|Ultrafast spectroscopy of tryptophan as molecular probe for protein dynamics in the condensed phase||Séminaires SPAM LFP
|08/10/2009 à 11h00
LIDYL Bât 522, p 138 CEA-Saclay
|Prof. Stefan HAACKE
|Light is used by bacteria as energy source (photo-synthesis) or for orientation (photo-taxis). On the molecular level, proteins are driving the underlying often complex bio-chemical machinery, and an ultrafast photochemical process is the starting point of these processes. In photo-sensory proteins, like the visual photo-receptor rhodopsin, this involves photo-isomerisation, but more and more examples are known where photo-induced charge transfer is the energy-converting process. The present talk will review the recent progress made in understanding the ultrafast photo-physics of bacteriorhodopsin, the key element of archaebacterial photo-synthesis. Our focus is on the lightinduced dipole moment change, and how this can be measured via the response of tryptophan amino acids [1,2].
When the photo-physics of rhodopsin's retinal is mimicked in artificial, computer-designed molecules, interesting new model systems are obtained, the so-called indanone-pyrollene photo-switches. We will show that their photo-reaction occurs coherently, i.e. in concert among the ensemble of molecules, within half a torsional period . On the way of exploring new ways for using tryptophans as molecular probes in protein/DNA complexes, we have been revisiting tryptophan's excited state quenching in aqueous solution. Quenching leads to a primary photo-product, with a well-defined absorption band at 425 nm. In contrast to previous nanosecond photolysis experiments, it has now been possible to follow the subnanosecond formation dynamics of this photo-product, shedding new light on its molecular nature .
 “Probing the Ultrafast Charge Translocation of Photoexcited Retinal in Bacteriorhodopsin”, S. Schenkl, F.van
Mourik, G. van der Zwan, S. Haacke, M. Chergui, Science 309, 917-921 (2005).
“Functional electric field changes in photo-activated proteins revealed by ultrafast Stark spectroscopy of
the Trp residues”, J. Léonard, et al., Proc. Nat. Acad. Sci. USA, in press (2009).
 “An artificial molecular switch that mimics the visual pigment and completes its photocycle in picoseconds”,
A. Sinicropi, et al., Proc. Nat. Acad. Sci. USA, 105,17642-17647 (2008).
"On the Nature and Formation Dynamics of Tryptophan's Primary Photoproduct in Water Solution", D.
Sharma, J. Léonard, S. Haacke, submitted.