Abstract
We report new experimental results on the ultrafast photo-isomerization of ASR - PSBR where, unlike other retinal proteins, point mutations lead to a 2-fold increase of the photo-isomerization speed for the all-trans isomer. Prominent low-frequency vibrational coherences are reported for both the excited and photo-product ground states.
Highlights
Anabaena sensory rhodopsin (ASR) is a microbial retinal protein for which the protonated Schiff base of retinal (PSBR) adopts two different conformations in the ground state, the all-trans,15-anti (AT) and 13-cis, 15-syn (13C)
We report on point-mutated proteins showing an up to ~2 fold reduction of the AT isomer excited state lifetime (ESL) with respect to WT-ASR, with a trend indicating a correlation between ESL and absorption maximum wavelength [4]
Transient absorption (TA) experiments were performed with a 1-kHz Ti:Sa amplifier, pumping a home-built NOPA that provides 40fs Fourier-limited excitation pulses in the range of 520-560nm
Summary
Anabaena sensory rhodopsin (ASR) is a microbial retinal protein for which the protonated Schiff base of retinal (PSBR) adopts two different conformations in the ground state, the all-trans,15-anti (AT) and 13-cis, 15-syn (13C). Related to the biological function of ASR being a light-intensity sensor, the isomer ratio depends upon illumination conditions (intensity and wavelength) reaching a photostationary, socalled light adapted (LA) state. The interest of studying the primary steps of retinal proteins’ photo-cycle via femtosecond spectroscopy originates from a long-standing question, on how the protein environment tunes and optimizes the photoisomerization reaction speed and yield.
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