Abstract
The effects of the initial retinal configuration and the active isomerization coordinate on the photochemistry of retinal proteins (RPs) are assessed by comparing photochemical dynamics of two stable retinal ground state configurations (all-trans ,15-anti vs. 13-cis ,15-syn ), within two RPs: Bacteriorhodopsin (BR) and Anabaena Sensory Rhodopsin (ASR). Hyperspectral pump-probe spectroscopy shows that photochemistry starting from 13-cis retinal in both proteins is 3-10 times faster than when started in the all-trans state, suggesting that the hastening is ubiquitous to microbial RPs, regardless of their different biological functions and origin. This may also relate to the known disparity of photochemical rates between microbial RPs and visual pigments. Importance and possible underlying mechanisms are discussed as well.
Highlights
Introduction and MotivationPhotochemistry in retinal proteins is determined both by properties of the retinal chromophore and by its interactions with the surrounding protein [1]
This is achievable in Bacteriorhodopsin (BR) and Anabaena Sensory Rhodopsin (ASR), two microbial retinal proteins (MRPs) which exist in two stable ground state forms of their retinal protonated Schiff base chromophore: alltrans,15-anti (XAT) and 13-cis,15-syn (X13C)
BR, the well known proton pump, and the newly-identified photoswitchable ASR [7] perform very different biological functions. Both exhibit much faster timescales of internal conversion (IC) when initiated in the 13-cis rather than all-trans ground state of the retinal, suggesting that the disparity in rates may be ubiquitous to all MRPs
Summary
Photochemistry in retinal proteins is determined both by properties of the retinal chromophore and by its interactions with the surrounding protein [1]. The importance of the initial retinal configuration can be best assessed in isolation by comparing photoisomerization dynamics of different retinal ground state configurations within the same protein. This is achievable in Bacteriorhodopsin (BR) and Anabaena Sensory Rhodopsin (ASR), two MRPs which exist in two stable ground state forms of their retinal protonated Schiff base chromophore: alltrans,15-anti (XAT) and 13-cis,15-syn (X13C). Experiments reported here compare IC dynamics starting from either ground state by conducting hyperspectral pump-probe spectroscopy with sub100 fs temporal resolution on dark-adapted and light-adapted samples of both proteins [see 3,4]
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