• facebook
  • pinterest
  • twitter
  • rss
  • mail
  • Annuaire
  • Intranet
  • Webmail
  • Cloud
  • Contacts
  • Accès
  • Switch Language
    • frFrançais
    • enEnglish (Anglais)
INSTITUT DE PHYSIQUE ET DE CHIMIE DES MATERIAUX DE STRASBOURG
  • Laboratoire
    • Présentation
    • Organigramme
    • Services généraux
    • Notre politique qualité
    • Publications
    • Valorisation
    • Actualités
    • Evénements
    • Séminaires IPCMS
    • IPCMS en chiffres
    • ADDEPT
    • Actions grand public
    • 30 ans de l’IPCMS
  • Départements
    • Chimie des Matériaux Inorganiques (DCMI)
    • Matériaux Organiques (DMO)
    • Magnétisme des Objets NanoStructurés (DMONS)
    • Optique ultra-rapide et Nanophotonique (DON)
    • Surfaces et Interfaces (DSI)
  • Enseignement
    • Formations UNISTRA
    • Ecoles Doctorales
    • Master Matière Condensée et Nanophysique
    • Master Matériaux et Nanosciences (MNS)
    • Master Imagerie, Robotique, Ingénierie pour le Vivant (IRIV)
    • Masters Chimie
    • Ecole Universitaire de Recherche QMat
  • Equipex/Labex
    • UNION
    • UTEM
    • NIE
    • Inauguration des EquipEx
  • Partenariats
    • CARMEN – Laboratoire commun
    • Institut Carnot MICA
    • Start’Up SuperBranche
    • Fédération Matériaux et Nanosciences Alsace
    • Fondation pour la Recherche en Chimie
    • A l’International
      • LIA LaFICS
      • Collège doctoral franco-allemand
      • Rhin Solar
  • Plateformes
    • Nanofabrication
    • Microscopie Electronique
    • Plateforme de diffraction des rayons X
    • Caractérisation Optique
    • Calcul Scientifique
Navigation
Fsec X-ray crystallography of retinal proteins

Fsec X-ray crystallography of retinal proteins

Since more than 20 years, there has been a tremendous effort both on packing proteins in crystals and on improving synchrotrons so as to make high performance protein crystallography a routine task. This has allowed to resolve the structure of thousands of proteins, regardless of them being soluble or embedded in membranes. Since a few years, a new revolution is on the way with the advent of X-ray free electron lasers (FELs), capable of producing the most intense and shortest X-ray pulses on earth. Facilities such as the Linac Coherent Light Source (LCLS, Stanford) or the European FEL (XFEL in Hamburg) offer users the possibility to conduct time-resolved X-ray experiments with variable energies (diffraction, scattering, XANES), in a laser-pump/X-ray-probe operation, with down to ≈30 fs time resolution.

Such pump-probe experiments have been applied in recent years to photo-sensitive proteins, allowing to observe photo-initiated motion of the protein-forming molecules, the light-absorbing chromophore and amino acids, with atomic resolution (1.5 Å). Rhodopsin, the photo-sensor of vision, has not been subjected to an FEL yet, but its cousin, bacterio-rhodopsin (bR) was. The latter is used by archaebacteria in a primitive form of photo-synthesis to generate ATP. bR thus stands as an example of the large family of retinal proteins, used for diverse functions by microbacteria. It is known that the chromophore retinal undergoes a trans-cis isomerisation upon absorption of light, and standard lab-based laser spectroscopy has shown in the late 1980’s[1] that this is accomplished in half a picosecond or less (5x 10-13 s) !

In the past months, two femtosecond X-ray diffraction experiments reported astounding details of the photo-initiated motion of retinal, and of the amino acids and water molecules forming the retinal binding pocket: within less than 200 fs, when retinal is in an excited state, it slightly stretches and twists, hydrogen-bonds are disrupted, and one water molecule “disappears” [1,2]. The theoretically predicted aborted bicycle-pedal mechanism for isomerisation, a special form of synchronised rotation about two C-C bond axes of the retinal backbone, was confirmed. In the second paper [2], an international consortium led by I. Schlichting (Max-Planck-Institute Heidelberg), including S. Haacke at IPCMS, reports coherent oscillations both of the retinal as well as of some key amino acids, flanking retinal. The paper highlights the electronic and vibrational coupling of retinal and its environment, which will be crucial to account for fully in the next generation of extended quantum chemistry simulations, and which is probably key to understand the catalytic effect the protein exerts on the photo-isomerisation reaction.

picture comment Haacke

However, the paper by Nass Kovacs et al., conveys a second important message, which is likely to trigger profound changes in the way the community will be performing these laser-pump/X-ray-probe in the future. Indeed, most of the published papers ignored the excessively high laser intensities leading to multi-photon effects in the high density crystals, and even to permanent photo-bleaching or melting of the crystals. Nass Kovacs et al. identified these multi-photon excitation pathways and characterised the most prominent one due to sequential two-photon absorption. It was shown that “more is less”, i.e. higher laser powers bring the protein into non-reactive highly excited states, instead of optimizing the concentration of photo-isomerising proteins. The future challenge is now to fully exploit the synergy of lab-based laser spectroscopy and X-ray crystallography so as to work under reduced laser intensities, ideally mimicking the excitation by sunlight.

 

[1] Charles Shank, one of the pioneers, will be at IPCMS on Monday 16th September. Don’t miss his talk.

References :
[1] P. Nogly et al., Science 361, eaat0094 (2018)
[2] G. Nass Kovacs et al., Nature Comm., 10, 3711 (2019)

Institut de Physique et de Chimie des Matériaux de Strasbourg

  • /Crédits
  • /Mentions légales
  • /Se connecter
Optimization WordPress Plugins & Solutions by W3 EDGE