the green fluorescent protein (GFP) family and their chromophores. Here, it was investigated in a single GFP chromophore analogue bearing o-hydroxy and p-diethylamino substituents, OHIM. The light-induced dynamics of OHIM was studied by femtosecond transient absorption spectroscopy, at different pH. We found that the photophysics of OHIM is determined by the electron-donating character of the diethylamino group: torsional relaxation dominates when the diethylamino group is neutral, whereas ultrafast ESPT followed by cis/trans isomerization and ground-state reprotonation are observed when the diethylamino group is protonated and therefore inactive as an electron donor.

N’hésitez pas à consulter le communiqué de presse relatif à cet article : La dynamique d’un chromophore fluorescent à l’étude !

References:
Ultrafast Dynamics of a Green Fluorescent Protein Chromophore Analogue: Competition between Excited-State Proton Transfer and Torsional Relaxation
Chatterjee, T, Lacombat F, Yadav D, Mandal M, Plaza P, Espagne A, Mandal PK
J. Phys. Chem. B, 2016, 120 (36), pp 9716–9722
DOI: 10.1021/acs.jpcb.6b05795

Prix Arconati-Visconti de la Chancellerie des Universites de Paris

Elise Duboué-Dijon a reçu le prix Arconati-Visconti 2016 de la chancellerie des universités pour sa thèse de doctorat effectuée au pôle de physico-chimie théorique du département de chimie de l’ENS sous la direction de Damien Laage.

La Chancellerie décerne chaque année 50 prix solennels. Les prix solennels récompensent l’excellence de la valeur universitaire et scientifique d’une thèse de doctorat soutenue au cours de l’année civile précédant l’année d’attribution. Ils s’adressent à tous les étudiants franciliens en droit et sciences politiques, sciences économiques et gestion, médecine et sciences, lettres et sciences humaines et pharmacie.