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Profil 98/99 Femtosecond dynamics of electronic excitations and nuclear motion in the native bacteriorhodopsin and its mutants

Applicant Haacke Stefan
Number 55830
Funding scheme PROFIL
Research institution Institut des sciences et ingénierie chimiques EPFL - SB - ISIC
Institution of higher education University of Lausanne - LA
Main discipline Other disciplines of Engineering Sciences
Start/End 01.07.1999 - 31.08.2004
Approved amount 684'875.00
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Keywords (5)

Retinal proteins; femtosecond spectroscopy; structural dynamics; dielectric relaxation; membrane proteins

Lay Summary (English)

Lay summary
The present proposal addresses the ultrafast dynamics of protonatedretinal Schiff bases (PSBR) in solvents and different protein environmentsusing innovative fluorescence up-conversion and femtosecond pump&probeexperiments. Particular emphasis is put on identifying intra-molecularprocesses (vibrational relaxation and photo-isomerization) andinter-molecular interactions with the dielectric environment (dipolarsolvation and thermalization) related with the photo-isomerization ofretinal. The aim of this research is to understand on a molecular levelthe “catalytic” role of the protein environment for the isomerizationprocess. It has indeed been recognized long ago that the speed and bondselectivity of this process depend critically on the environment. Besidesthe steric constraints inherent to the protein, the electrostaticproperties of the latter determine the isomerization. In addition, theprotein is being polarized and thus changes the internal electric fielddistribution as a response to the optical excitation of the chromophore.However, the molecular mechanisms of these static and dynamic aspects arenot understood yet, which is precisely the purpose of this researchproposal.
The latest results yielded important new information: In a recent study ofthe time- and wavelength-resolved fluorescence of PSBR in differentsolvents, we have characterized the spectral and temporal kinetics ofintra- and intermolecular processes. We are now in a good position torecognize how the latter are modified in different protein environments(bacteriorhodopsin and mutants thereof, sensory rhodopsin II, etc.). Inaddition, our novel VIS-pump/UV-probe experiment is able to detectultrafast changes in the tryptophan absorption band. As the tryptophansare sensitive local probes, we have been able to monitor for the firsttime the time-dependent excited state dipole moment of retinal. We alsoobtained indications for a transient photo-induced polarization of theprotein matrix. Details of the observed dynamics are analyzed incollaboration with theoreticians (Prof. M. Olivucci, U Siena; Prof. G.v.d. Zwan, U Amsterdam). In brief, we have the experimental andtheoretical tools to obtain further insights into the molecular mechanismsunderlying the protein-specific photo-isomerization reaction.
In a more general context, electrostatic and structural properties ofproteins are optimized to fulfill the primary processes (charge transfer,radical formation, or photoisomerization) initiating the biologicalfunction. bR is a good model system with general importance forphotosensor proteins in general. A detailed knowledge of how the proteincontrols photo-isomerization may be generally useful for photosensoryproteins and for the design of bio-mimetic molecular switches andmotors.
Direct link to Lay Summary Last update: 21.02.2013

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