%0 Generic
%A Roy, Partha Pratim
%D 2019
%F heidok:26114
%R 10.11588/heidok.00026114
%T Femtosecond Coherent Vibrational Dynamics of Anabaena Sensory Rhodopsin
%U https://archiv.ub.uni-heidelberg.de/volltextserver/26114/
%X 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.