Isomerization Dynamics of Wild Type and Mutated Anabaena Sensory Rhodopsin Mapped by Time-Resolved Coherent Raman Spectroscopy

Abstract

The light 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 [1]. The ground state structure of the RPSB and its surrounding protein architecture are known to play a central role in this reaction. It has been a longstanding question how each factor individually influences the reaction dynamics. In this context, Anabaena Sensory Rhodopsin (ASR), a recently discovered microbial retinal protein, serves as an ideal system to answer this question as it binds two structural isomers (all-trans and 13-cis) of the RPSB within the same protein constructions in its photocycle. In this work, the photo-isomerization dynamics of the RPSB in ASR has been explored with the help of time resolved coherent Raman techniques like pump-degenerate four-wave-mixing (pump-DFWM) (Fig. 1(a)) and pump-impulsive vibrational spectroscopy (pump-IVS). Both methods report on the structural changes of the RPSB during the photochemical reaction by tracking the transient frequency shifts of the vibrational modes in the excited state.