First steps of retinal photoisomerization in proteorhodopsin.
The early steps (<1 ns) in the photocycle of the detergent solubilized proton pump proteorhodopsin are analyzed by ultrafast spectroscopic techniques. A comparison to the first primary events in reconstituted proteorhodopsin as well as to the well known archaeal proton pump bacteriorhodopsin is given. A dynamic Stokes shift observed in fs-time-resolved fluorescence experiments allows a direct observation of early motions on the excited state potential energy surface. The initial dynamics is dominated by sequentially emerging stretching (<150 fs) and torsional (approximately 300 fs) modes of the retinal. The different protonation states of the primary proton acceptor Asp-97 drastically affect the reaction rate and the overall quantum efficiencies of the isomerization reactions, mainly evidenced for time scales above 1 ps. However, no major influence on the fast time scales (approximately 150 fs) could be seen, indicating that the movement out of the Franck-Condon region is fairly robust to electrostatic changes in the retinal binding pocket. Based on fs-time-resolved absorption and fluorescence spectra, ground and exited state contributions can be disentangled and allow to construct a reaction model that consistently explains pH-dependent effects in solubilized and reconstituted proteorhodopsin.
Lenz
Martin O
MO
Institut für Physikalische und Theoretische Chemie, Johann-Wolfgang-Goethe-Universität, Frankfurt, Germany.
Huber
Robert
R
Schmidt
Bernhard
B
Gilch
Peter
P
Kalmbach
Rolf
R
Engelhard
Martin
M
Wachtveitl
Josef
J
D007536:Isomerism; D008027:Light; D010777:Photochemistry / Q000379:methods; D012172:Retinaldehyde / Q000737:chemistry* / Q000528:radiation effects*; D012243:Rhodopsin / Q000737:chemistry* / Q000528:radiation effects*; D025604:Rhodopsins, Microbial
D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D012243:Rhodopsin; D012172:Retinaldehyde