TY  - GEN
Y1  - 2019///
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/26114/
ID  - heidok26114
AV  - public
TI  - Femtosecond Coherent Vibrational Dynamics of Anabaena Sensory Rhodopsin
A1  - Roy, Partha Pratim
N2  - The photo-induced isomerization of retinal protonated Schiff base (RPSB) inside the protein
pocket is one of the fastest (<ps) and most stereo-selective photochemical reactions in nature. The
ground state structure of the RPSB and its surrounding protein constructions are thought to be the
two most crucial factors to drive this reaction. The investigation of each factor individually was
the main goal of this thesis. Anabaena Sensory Rhodopsin (ASR), a recently discovered microbial
retinal protein, serves as an ideal system for this study as it binds two structural isomers (all-trans:
AT and 13-cis: 13C) of the RPSB within the same protein constructions in its photocycle. In the
present work, the photo-induced dynamics of the RPSB in ASR has been explored with the help
of time resolved coherent vibrational spectroscopic methods, which monitor the photo-induced
sub-ps structural changes of the RPSB. These studies have helped to shed light on the intricate
relationship between electronic and vibrational dynamics of the RPSB.
In the first half of this thesis, a comparative study showed both electronic and vibrational dynamics
are widely distinct for the AT and 13C isomers of the RPSB in ASR. In particular, the 13C isomer
exhibited more than five folds faster dynamics than the AT isomer. One possible molecular origin
behind this dynamical difference was found by comparing the ground state Raman spectra of the
two isomers. It depicted an increase in the amplitude of hydrogen-out-of-plane (HOOP) modes for
the 13C isomer, which is usually considered to be an evidence of distortion in the ground state
structure for the retinal system. The ground state pre-distortion has been reported as a potential
element for the acceleration of the isomerization reaction for the 13C isomer, in analogy with the
cis isomers of visual rhodopsin and bacteriorhodopsin.
The second half of this work explored the role of the part of protein helix inside the retinal pocket
as well as that far away from the pocket. In particular, the replacement of the amino acid residues
in vicinity of the RPSB by point mutation caused an acceleration of the reaction rate for the AT
isomer, but it had only a minor effect for the 13C isomer of the RPSB. Furthermore, the truncation
of the part of the protein, embedded into the cytoplasmic region, affected the formation of the
primary photoproduct. All these experimental results lead to two major conclusions of this thesis:
(i) the protein constructions govern the retinal isomerization dynamics and (ii) the same protein
cage exerts differential interactions on two structural isomers of the RPSB.
ER  -