Publications

2016

• Forward versus backward polarization-resolved SHG imaging of collagen structure in tissues
  
  • Teulon Claire
  • Gusachenko Ivan
  • Latour Gaël
  • Schanne-Klein Claire
  , 2016, 9712, pp.971218. Second harmonic generation (SHG) is a powerful technique to observe fibrillar collagen without any staining and with a good contrast. More information about the molecular structure of collagen fibrils in tissues and their 3D distribution can be gained with polarization-resolved SHG imaging. Nevertheless, strong focusing is required for effective imaging and light propagation in tissues is complex and not thoroughly understood yet, preventing accurate and reproducible measurements. Theoretical analysis, vectorial numerical simulations and experiments were implemented to understand how the SHG signal builds up and how geometrical parameters affect polarization-resolved measurements in homogeneous collagen-rich tissues (10.1117/12.2208110)
  DOI : 10.1117/12.2208110
• Quantum calculation of the second-order hyperpolarizability of chiral molecules in the "one-electron" model
  
  • Hache François
  , 2016, 9745. Second-harmonic generation in chiral molecules has been thoroughly studied, especially in surface experiments. On a molecular viewpoint, the linear optical properties of chiral molecules necessitate to include the magnetic dipole response, but such is not the case for second-order nonlinear optics where fully electric-dipole response is sufficient. We propose here a full quantum-mechanical calculation of the hyperpolarizability of chiral molecules in the "one-electron" model which shows that (i) such chiral molecules are inherently nonlinear and (i) for nonlinear response, achiral and chiral contributions can have the same order of magnitude, contrarily to what is observed in linear optics. (10.1117/12.2217662)
  DOI : 10.1117/12.2217662
• Ultrafast Spectroscopy Evidence for Picosecond Ligand Exchange at the Binding Site of a Heme Protein: Heme-Based Sensor YddV
  
  • Lambry Jean-Christophe
  • Stranava Martin
  • Lobato Laura
  • Martinkova Marketa
  • Shimizu Toru
  • Liebl Ursula
  • Vos Marten H.
  Journal of Physical Chemistry Letters, American Chemical Society, 2016, 7 (1), pp.69-74. An important question for the functioning of heme proteins is whether different ligands present within the protein moiety can readily exchange with heme-bound ligands. Studying the dynamics of the heme domain of the Escherichia coli sensor protein YddV upon dissociation of NO from the ferric heme by ultrafast spectroscopy, we demonstrate that when the hydrophobic leucine residue in the distal heme pocket is mutated to glycine, in a substantial fraction of the protein water replaces NO as an internal ligand in as fast as ∼4 ps. This process, which is near-barrierless and occurs orders of magnitude faster than the corresponding process in myoglobin, corresponds to a ligand swap of NO with a water molecule present in the heme pocket, as corroborated by molecular dynamics simulations. Our findings provide important new insight into ligand exchange in heme proteins that functionally interact with different external ligands. (10.1021/acs.jpclett.5b02517)
  DOI : 10.1021/acs.jpclett.5b02517
• Probing the 3D structure of cornea-like collagen liquid crystals with polarization-resolved SHG microscopy
  
  • Teulon Claire
  • Tidu Aurélien
  • Portier François
  • Mosser Gervaise
  • Schanne-Klein Marie-Claire
  Optics Express, Optical Society of America - OSA Publishing, 2016, 24, pp.16084 - 10. This work aims at characterizing the three-dimensional organization of liquid crystals composed of collagen, in order to determine the physico-chemical conditions leading to highly organized structures found in biological tissues such as cornea. To that end, we use second-harmonic generation (SHG) microscopy, since aligned collagen structures have been shown to exhibit intrinsic SHG signals. We combine polarization-resolved SHG experiments (P-SHG) with the theoretical derivation of the SHG signal of collagen molecules tilted with respect to the focal plane. Our P-SHG images exhibit striated patterns with variable contrast, as expected from our analytical and numerical calculations for plywood-like nematic structures similar to the ones found in the cornea. This study demonstrates the benefits of P-SHG microscopy for in situ characterization of highly organized biopolymers at micrometer scale, and the unique sensitivity of this nonlinear optical technique to the orientation of collagen molecules. (10.1364/OE.24.016084.v001)
  DOI : 10.1364/OE.24.016084.v001
• Three-photon microscopy with a monolithic all-fiber format laser emitting at 1650 nm
  
  • Cadroas P
  • Kotov L.
  • Abdeladim L.
  • Gomes J.T.
  • Likhachev M.
  • Supatto W.
  • Lipatov D.
  • Tang M.
  • Hideur Ammar
  • Beaurepaire Emmanuel
  • Février Sébastien
  , 2016. One optimal window for biological imaging lies around 1675 ± 20 nm wavelength, a result of the decreased effects of both tissue scattering and water absorption. Furthermore, in nonlinear microscopy the signal-to-background ratio, which limits the maximum penetration depth, is dramatically increased with increasing photon order. As a consequence, three-photon microscopy with an excitation wavelength of approximately 1675 nm was recently proposed as a promising approach for deep microscopic imaging of live tissues. Wide adoption of this technique will rely on cost-effective and environmentally insensitive lasers operating at this exotic wavelength. In this communication we report on a monolithically integrated high repetition rate all-fiber femtosecond laser operating in the spectral range from 1650 to 1700 nm. The laser is based on custom-designed large mode area erbium-doped fiber operated in the nonlinear regime. We explore its potential for biological microscopy by imaging live embryonic tissue. (10.1109/ICTON.2016.7550407)
  DOI : 10.1109/ICTON.2016.7550407
• Laser femtoseconde entierement fibre emettant a 1650 nm et application a la microscopie tri-photonique
  
  • Cadroas P
  • Kotov L.
  • Abdeladim L.
  • Likhachev M.
  • Lipatov D.
  • Gomes J.T.
  • Gaponov D.
  • Hideur Ammar
  • Livet J.
  • Supatto W.
  • Beaurepaire Emmanuel
  • Février Sébastien
  , 2016.
• Three-Photon Microscopy with a Monolithic All-Fiber Format Laser Emitting at 1650 nm
  
  • Cadroas Patrick
  • Kotov Leonid
  • Abdeladim L.
  • Gomes J.-T.
  • Likhachev M.
  • Supatto W.
  • Lipatov D.
  • Tang Mincheng
  • Hideur A.
  • Beaurepaire E.
  • Fevrier Sébastien
  , 2016. no abstract
• Direct observation of subpicosecond vibrational dynamics in photoexcited myoglobin
  
  • Ferrante C.
  • Pontecorvo E.
  • Cerullo Giulio
  • Vos Marten H.
  • Scopigno T.
  Nature Chemistry, Nature Publishing Group, 2016 (8), pp.1137–1143. Determining the initial pathway for ultrafast energy redistribution within biomolecules is a challenge, and haem proteins, for which energy can be deposited locally in the haem moiety using short light pulses, are suitable model systems to address this issue. However, data acquired using existing experimental techniques that fail to combine sufficient structural sensitivity with adequate time resolution have resulted in alternative hypotheses concerning the interplay between energy flow among highly excited vibrational levels and potential concomitant electronic processes. By developing a femtosecond-stimulated Raman set-up, endowed with the necessary tunability to take advantage of different resonance conditions, here we visualize the temporal evolution of energy redistribution over different vibrational modes in myoglobin. We establish that the vibrational energy initially stored in the highly excited Franck–Condon manifold is transferred with different timescales into low- and high-frequency modes, prior to slow dissipation through the protein. These findings demonstrate that a newly proposed mechanism involving the population dynamics of specific vibrational modes settles the controversy on the existence of transient electronic intermediates. (10.1038/nchem.2569)
  DOI : 10.1038/nchem.2569
• Predictive modeling targets thymidylate synthase ThyX in Mycobacterium tuberculosis
  
  • Djaout Kamel
  • Singh Vinayak
  • Boum Yap
  • Katawera Victoria
  • Becker Hubert F.
  • Bush Natassja G.
  • Hearnshaw Stephen J.
  • Pritchard Jennifer E.
  • Bourbon Pauline
  • Madrid Peter B.
  • Maxwell Anthony
  • Mizrahi Valerie
  • Myllykallio Hannu
  • Ekins Sean
  Scientific Reports, Nature Publishing Group, 2016, 6, pp.27792. There is an urgent need to identify new treatments for tuberculosis (TB), a major infectious disease caused by Mycobacterium tuberculosis (Mtb), which results in 1.5 million deaths each year. We have targeted two essential enzymes in this organism that are promising for antibacterial therapy and reported to be inhibited by naphthoquinones. ThyX is an essential thymidylate synthase that is mechanistically and structurally unrelated to the human enzyme. DNA gyrase is a DNA topoisomerase present in bacteria and plants but not animals. The current study set out to understand the structure-activity relationships of these targets in Mtb using a combination of cheminformatics and in vitro screening. Here, we report the identification of new Mtb ThyX inhibitors, 2-chloro-3-(4-methanesulfonylpiperazin-1-yl)-1,4-dihydronaphthalene-1,4-dione) and idebenone, which show modest whole-cell activity and appear to act, at least in part, by targeting ThyX in Mtb. (10.1038/srep27792)
  DOI : 10.1038/srep27792